Case Study: Hormonal Havoc<\/h1>\r\n<\/div>\r\nEighteen-year-old Gabrielle checks her calendar. It has been 42 days since her last menstrual period, which is two weeks longer\u00a0than the length of the average woman\u2019s menstrual cycle. Although many women would suspect pregnancy if their period was late, Gabrielle has not been sexually active. She is not even sure she is \u201clate,\u201d because her period has never been regular. Ever since her first period\u00a0when she was 13 years old, her cycle lengths have varied greatly, and there are months where she does not get a period at all. Her mother told her that a girl\u2019s period is often irregular when it first starts, but five years later, Gabrielle\u2019s still has not become regular. She decides to go to the student health center on her college campus to get it checked out.\r\n\r\nThe doctor asks her about the timing of her menstrual periods and performs a pelvic exam. She also notices that Gabrielle is overweight, has acne, and excess facial hair. As she explains to Gabrielle, while these physical characteristics can be perfectly normal, in combination with an irregular period, they can be signs of a disorder of the endocrine \u2014 or hormonal \u2014 system called polycystic ovary syndrome<\/a> (PCOS).\r\n\r\nIn order to check for PCOS, the doctor refers Gabrielle for a pelvic ultrasound and sends her to the lab to get blood work done. When her lab results come back, Gabrielle learns that her levels of androgens (a group of hormones) are high, and so is her blood glucose (sugar). The ultrasound showed that she has multiple fluid-filled sacs (known as cysts) in her ovaries. Based on Gabrielle\u2019s symptoms and test results, the doctor tells her that she does indeed have PCOS.\r\n\r\nPCOS is common in young women. It is estimated that 6-10% women of childbearing age have PCOS \u2014 as many as 1.4 million women in in Canada. You may know someone with PCOS, or you may have it yourself.\r\n\r\nRead the rest of this chapter to learn about the glands and hormones of the endocrine system, their functions, how they are regulated, and the disorders \u00ad\u00ad\u2014 such as PCOS \u00ad\u00ad\u2014 that can arise when hormones are not regulated properly. At the end of the chapter, you will learn more about PCOS, its possible long-term consequences (including fertility problems and diabetes), and how these negative outcomes can sometimes be prevented with lifestyle changes and medications.\r\n\r\n\r\nChapter Overview: Endocrine System<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nIn this chapter, you will learn about the endocrine system, a system of glands that secrete hormones that regulate many of the body\u2019s functions. Specifically, you will learn about:\r\n\r\n \t- The [pb_glossary id=\"2936\"]glands[\/pb_glossary] that make up the [pb_glossary id=\"5985\"]endocrine system[\/pb_glossary], and how [pb_glossary id=\"5661\"]hormone[\/pb_glossary]s act as chemical messengers in the body.<\/li>\r\n \t
- The general types of endocrine system disorders.<\/li>\r\n \t
- The types of endocrine hormones \u2014 including steroid hormones (such as sex hormones) and non-steroid hormones (such as insulin) \u2014 and how they affect the functions of their target cells by binding to different types of receptor proteins.<\/li>\r\n \t
- How the levels of hormones are regulated mostly through negative, but sometimes through positive, feedback loops.<\/li>\r\n \t
- The master gland of the endocrine system, the [pb_glossary id=\"2938\"]pituitary gland[\/pb_glossary], which controls other parts of the endocrine system through the hormones that it secretes, as well as how the pituitary itself is regulated by hormones secreted from the [pb_glossary id=\"2937\"]hypothalamus[\/pb_glossary] of the brain.<\/li>\r\n \t
- The [pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary] and its hormones \u2014 which regulate processes including metabolism and calcium [pb_glossary id=\"5761\"]homeostasis[\/pb_glossary] \u2014 how the thyroid is regulated, and the disorders that can occur when there are problems in thyroid hormone regulation (such as hyperthyroidism and hypothyroidism).<\/li>\r\n \t
- The [pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary], which secrete hormones that regulate processes such as metabolism, electrolyte balance, responses to stress, and reproductive functions, and the disorders that can occur when there are problems in adrenal hormone regulation, such as Cushing\u2019s syndrome and Addison\u2019s disease.<\/li>\r\n \t
- The [pb_glossary id=\"3197\"]pancreas[\/pb_glossary], which secretes hormones that regulate blood glucose levels (such as insulin), and disorders of the pancreas and its hormones, including [pb_glossary id=\"2969\"]diabetes[\/pb_glossary].<\/li>\r\n<\/ul>\r\nLater chapters in this book will discuss the glands and hormones involved in the reproductive and immune systems in more depth.\r\n\r\n<\/div>\r\n<\/div>\r\n\r\n\r\nAs you read this chapter, think about the following questions:\r\n
\r\n \t- Why can hormones have such broad range effects on the body, as we see in PCOS?<\/li>\r\n \t
- Which hormones normally regulate blood glucose? How is this related to diabetes?<\/li>\r\n \t
- What are androgens? How do you think their functions relate to some of the symptoms that Gabrielle is experiencing?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
Attribution<\/h2>\r\nFigure 9.1.1<\/strong>\r\n\r\nChapter 9 case study<\/a> [photo] by niklas_hamann<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReference<\/h2>\r\n
Mayo Clinic Staff. (n.d.). Polycystic ovary syndrome [online article]. MayoClinic.com. https:\/\/www.mayoclinic.org\/diseases-conditions\/pcos\/multimedia\/polycystic-ovary-syndrome\/img-20007768<\/p>","rendered":"
<\/p>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Chapter-9-case-studey-by-niklas_hamann-Pe4gh8a8mBY-unsplash-scaled-3.jpg\")
Figure 9.1.1 Could this woman have PCOS?<\/em><\/figcaption><\/figure>\n\nCase Study: Hormonal Havoc<\/h1>\n<\/div>\n
Eighteen-year-old Gabrielle checks her calendar. It has been 42 days since her last menstrual period, which is two weeks longer\u00a0than the length of the average woman\u2019s menstrual cycle. Although many women would suspect pregnancy if their period was late, Gabrielle has not been sexually active. She is not even sure she is \u201clate,\u201d because her period has never been regular. Ever since her first period\u00a0when she was 13 years old, her cycle lengths have varied greatly, and there are months where she does not get a period at all. Her mother told her that a girl\u2019s period is often irregular when it first starts, but five years later, Gabrielle\u2019s still has not become regular. She decides to go to the student health center on her college campus to get it checked out.<\/p>\n
The doctor asks her about the timing of her menstrual periods and performs a pelvic exam. She also notices that Gabrielle is overweight, has acne, and excess facial hair. As she explains to Gabrielle, while these physical characteristics can be perfectly normal, in combination with an irregular period, they can be signs of a disorder of the endocrine \u2014 or hormonal \u2014 system called polycystic ovary syndrome<\/a> (PCOS).<\/p>\nIn order to check for PCOS, the doctor refers Gabrielle for a pelvic ultrasound and sends her to the lab to get blood work done. When her lab results come back, Gabrielle learns that her levels of androgens (a group of hormones) are high, and so is her blood glucose (sugar). The ultrasound showed that she has multiple fluid-filled sacs (known as cysts) in her ovaries. Based on Gabrielle\u2019s symptoms and test results, the doctor tells her that she does indeed have PCOS.<\/p>\n
PCOS is common in young women. It is estimated that 6-10% women of childbearing age have PCOS \u2014 as many as 1.4 million women in in Canada. You may know someone with PCOS, or you may have it yourself.<\/p>\n
Read the rest of this chapter to learn about the glands and hormones of the endocrine system, their functions, how they are regulated, and the disorders \u00ad\u00ad\u2014 such as PCOS \u00ad\u00ad\u2014 that can arise when hormones are not regulated properly. At the end of the chapter, you will learn more about PCOS, its possible long-term consequences (including fertility problems and diabetes), and how these negative outcomes can sometimes be prevented with lifestyle changes and medications.<\/p>\n
\n\n\nChapter Overview: Endocrine System<\/span><\/h1>\n<\/header>\n\nIn this chapter, you will learn about the endocrine system, a system of glands that secrete hormones that regulate many of the body\u2019s functions. Specifically, you will learn about:<\/p>\n
\n- The glands<\/a> that make up the endocrine system<\/a>, and how hormone<\/a>s act as chemical messengers in the body.<\/li>\n
- The general types of endocrine system disorders.<\/li>\n
- The types of endocrine hormones \u2014 including steroid hormones (such as sex hormones) and non-steroid hormones (such as insulin) \u2014 and how they affect the functions of their target cells by binding to different types of receptor proteins.<\/li>\n
- How the levels of hormones are regulated mostly through negative, but sometimes through positive, feedback loops.<\/li>\n
- The master gland of the endocrine system, the pituitary gland<\/a>, which controls other parts of the endocrine system through the hormones that it secretes, as well as how the pituitary itself is regulated by hormones secreted from the hypothalamus<\/a> of the brain.<\/li>\n
- The thyroid gland<\/a> and its hormones \u2014 which regulate processes including metabolism and calcium homeostasis<\/a> \u2014 how the thyroid is regulated, and the disorders that can occur when there are problems in thyroid hormone regulation (such as hyperthyroidism and hypothyroidism).<\/li>\n
- The adrenal glands<\/a>, which secrete hormones that regulate processes such as metabolism, electrolyte balance, responses to stress, and reproductive functions, and the disorders that can occur when there are problems in adrenal hormone regulation, such as Cushing\u2019s syndrome and Addison\u2019s disease.<\/li>\n
- The pancreas<\/a>, which secretes hormones that regulate blood glucose levels (such as insulin), and disorders of the pancreas and its hormones, including diabetes<\/a>.<\/li>\n<\/ul>\n
Later chapters in this book will discuss the glands and hormones involved in the reproductive and immune systems in more depth.<\/p>\n<\/div>\n<\/div>\n
\nAs you read this chapter, think about the following questions:<\/p>\n
\n- Why can hormones have such broad range effects on the body, as we see in PCOS?<\/li>\n
- Which hormones normally regulate blood glucose? How is this related to diabetes?<\/li>\n
- What are androgens? How do you think their functions relate to some of the symptoms that Gabrielle is experiencing?<\/li>\n<\/ol>\n<\/div>\n<\/div>\n
Attribution<\/h2>\n
Figure 9.1.1<\/strong><\/p>\nChapter 9 case study<\/a> [photo] by niklas_hamann<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\nReference<\/h2>\n
Mayo Clinic Staff. (n.d.). Polycystic ovary syndrome [online article]. MayoClinic.com. https:\/\/www.mayoclinic.org\/diseases-conditions\/pcos\/multimedia\/polycystic-ovary-syndrome\/img-20007768<\/p>\n
definition<\/span>Created by: CK-12\/Adapted by Christine Miller<\/p>\n
\n<\/div>\n<\/div>\nFigure 6.3.1 How would you classify these people?\u00a0<\/em><\/p>\nWhy Classify?<\/h1>\n
What do you see when you look at Figure 6.3.1? Did you sort individuals into categories based in gender, age, body type, facial features, skin colour or other characteristics?\u00a0 As humans, we seem to have a penchant for classifying and labeling people and things. It helps us establish a sense of order in the world around us. The 18th century taxonomist Carl Linnaeus<\/a>, for example, classified virtually all known living things into different species, genera, families, and other taxonomic categories. His classifications were based on observable phenotypic characteristics, such as skin colour. Modern biological classifications of living things are usually based on phylogenetic relationships. Phylogenies reflect evolutionary history and group together living things that are related by descent from a common ancestor.<\/p>\nStarting with Linnaeus and continuing to the present, scientists and others have attempted to classify human variation. There are three basic approaches to classification: typological, populational, and clinal.<\/p>\n
\nTypological Approach<\/h2>\n<\/div>\n
The\u00a0typological approach\u00a0involves creating a\u00a0typology<\/a>,<\/strong>\u00a0which is a system of discrete types, or categories. This approach was widely used by scientists up through the early 20th century. Racial classifications are typological classifications. They place people into a small number of discrete categories, or\u00a0races,<\/strong> based on a few readily observable traits, such as skin colour, hair texture, facial features, and body build.<\/p>\nRacial Classifications and Racism<\/h2>\n
Racial classifications of humans probably go back as long as people distinguished \u201cus\u201d from \u201cthem.\u201d An early \u201cscientific\u201d classification of humans into races is Linnaeus\u2019 1735 classification. He divided\u00a0Homo sapiens<\/em>\u00a0into continental races, which he named\u00a0europaeus, asiaticus, americanus,<\/em>\u00a0and\u00a0afer.<\/em> Linnaeus described these races in terms of observable physical traits. He also associated, inaccurately, each race with different personality qualities and behaviors. For example, he described Homo sapiens europaeus<\/em>\u00a0as active and adventurous and\u00a0Homo sapiens afer<\/em>\u00a0as lazy and careless. In 1795, the German naturalist Johann Friedrich Blumenbach<\/a> proposed five major races of\u00a0Homo sapiens<\/em>, which he named the caucasoid, mongoloid, negroid, American Indian, and Malayan races. Blumenbach thought that the caucasoid race was the original race, and that the other races arose in a process of \u201cdegeneration\u201d from the caucasoids.<\/p>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Huxley_races.png\")
Figure 6.3.2 Huxley proposed that humans were categorized into nine races, and distributed geographically as shown in this map. Each colour represents one of Huxley\u2019s proposed races. These categories included \u201cAustraloid,\u201d \u201cXanthochroi,\u201d \u201cMelanochori,\u201d \u201cNegroes,\u201d and \u201cMongoloids,\u201d and they are not used today.<\/em><\/figcaption><\/figure>\nIn 1870, the English biologist Thomas Huxley<\/a> classified\u00a0Homo sapiens<\/em> into nine races which were distributed geographically<\/span>. The map in Figure 6.3.2 shows how Huxley thought the races were distributed worldwide. Each colour represents one of Huxley\u2019s proposed races. These categories included \u201cAustraloid,\u201d \u201cXanthochroi,\u201d \u201cMelanochori,\u201d \u201cNegroes,\u201d and \u201cMongoloids,\u201d and they are not used today. <\/span>It should be noted that Huxley did not hold such strong negative stereotypes about non-European (or non-caucasoid) races as did his intellectual forebears. Huxley, however, still attributed different behaviors to racial groups that had nothing to do with the colour of their skin or continent of origin.<\/p>\nBy the early 20th century, so-called\u00a0scientific racism<\/a><\/strong> was a popular ideology. This was the idea that race is a biological concept and that human behavior is partly determined by race. At around 1950, in a series of groundbreaking studies of skeletal anatomy, anthropologist Franz Boas<\/a> showed that cranial (skull) shape and size were highly malleable, depending on environmental factors (such as health and nutrition). He contrasted this with\u00a0racial anthropologists'\u00a0claims that head shape is a stable racial trait. In this way, Boas demonstrated that this commonly used racial trait was determined by the environment, and not just genes. Boas also worked to demonstrate that differences in human behavior are not determined primarily by innate biological dispositions, but are largely the result of cultural differences acquired through social learning.<\/p>\nUnfortunately,\u00a0racism<\/a><\/strong> still persists today \u2014 in society at large, if not in science. This is the association of racial traits (such as skin colour) with unrelated traits (such as intelligence), often leading to prejudice and discrimination against people based only on how they look. The concept of human race is real, not in a biological sense, but in a social sense. Racial stereotypes and racism are deeply ingrained in our history and culture, and they have real material effects on human lives.<\/p>\nAdditional Problems with Typological Classification<\/h2>\n
Besides the problem of racism, there are other problems with typological approaches to the biological classification of\u00a0Homo sapiens.<\/em>\u00a0One problem is that most human biological traits are not either present or absent, but instead vary on a continuum. This type of distribution cannot be adequately represented by discrete categories, such as races. The typological approach also results in groupings of people that may be similar in terms of some traits, but not others. How people are grouped together depends on which traits are chosen. In addition, the number of groups that are needed to classify people depends on the number of traits that are used. The greater the number of traits, the greater the number of racial categories there must be. If racial categories depend on the traits chosen to define them, it is clear that the racial classifications are arbitrary and do not reflect biological reality.<\/p>\nAnother problem with typological classifications is that they lead to the mistaken belief that people within typological categories are more similar to each other than they are to people in other categories. There is actually more variation\u00a0within<\/em>\u00a0than\u00a0between<\/em> typological groups. An estimated 90 per cent of human genetic variation occurs between people within races, and only 10 per cent occurs between races. Clearly, races are far from homogenous in terms of their genetic composition. In short, we are all more alike than we are different.<\/p>\n\nPopulational Approach<\/h1>\n<\/div>\n
By the middle of the 20th century, scientists started advocating a\u00a0populational approach<\/strong>\u00a0to classifying\u00a0Homo sapiens.<\/em>\u00a0This approach is based on the idea that the breeding population is the only biologically meaningful group. The\u00a0breeding population<\/a><\/strong>\u00a0is the unit of evolution, and it includes people who have mated and produced offspring together for many generations. As a result, members of the same breeding population should share many genetic traits. You would also expect them to have many of the same phenotypic traits, because of their similar genetic makeup.<\/p>\nWhile the populational approach makes sense in theory, in reality, it can rarely be applied, because most human populations are not closed breeding populations. Some people have always selected mates from outside their local population (even mating with archaic humans such as Neanderthals). This tendency has increased dramatically in recent centuries with the advent of efficient means of traveling long distances. As a consequence, there are very few remaining distinct breeding populations within the human species.<\/p>\n![\"Nicobar_Islands\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Nicobar_Islands.png\")
Figure 6.3.3 The Andaman Islands are boxed in red on this map of South and Southeast Asia.<\/em><\/figcaption><\/figure>\nAn example of one such population is the Sentinelese<\/a>, a small population of hunter-gatherers who live alone on a small island in the Andaman Islands (see the map). The Sentinelese are thought to be direct descendants of the first modern humans to leave Africa, and they may have lived in the Andaman Islands for as long as 60 thousand years. The Sentinelese are also one of the most isolated human populations on Earth. The fact that their language is distinctly different from other Andaman Islands languages is evidence that they have had little contact with other people for thousands of years. Although closed breeding populations (such as the Sentinelese) may be useful for investigating questions about evolutionary processes, they are not useful for classifying most of humanity.<\/p>\n <\/p>\n
\nClinal Approach<\/span><\/p>\n<\/div>\nBy the 1960s, scientists began to use a\u00a0clinal approach<\/strong>\u00a0to classify human variation. This approach maps variation in traits over geographic regions (such as continents) or even worldwide. Clinal models are a useful way of describing human variation that does not lead to discrete races or other categories of people.<\/p>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Map_of_Group_O.png\")
Figure 6.3.4 Distribution of Type O Blood in Indigenous Populations of the World.<\/em><\/figcaption><\/figure>\nIn Figure 6.3.4 you can see a worldwide clinal map for type O blood in the human ABO blood group system. The frequency of this trait is shown for the indigenous populations of various regions. It is lowest throughout Asia and highest in Native American populations in both North and South America. This geographic distribution results from the complex interaction of a variety of factors, including natural selection, genetic drift, and gene flow. You can read more about geographic variation in blood types in the concept Variation in Blood Types.<\/em><\/p>\n\nClinal maps for many genetic traits show variation that changes gradually from one geographic area to another, which may happen because of the nature of gene flow. Gene flow occurs when mating takes place between people in different populations. The likelihood of mating with others depends on their distance from us. You may not marry the boy or girl next door, but your mate is more likely to be someone in the same state or country than someone on another continent.<\/span><\/p>\n<\/div>\nNatural selection has a major impact on the clinal distribution of some traits, because variation in the traits tracks variation in selective pressures. For example, the environmental stressor of malaria varies throughout Africa with climate, as you can see in the left-hand map below (Figure 6.3.5). The sickle cell trait that protects from malaria has a similar distribution, as shown in the right-hand map.<\/p>\n
\n<\/div>\n<\/div>\nFigure 6.3.5\u00a0<\/em><\/p>\n\n\n6.3 Summary<\/span><\/h1>\n<\/header>\n\n\n- Humans seem to have a need to classify<\/a> and label people based on their similarities and differences. Three approaches to classifying human variation include typological, populational, and clinal approaches.<\/li>\n
- The typological approach involves creating a typology, which is a system of discrete categories, or races. This approach was widely used by scientists until the early 20th century. Racial categories are based on observable phenotypic traits (such as skin colour), but other traits and behaviors are often assumed to apply to racial groups, as well. The use of racial classifications often leads to racism<\/a>.<\/li>\n
- By the mid-20th century, scientists started advocating a population approach. This assumes that the breeding population, which is the unit of evolution, is the only biologically meaningful group. While this approach makes sense in theory, in reality, it can rarely be applied to actual human populations. With few exceptions, most human populations are not closed breeding populations.<\/li>\n
- By the 1960s, scientists began to use a clinal approach to classify human variation. This approach maps variation in the frequency of traits or alleles over geographic regions or worldwide. Clinal maps for many genetic traits show variation that changes gradually from one geographic area to another. This type of distribution may result from gene flow and\/or natural selection.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n6.3 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- Name the 18th century taxonomist that classified virtually all known living things.<\/li>\n
- Describe the typological approach to classifying human variation.<\/li>\n
- Discuss why typological classifications of Homo sapiens <\/em>are associated with racism.<\/li>\n
- Why is the breeding population considered to be the most meaningful biological group?<\/li>\n
- Explain why it is generally unrealistic to apply a populational approach to classifying the human species.<\/li>\n
- What does a clinal map show?<\/li>\n
- Explain how gene flow and natural selection can result in a gradual change in the frequency of a trait over geographic space.<\/li>\n
- Most human traits vary on a continuum. Explain why this presents a problem for the typological classification approach.<\/li>\n
- \n\n
Chapter Overview: Endocrine System<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nIn this chapter, you will learn about the endocrine system, a system of glands that secrete hormones that regulate many of the body\u2019s functions. Specifically, you will learn about:\r\n\r\n \t- The [pb_glossary id=\"2936\"]glands[\/pb_glossary] that make up the [pb_glossary id=\"5985\"]endocrine system[\/pb_glossary], and how [pb_glossary id=\"5661\"]hormone[\/pb_glossary]s act as chemical messengers in the body.<\/li>\r\n \t
- The general types of endocrine system disorders.<\/li>\r\n \t
- The types of endocrine hormones \u2014 including steroid hormones (such as sex hormones) and non-steroid hormones (such as insulin) \u2014 and how they affect the functions of their target cells by binding to different types of receptor proteins.<\/li>\r\n \t
- How the levels of hormones are regulated mostly through negative, but sometimes through positive, feedback loops.<\/li>\r\n \t
- The master gland of the endocrine system, the [pb_glossary id=\"2938\"]pituitary gland[\/pb_glossary], which controls other parts of the endocrine system through the hormones that it secretes, as well as how the pituitary itself is regulated by hormones secreted from the [pb_glossary id=\"2937\"]hypothalamus[\/pb_glossary] of the brain.<\/li>\r\n \t
- The [pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary] and its hormones \u2014 which regulate processes including metabolism and calcium [pb_glossary id=\"5761\"]homeostasis[\/pb_glossary] \u2014 how the thyroid is regulated, and the disorders that can occur when there are problems in thyroid hormone regulation (such as hyperthyroidism and hypothyroidism).<\/li>\r\n \t
- The [pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary], which secrete hormones that regulate processes such as metabolism, electrolyte balance, responses to stress, and reproductive functions, and the disorders that can occur when there are problems in adrenal hormone regulation, such as Cushing\u2019s syndrome and Addison\u2019s disease.<\/li>\r\n \t
- The [pb_glossary id=\"3197\"]pancreas[\/pb_glossary], which secretes hormones that regulate blood glucose levels (such as insulin), and disorders of the pancreas and its hormones, including [pb_glossary id=\"2969\"]diabetes[\/pb_glossary].<\/li>\r\n<\/ul>\r\nLater chapters in this book will discuss the glands and hormones involved in the reproductive and immune systems in more depth.\r\n\r\n<\/div>\r\n<\/div>\r\n\r\n\r\nAs you read this chapter, think about the following questions:\r\n
\r\n \t- Why can hormones have such broad range effects on the body, as we see in PCOS?<\/li>\r\n \t
- Which hormones normally regulate blood glucose? How is this related to diabetes?<\/li>\r\n \t
- What are androgens? How do you think their functions relate to some of the symptoms that Gabrielle is experiencing?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
Attribution<\/h2>\r\nFigure 9.1.1<\/strong>\r\n\r\nChapter 9 case study<\/a> [photo] by niklas_hamann<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReference<\/h2>\r\n
Mayo Clinic Staff. (n.d.). Polycystic ovary syndrome [online article]. MayoClinic.com. https:\/\/www.mayoclinic.org\/diseases-conditions\/pcos\/multimedia\/polycystic-ovary-syndrome\/img-20007768<\/p>","rendered":"
<\/p>\nFigure 9.1.1 Could this woman have PCOS?<\/em><\/figcaption><\/figure>\n\nCase Study: Hormonal Havoc<\/h1>\n<\/div>\n
Eighteen-year-old Gabrielle checks her calendar. It has been 42 days since her last menstrual period, which is two weeks longer\u00a0than the length of the average woman\u2019s menstrual cycle. Although many women would suspect pregnancy if their period was late, Gabrielle has not been sexually active. She is not even sure she is \u201clate,\u201d because her period has never been regular. Ever since her first period\u00a0when she was 13 years old, her cycle lengths have varied greatly, and there are months where she does not get a period at all. Her mother told her that a girl\u2019s period is often irregular when it first starts, but five years later, Gabrielle\u2019s still has not become regular. She decides to go to the student health center on her college campus to get it checked out.<\/p>\n
The doctor asks her about the timing of her menstrual periods and performs a pelvic exam. She also notices that Gabrielle is overweight, has acne, and excess facial hair. As she explains to Gabrielle, while these physical characteristics can be perfectly normal, in combination with an irregular period, they can be signs of a disorder of the endocrine \u2014 or hormonal \u2014 system called polycystic ovary syndrome<\/a> (PCOS).<\/p>\nIn order to check for PCOS, the doctor refers Gabrielle for a pelvic ultrasound and sends her to the lab to get blood work done. When her lab results come back, Gabrielle learns that her levels of androgens (a group of hormones) are high, and so is her blood glucose (sugar). The ultrasound showed that she has multiple fluid-filled sacs (known as cysts) in her ovaries. Based on Gabrielle\u2019s symptoms and test results, the doctor tells her that she does indeed have PCOS.<\/p>\n
PCOS is common in young women. It is estimated that 6-10% women of childbearing age have PCOS \u2014 as many as 1.4 million women in in Canada. You may know someone with PCOS, or you may have it yourself.<\/p>\n
Read the rest of this chapter to learn about the glands and hormones of the endocrine system, their functions, how they are regulated, and the disorders \u00ad\u00ad\u2014 such as PCOS \u00ad\u00ad\u2014 that can arise when hormones are not regulated properly. At the end of the chapter, you will learn more about PCOS, its possible long-term consequences (including fertility problems and diabetes), and how these negative outcomes can sometimes be prevented with lifestyle changes and medications.<\/p>\n
\n\n\nChapter Overview: Endocrine System<\/span><\/h1>\n<\/header>\n\nIn this chapter, you will learn about the endocrine system, a system of glands that secrete hormones that regulate many of the body\u2019s functions. Specifically, you will learn about:<\/p>\n
\n- The glands<\/a> that make up the endocrine system<\/a>, and how hormone<\/a>s act as chemical messengers in the body.<\/li>\n
- The general types of endocrine system disorders.<\/li>\n
- The types of endocrine hormones \u2014 including steroid hormones (such as sex hormones) and non-steroid hormones (such as insulin) \u2014 and how they affect the functions of their target cells by binding to different types of receptor proteins.<\/li>\n
- How the levels of hormones are regulated mostly through negative, but sometimes through positive, feedback loops.<\/li>\n
- The master gland of the endocrine system, the pituitary gland<\/a>, which controls other parts of the endocrine system through the hormones that it secretes, as well as how the pituitary itself is regulated by hormones secreted from the hypothalamus<\/a> of the brain.<\/li>\n
- The thyroid gland<\/a> and its hormones \u2014 which regulate processes including metabolism and calcium homeostasis<\/a> \u2014 how the thyroid is regulated, and the disorders that can occur when there are problems in thyroid hormone regulation (such as hyperthyroidism and hypothyroidism).<\/li>\n
- The adrenal glands<\/a>, which secrete hormones that regulate processes such as metabolism, electrolyte balance, responses to stress, and reproductive functions, and the disorders that can occur when there are problems in adrenal hormone regulation, such as Cushing\u2019s syndrome and Addison\u2019s disease.<\/li>\n
- The pancreas<\/a>, which secretes hormones that regulate blood glucose levels (such as insulin), and disorders of the pancreas and its hormones, including diabetes<\/a>.<\/li>\n<\/ul>\n
Later chapters in this book will discuss the glands and hormones involved in the reproductive and immune systems in more depth.<\/p>\n<\/div>\n<\/div>\n
\nAs you read this chapter, think about the following questions:<\/p>\n
\n- Why can hormones have such broad range effects on the body, as we see in PCOS?<\/li>\n
- Which hormones normally regulate blood glucose? How is this related to diabetes?<\/li>\n
- What are androgens? How do you think their functions relate to some of the symptoms that Gabrielle is experiencing?<\/li>\n<\/ol>\n<\/div>\n<\/div>\n
Attribution<\/h2>\n
Figure 9.1.1<\/strong><\/p>\nChapter 9 case study<\/a> [photo] by niklas_hamann<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\nReference<\/h2>\n
Mayo Clinic Staff. (n.d.). Polycystic ovary syndrome [online article]. MayoClinic.com. https:\/\/www.mayoclinic.org\/diseases-conditions\/pcos\/multimedia\/polycystic-ovary-syndrome\/img-20007768<\/p>\n
definition<\/span>Created by: CK-12\/Adapted by Christine Miller<\/p>\n
\n<\/div>\n<\/div>\nFigure 6.3.1 How would you classify these people?\u00a0<\/em><\/p>\nWhy Classify?<\/h1>\n
What do you see when you look at Figure 6.3.1? Did you sort individuals into categories based in gender, age, body type, facial features, skin colour or other characteristics?\u00a0 As humans, we seem to have a penchant for classifying and labeling people and things. It helps us establish a sense of order in the world around us. The 18th century taxonomist Carl Linnaeus<\/a>, for example, classified virtually all known living things into different species, genera, families, and other taxonomic categories. His classifications were based on observable phenotypic characteristics, such as skin colour. Modern biological classifications of living things are usually based on phylogenetic relationships. Phylogenies reflect evolutionary history and group together living things that are related by descent from a common ancestor.<\/p>\nStarting with Linnaeus and continuing to the present, scientists and others have attempted to classify human variation. There are three basic approaches to classification: typological, populational, and clinal.<\/p>\n
\nTypological Approach<\/h2>\n<\/div>\n
The\u00a0typological approach\u00a0involves creating a\u00a0typology<\/a>,<\/strong>\u00a0which is a system of discrete types, or categories. This approach was widely used by scientists up through the early 20th century. Racial classifications are typological classifications. They place people into a small number of discrete categories, or\u00a0races,<\/strong> based on a few readily observable traits, such as skin colour, hair texture, facial features, and body build.<\/p>\nRacial Classifications and Racism<\/h2>\n
Racial classifications of humans probably go back as long as people distinguished \u201cus\u201d from \u201cthem.\u201d An early \u201cscientific\u201d classification of humans into races is Linnaeus\u2019 1735 classification. He divided\u00a0Homo sapiens<\/em>\u00a0into continental races, which he named\u00a0europaeus, asiaticus, americanus,<\/em>\u00a0and\u00a0afer.<\/em> Linnaeus described these races in terms of observable physical traits. He also associated, inaccurately, each race with different personality qualities and behaviors. For example, he described Homo sapiens europaeus<\/em>\u00a0as active and adventurous and\u00a0Homo sapiens afer<\/em>\u00a0as lazy and careless. In 1795, the German naturalist Johann Friedrich Blumenbach<\/a> proposed five major races of\u00a0Homo sapiens<\/em>, which he named the caucasoid, mongoloid, negroid, American Indian, and Malayan races. Blumenbach thought that the caucasoid race was the original race, and that the other races arose in a process of \u201cdegeneration\u201d from the caucasoids.<\/p>\nFigure 6.3.2 Huxley proposed that humans were categorized into nine races, and distributed geographically as shown in this map. Each colour represents one of Huxley\u2019s proposed races. These categories included \u201cAustraloid,\u201d \u201cXanthochroi,\u201d \u201cMelanochori,\u201d \u201cNegroes,\u201d and \u201cMongoloids,\u201d and they are not used today.<\/em><\/figcaption><\/figure>\nIn 1870, the English biologist Thomas Huxley<\/a> classified\u00a0Homo sapiens<\/em> into nine races which were distributed geographically<\/span>. The map in Figure 6.3.2 shows how Huxley thought the races were distributed worldwide. Each colour represents one of Huxley\u2019s proposed races. These categories included \u201cAustraloid,\u201d \u201cXanthochroi,\u201d \u201cMelanochori,\u201d \u201cNegroes,\u201d and \u201cMongoloids,\u201d and they are not used today. <\/span>It should be noted that Huxley did not hold such strong negative stereotypes about non-European (or non-caucasoid) races as did his intellectual forebears. Huxley, however, still attributed different behaviors to racial groups that had nothing to do with the colour of their skin or continent of origin.<\/p>\nBy the early 20th century, so-called\u00a0scientific racism<\/a><\/strong> was a popular ideology. This was the idea that race is a biological concept and that human behavior is partly determined by race. At around 1950, in a series of groundbreaking studies of skeletal anatomy, anthropologist Franz Boas<\/a> showed that cranial (skull) shape and size were highly malleable, depending on environmental factors (such as health and nutrition). He contrasted this with\u00a0racial anthropologists'\u00a0claims that head shape is a stable racial trait. In this way, Boas demonstrated that this commonly used racial trait was determined by the environment, and not just genes. Boas also worked to demonstrate that differences in human behavior are not determined primarily by innate biological dispositions, but are largely the result of cultural differences acquired through social learning.<\/p>\nUnfortunately,\u00a0racism<\/a><\/strong> still persists today \u2014 in society at large, if not in science. This is the association of racial traits (such as skin colour) with unrelated traits (such as intelligence), often leading to prejudice and discrimination against people based only on how they look. The concept of human race is real, not in a biological sense, but in a social sense. Racial stereotypes and racism are deeply ingrained in our history and culture, and they have real material effects on human lives.<\/p>\nAdditional Problems with Typological Classification<\/h2>\n
Besides the problem of racism, there are other problems with typological approaches to the biological classification of\u00a0Homo sapiens.<\/em>\u00a0One problem is that most human biological traits are not either present or absent, but instead vary on a continuum. This type of distribution cannot be adequately represented by discrete categories, such as races. The typological approach also results in groupings of people that may be similar in terms of some traits, but not others. How people are grouped together depends on which traits are chosen. In addition, the number of groups that are needed to classify people depends on the number of traits that are used. The greater the number of traits, the greater the number of racial categories there must be. If racial categories depend on the traits chosen to define them, it is clear that the racial classifications are arbitrary and do not reflect biological reality.<\/p>\nAnother problem with typological classifications is that they lead to the mistaken belief that people within typological categories are more similar to each other than they are to people in other categories. There is actually more variation\u00a0within<\/em>\u00a0than\u00a0between<\/em> typological groups. An estimated 90 per cent of human genetic variation occurs between people within races, and only 10 per cent occurs between races. Clearly, races are far from homogenous in terms of their genetic composition. In short, we are all more alike than we are different.<\/p>\n\nPopulational Approach<\/h1>\n<\/div>\n
By the middle of the 20th century, scientists started advocating a\u00a0populational approach<\/strong>\u00a0to classifying\u00a0Homo sapiens.<\/em>\u00a0This approach is based on the idea that the breeding population is the only biologically meaningful group. The\u00a0breeding population<\/a><\/strong>\u00a0is the unit of evolution, and it includes people who have mated and produced offspring together for many generations. As a result, members of the same breeding population should share many genetic traits. You would also expect them to have many of the same phenotypic traits, because of their similar genetic makeup.<\/p>\nWhile the populational approach makes sense in theory, in reality, it can rarely be applied, because most human populations are not closed breeding populations. Some people have always selected mates from outside their local population (even mating with archaic humans such as Neanderthals). This tendency has increased dramatically in recent centuries with the advent of efficient means of traveling long distances. As a consequence, there are very few remaining distinct breeding populations within the human species.<\/p>\nFigure 6.3.3 The Andaman Islands are boxed in red on this map of South and Southeast Asia.<\/em><\/figcaption><\/figure>\nAn example of one such population is the Sentinelese<\/a>, a small population of hunter-gatherers who live alone on a small island in the Andaman Islands (see the map). The Sentinelese are thought to be direct descendants of the first modern humans to leave Africa, and they may have lived in the Andaman Islands for as long as 60 thousand years. The Sentinelese are also one of the most isolated human populations on Earth. The fact that their language is distinctly different from other Andaman Islands languages is evidence that they have had little contact with other people for thousands of years. Although closed breeding populations (such as the Sentinelese) may be useful for investigating questions about evolutionary processes, they are not useful for classifying most of humanity.<\/p>\n <\/p>\n
\nClinal Approach<\/span><\/p>\n<\/div>\nBy the 1960s, scientists began to use a\u00a0clinal approach<\/strong>\u00a0to classify human variation. This approach maps variation in traits over geographic regions (such as continents) or even worldwide. Clinal models are a useful way of describing human variation that does not lead to discrete races or other categories of people.<\/p>\nFigure 6.3.4 Distribution of Type O Blood in Indigenous Populations of the World.<\/em><\/figcaption><\/figure>\nIn Figure 6.3.4 you can see a worldwide clinal map for type O blood in the human ABO blood group system. The frequency of this trait is shown for the indigenous populations of various regions. It is lowest throughout Asia and highest in Native American populations in both North and South America. This geographic distribution results from the complex interaction of a variety of factors, including natural selection, genetic drift, and gene flow. You can read more about geographic variation in blood types in the concept Variation in Blood Types.<\/em><\/p>\n\nClinal maps for many genetic traits show variation that changes gradually from one geographic area to another, which may happen because of the nature of gene flow. Gene flow occurs when mating takes place between people in different populations. The likelihood of mating with others depends on their distance from us. You may not marry the boy or girl next door, but your mate is more likely to be someone in the same state or country than someone on another continent.<\/span><\/p>\n<\/div>\nNatural selection has a major impact on the clinal distribution of some traits, because variation in the traits tracks variation in selective pressures. For example, the environmental stressor of malaria varies throughout Africa with climate, as you can see in the left-hand map below (Figure 6.3.5). The sickle cell trait that protects from malaria has a similar distribution, as shown in the right-hand map.<\/p>\n
\n<\/div>\n<\/div>\nFigure 6.3.5\u00a0<\/em><\/p>\n\n\n6.3 Summary<\/span><\/h1>\n<\/header>\n\n\n- Humans seem to have a need to classify<\/a> and label people based on their similarities and differences. Three approaches to classifying human variation include typological, populational, and clinal approaches.<\/li>\n
- The typological approach involves creating a typology, which is a system of discrete categories, or races. This approach was widely used by scientists until the early 20th century. Racial categories are based on observable phenotypic traits (such as skin colour), but other traits and behaviors are often assumed to apply to racial groups, as well. The use of racial classifications often leads to racism<\/a>.<\/li>\n
- By the mid-20th century, scientists started advocating a population approach. This assumes that the breeding population, which is the unit of evolution, is the only biologically meaningful group. While this approach makes sense in theory, in reality, it can rarely be applied to actual human populations. With few exceptions, most human populations are not closed breeding populations.<\/li>\n
- By the 1960s, scientists began to use a clinal approach to classify human variation. This approach maps variation in the frequency of traits or alleles over geographic regions or worldwide. Clinal maps for many genetic traits show variation that changes gradually from one geographic area to another. This type of distribution may result from gene flow and\/or natural selection.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n6.3 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- Name the 18th century taxonomist that classified virtually all known living things.<\/li>\n
- Describe the typological approach to classifying human variation.<\/li>\n
- Discuss why typological classifications of Homo sapiens <\/em>are associated with racism.<\/li>\n
- Why is the breeding population considered to be the most meaningful biological group?<\/li>\n
- Explain why it is generally unrealistic to apply a populational approach to classifying the human species.<\/li>\n
- What does a clinal map show?<\/li>\n
- Explain how gene flow and natural selection can result in a gradual change in the frequency of a trait over geographic space.<\/li>\n
- Most human traits vary on a continuum. Explain why this presents a problem for the typological classification approach.<\/li>\n
- \n\n
- \r\n \t
- The [pb_glossary id=\"2936\"]glands[\/pb_glossary] that make up the [pb_glossary id=\"5985\"]endocrine system[\/pb_glossary], and how [pb_glossary id=\"5661\"]hormone[\/pb_glossary]s act as chemical messengers in the body.<\/li>\r\n \t
- The general types of endocrine system disorders.<\/li>\r\n \t
- The types of endocrine hormones \u2014 including steroid hormones (such as sex hormones) and non-steroid hormones (such as insulin) \u2014 and how they affect the functions of their target cells by binding to different types of receptor proteins.<\/li>\r\n \t
- How the levels of hormones are regulated mostly through negative, but sometimes through positive, feedback loops.<\/li>\r\n \t
- The master gland of the endocrine system, the [pb_glossary id=\"2938\"]pituitary gland[\/pb_glossary], which controls other parts of the endocrine system through the hormones that it secretes, as well as how the pituitary itself is regulated by hormones secreted from the [pb_glossary id=\"2937\"]hypothalamus[\/pb_glossary] of the brain.<\/li>\r\n \t
- The [pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary] and its hormones \u2014 which regulate processes including metabolism and calcium [pb_glossary id=\"5761\"]homeostasis[\/pb_glossary] \u2014 how the thyroid is regulated, and the disorders that can occur when there are problems in thyroid hormone regulation (such as hyperthyroidism and hypothyroidism).<\/li>\r\n \t
- The [pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary], which secrete hormones that regulate processes such as metabolism, electrolyte balance, responses to stress, and reproductive functions, and the disorders that can occur when there are problems in adrenal hormone regulation, such as Cushing\u2019s syndrome and Addison\u2019s disease.<\/li>\r\n \t
- The [pb_glossary id=\"3197\"]pancreas[\/pb_glossary], which secretes hormones that regulate blood glucose levels (such as insulin), and disorders of the pancreas and its hormones, including [pb_glossary id=\"2969\"]diabetes[\/pb_glossary].<\/li>\r\n<\/ul>\r\nLater chapters in this book will discuss the glands and hormones involved in the reproductive and immune systems in more depth.\r\n\r\n<\/div>\r\n<\/div>\r\n\r\n\r\nAs you read this chapter, think about the following questions:\r\n
- \r\n \t
- Why can hormones have such broad range effects on the body, as we see in PCOS?<\/li>\r\n \t
- Which hormones normally regulate blood glucose? How is this related to diabetes?<\/li>\r\n \t
- What are androgens? How do you think their functions relate to some of the symptoms that Gabrielle is experiencing?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
Attribution<\/h2>\r\nFigure 9.1.1<\/strong>\r\n\r\nChapter 9 case study<\/a> [photo] by niklas_hamann<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n
Reference<\/h2>\r\n
Mayo Clinic Staff. (n.d.). Polycystic ovary syndrome [online article]. MayoClinic.com. https:\/\/www.mayoclinic.org\/diseases-conditions\/pcos\/multimedia\/polycystic-ovary-syndrome\/img-20007768<\/p>","rendered":"
<\/p>\n
Figure 9.1.1 Could this woman have PCOS?<\/em><\/figcaption><\/figure>\n \nCase Study: Hormonal Havoc<\/h1>\n<\/div>\n
Eighteen-year-old Gabrielle checks her calendar. It has been 42 days since her last menstrual period, which is two weeks longer\u00a0than the length of the average woman\u2019s menstrual cycle. Although many women would suspect pregnancy if their period was late, Gabrielle has not been sexually active. She is not even sure she is \u201clate,\u201d because her period has never been regular. Ever since her first period\u00a0when she was 13 years old, her cycle lengths have varied greatly, and there are months where she does not get a period at all. Her mother told her that a girl\u2019s period is often irregular when it first starts, but five years later, Gabrielle\u2019s still has not become regular. She decides to go to the student health center on her college campus to get it checked out.<\/p>\n
The doctor asks her about the timing of her menstrual periods and performs a pelvic exam. She also notices that Gabrielle is overweight, has acne, and excess facial hair. As she explains to Gabrielle, while these physical characteristics can be perfectly normal, in combination with an irregular period, they can be signs of a disorder of the endocrine \u2014 or hormonal \u2014 system called polycystic ovary syndrome<\/a> (PCOS).<\/p>\n
In order to check for PCOS, the doctor refers Gabrielle for a pelvic ultrasound and sends her to the lab to get blood work done. When her lab results come back, Gabrielle learns that her levels of androgens (a group of hormones) are high, and so is her blood glucose (sugar). The ultrasound showed that she has multiple fluid-filled sacs (known as cysts) in her ovaries. Based on Gabrielle\u2019s symptoms and test results, the doctor tells her that she does indeed have PCOS.<\/p>\n
PCOS is common in young women. It is estimated that 6-10% women of childbearing age have PCOS \u2014 as many as 1.4 million women in in Canada. You may know someone with PCOS, or you may have it yourself.<\/p>\n
Read the rest of this chapter to learn about the glands and hormones of the endocrine system, their functions, how they are regulated, and the disorders \u00ad\u00ad\u2014 such as PCOS \u00ad\u00ad\u2014 that can arise when hormones are not regulated properly. At the end of the chapter, you will learn more about PCOS, its possible long-term consequences (including fertility problems and diabetes), and how these negative outcomes can sometimes be prevented with lifestyle changes and medications.<\/p>\n
\n\n\n Chapter Overview: Endocrine System<\/span><\/h1>\n<\/header>\n
\nIn this chapter, you will learn about the endocrine system, a system of glands that secrete hormones that regulate many of the body\u2019s functions. Specifically, you will learn about:<\/p>\n
- \n
- The glands<\/a> that make up the endocrine system<\/a>, and how hormone<\/a>s act as chemical messengers in the body.<\/li>\n
- The general types of endocrine system disorders.<\/li>\n
- The types of endocrine hormones \u2014 including steroid hormones (such as sex hormones) and non-steroid hormones (such as insulin) \u2014 and how they affect the functions of their target cells by binding to different types of receptor proteins.<\/li>\n
- How the levels of hormones are regulated mostly through negative, but sometimes through positive, feedback loops.<\/li>\n
- The master gland of the endocrine system, the pituitary gland<\/a>, which controls other parts of the endocrine system through the hormones that it secretes, as well as how the pituitary itself is regulated by hormones secreted from the hypothalamus<\/a> of the brain.<\/li>\n
- The thyroid gland<\/a> and its hormones \u2014 which regulate processes including metabolism and calcium homeostasis<\/a> \u2014 how the thyroid is regulated, and the disorders that can occur when there are problems in thyroid hormone regulation (such as hyperthyroidism and hypothyroidism).<\/li>\n
- The adrenal glands<\/a>, which secrete hormones that regulate processes such as metabolism, electrolyte balance, responses to stress, and reproductive functions, and the disorders that can occur when there are problems in adrenal hormone regulation, such as Cushing\u2019s syndrome and Addison\u2019s disease.<\/li>\n
- The pancreas<\/a>, which secretes hormones that regulate blood glucose levels (such as insulin), and disorders of the pancreas and its hormones, including diabetes<\/a>.<\/li>\n<\/ul>\n
Later chapters in this book will discuss the glands and hormones involved in the reproductive and immune systems in more depth.<\/p>\n<\/div>\n<\/div>\n
\nAs you read this chapter, think about the following questions:<\/p>\n
- \n
- Why can hormones have such broad range effects on the body, as we see in PCOS?<\/li>\n
- Which hormones normally regulate blood glucose? How is this related to diabetes?<\/li>\n
- What are androgens? How do you think their functions relate to some of the symptoms that Gabrielle is experiencing?<\/li>\n<\/ol>\n<\/div>\n<\/div>\n
Attribution<\/h2>\n
Figure 9.1.1<\/strong><\/p>\n
Chapter 9 case study<\/a> [photo] by niklas_hamann<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\n
Reference<\/h2>\n
Mayo Clinic Staff. (n.d.). Polycystic ovary syndrome [online article]. MayoClinic.com. https:\/\/www.mayoclinic.org\/diseases-conditions\/pcos\/multimedia\/polycystic-ovary-syndrome\/img-20007768<\/p>\n
definition<\/span>Created by: CK-12\/Adapted by Christine Miller<\/p>\n
\n<\/div>\n<\/div>\nFigure 6.3.1 How would you classify these people?\u00a0<\/em><\/p>\n
Why Classify?<\/h1>\n
What do you see when you look at Figure 6.3.1? Did you sort individuals into categories based in gender, age, body type, facial features, skin colour or other characteristics?\u00a0 As humans, we seem to have a penchant for classifying and labeling people and things. It helps us establish a sense of order in the world around us. The 18th century taxonomist Carl Linnaeus<\/a>, for example, classified virtually all known living things into different species, genera, families, and other taxonomic categories. His classifications were based on observable phenotypic characteristics, such as skin colour. Modern biological classifications of living things are usually based on phylogenetic relationships. Phylogenies reflect evolutionary history and group together living things that are related by descent from a common ancestor.<\/p>\n
Starting with Linnaeus and continuing to the present, scientists and others have attempted to classify human variation. There are three basic approaches to classification: typological, populational, and clinal.<\/p>\n
\nTypological Approach<\/h2>\n<\/div>\n
The\u00a0typological approach\u00a0involves creating a\u00a0typology<\/a>,<\/strong>\u00a0which is a system of discrete types, or categories. This approach was widely used by scientists up through the early 20th century. Racial classifications are typological classifications. They place people into a small number of discrete categories, or\u00a0races,<\/strong> based on a few readily observable traits, such as skin colour, hair texture, facial features, and body build.<\/p>\n
Racial Classifications and Racism<\/h2>\n
Racial classifications of humans probably go back as long as people distinguished \u201cus\u201d from \u201cthem.\u201d An early \u201cscientific\u201d classification of humans into races is Linnaeus\u2019 1735 classification. He divided\u00a0Homo sapiens<\/em>\u00a0into continental races, which he named\u00a0europaeus, asiaticus, americanus,<\/em>\u00a0and\u00a0afer.<\/em> Linnaeus described these races in terms of observable physical traits. He also associated, inaccurately, each race with different personality qualities and behaviors. For example, he described Homo sapiens europaeus<\/em>\u00a0as active and adventurous and\u00a0Homo sapiens afer<\/em>\u00a0as lazy and careless. In 1795, the German naturalist Johann Friedrich Blumenbach<\/a> proposed five major races of\u00a0Homo sapiens<\/em>, which he named the caucasoid, mongoloid, negroid, American Indian, and Malayan races. Blumenbach thought that the caucasoid race was the original race, and that the other races arose in a process of \u201cdegeneration\u201d from the caucasoids.<\/p>\n
Figure 6.3.2 Huxley proposed that humans were categorized into nine races, and distributed geographically as shown in this map. Each colour represents one of Huxley\u2019s proposed races. These categories included \u201cAustraloid,\u201d \u201cXanthochroi,\u201d \u201cMelanochori,\u201d \u201cNegroes,\u201d and \u201cMongoloids,\u201d and they are not used today.<\/em><\/figcaption><\/figure>\n In 1870, the English biologist Thomas Huxley<\/a> classified\u00a0Homo sapiens<\/em> into nine races which were distributed geographically<\/span>. The map in Figure 6.3.2 shows how Huxley thought the races were distributed worldwide. Each colour represents one of Huxley\u2019s proposed races. These categories included \u201cAustraloid,\u201d \u201cXanthochroi,\u201d \u201cMelanochori,\u201d \u201cNegroes,\u201d and \u201cMongoloids,\u201d and they are not used today. <\/span>It should be noted that Huxley did not hold such strong negative stereotypes about non-European (or non-caucasoid) races as did his intellectual forebears. Huxley, however, still attributed different behaviors to racial groups that had nothing to do with the colour of their skin or continent of origin.<\/p>\n
By the early 20th century, so-called\u00a0scientific racism<\/a><\/strong> was a popular ideology. This was the idea that race is a biological concept and that human behavior is partly determined by race. At around 1950, in a series of groundbreaking studies of skeletal anatomy, anthropologist Franz Boas<\/a> showed that cranial (skull) shape and size were highly malleable, depending on environmental factors (such as health and nutrition). He contrasted this with\u00a0racial anthropologists'\u00a0claims that head shape is a stable racial trait. In this way, Boas demonstrated that this commonly used racial trait was determined by the environment, and not just genes. Boas also worked to demonstrate that differences in human behavior are not determined primarily by innate biological dispositions, but are largely the result of cultural differences acquired through social learning.<\/p>\n
Unfortunately,\u00a0racism<\/a><\/strong> still persists today \u2014 in society at large, if not in science. This is the association of racial traits (such as skin colour) with unrelated traits (such as intelligence), often leading to prejudice and discrimination against people based only on how they look. The concept of human race is real, not in a biological sense, but in a social sense. Racial stereotypes and racism are deeply ingrained in our history and culture, and they have real material effects on human lives.<\/p>\n
Additional Problems with Typological Classification<\/h2>\n
Besides the problem of racism, there are other problems with typological approaches to the biological classification of\u00a0Homo sapiens.<\/em>\u00a0One problem is that most human biological traits are not either present or absent, but instead vary on a continuum. This type of distribution cannot be adequately represented by discrete categories, such as races. The typological approach also results in groupings of people that may be similar in terms of some traits, but not others. How people are grouped together depends on which traits are chosen. In addition, the number of groups that are needed to classify people depends on the number of traits that are used. The greater the number of traits, the greater the number of racial categories there must be. If racial categories depend on the traits chosen to define them, it is clear that the racial classifications are arbitrary and do not reflect biological reality.<\/p>\n
Another problem with typological classifications is that they lead to the mistaken belief that people within typological categories are more similar to each other than they are to people in other categories. There is actually more variation\u00a0within<\/em>\u00a0than\u00a0between<\/em> typological groups. An estimated 90 per cent of human genetic variation occurs between people within races, and only 10 per cent occurs between races. Clearly, races are far from homogenous in terms of their genetic composition. In short, we are all more alike than we are different.<\/p>\n
\nPopulational Approach<\/h1>\n<\/div>\n
By the middle of the 20th century, scientists started advocating a\u00a0populational approach<\/strong>\u00a0to classifying\u00a0Homo sapiens.<\/em>\u00a0This approach is based on the idea that the breeding population is the only biologically meaningful group. The\u00a0breeding population<\/a><\/strong>\u00a0is the unit of evolution, and it includes people who have mated and produced offspring together for many generations. As a result, members of the same breeding population should share many genetic traits. You would also expect them to have many of the same phenotypic traits, because of their similar genetic makeup.<\/p>\n
While the populational approach makes sense in theory, in reality, it can rarely be applied, because most human populations are not closed breeding populations. Some people have always selected mates from outside their local population (even mating with archaic humans such as Neanderthals). This tendency has increased dramatically in recent centuries with the advent of efficient means of traveling long distances. As a consequence, there are very few remaining distinct breeding populations within the human species.<\/p>\n
Figure 6.3.3 The Andaman Islands are boxed in red on this map of South and Southeast Asia.<\/em><\/figcaption><\/figure>\n An example of one such population is the Sentinelese<\/a>, a small population of hunter-gatherers who live alone on a small island in the Andaman Islands (see the map). The Sentinelese are thought to be direct descendants of the first modern humans to leave Africa, and they may have lived in the Andaman Islands for as long as 60 thousand years. The Sentinelese are also one of the most isolated human populations on Earth. The fact that their language is distinctly different from other Andaman Islands languages is evidence that they have had little contact with other people for thousands of years. Although closed breeding populations (such as the Sentinelese) may be useful for investigating questions about evolutionary processes, they are not useful for classifying most of humanity.<\/p>\n
<\/p>\n
\nClinal Approach<\/span><\/p>\n<\/div>\n
By the 1960s, scientists began to use a\u00a0clinal approach<\/strong>\u00a0to classify human variation. This approach maps variation in traits over geographic regions (such as continents) or even worldwide. Clinal models are a useful way of describing human variation that does not lead to discrete races or other categories of people.<\/p>\n
Figure 6.3.4 Distribution of Type O Blood in Indigenous Populations of the World.<\/em><\/figcaption><\/figure>\n In Figure 6.3.4 you can see a worldwide clinal map for type O blood in the human ABO blood group system. The frequency of this trait is shown for the indigenous populations of various regions. It is lowest throughout Asia and highest in Native American populations in both North and South America. This geographic distribution results from the complex interaction of a variety of factors, including natural selection, genetic drift, and gene flow. You can read more about geographic variation in blood types in the concept Variation in Blood Types.<\/em><\/p>\n
\nClinal maps for many genetic traits show variation that changes gradually from one geographic area to another, which may happen because of the nature of gene flow. Gene flow occurs when mating takes place between people in different populations. The likelihood of mating with others depends on their distance from us. You may not marry the boy or girl next door, but your mate is more likely to be someone in the same state or country than someone on another continent.<\/span><\/p>\n<\/div>\n
Natural selection has a major impact on the clinal distribution of some traits, because variation in the traits tracks variation in selective pressures. For example, the environmental stressor of malaria varies throughout Africa with climate, as you can see in the left-hand map below (Figure 6.3.5). The sickle cell trait that protects from malaria has a similar distribution, as shown in the right-hand map.<\/p>\n
\n<\/div>\n<\/div>\nFigure 6.3.5\u00a0<\/em><\/p>\n
\n\n 6.3 Summary<\/span><\/h1>\n<\/header>\n
\n- \n
- Humans seem to have a need to classify<\/a> and label people based on their similarities and differences. Three approaches to classifying human variation include typological, populational, and clinal approaches.<\/li>\n
- The typological approach involves creating a typology, which is a system of discrete categories, or races. This approach was widely used by scientists until the early 20th century. Racial categories are based on observable phenotypic traits (such as skin colour), but other traits and behaviors are often assumed to apply to racial groups, as well. The use of racial classifications often leads to racism<\/a>.<\/li>\n
- By the mid-20th century, scientists started advocating a population approach. This assumes that the breeding population, which is the unit of evolution, is the only biologically meaningful group. While this approach makes sense in theory, in reality, it can rarely be applied to actual human populations. With few exceptions, most human populations are not closed breeding populations.<\/li>\n
- By the 1960s, scientists began to use a clinal approach to classify human variation. This approach maps variation in the frequency of traits or alleles over geographic regions or worldwide. Clinal maps for many genetic traits show variation that changes gradually from one geographic area to another. This type of distribution may result from gene flow and\/or natural selection.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n
\n\n 6.3 Review Questions<\/span><\/h1>\n<\/header>\n
\n- \n
- Name the 18th century taxonomist that classified virtually all known living things.<\/li>\n
- Describe the typological approach to classifying human variation.<\/li>\n
- Discuss why typological classifications of Homo sapiens <\/em>are associated with racism.<\/li>\n
- Why is the breeding population considered to be the most meaningful biological group?<\/li>\n
- Explain why it is generally unrealistic to apply a populational approach to classifying the human species.<\/li>\n
- What does a clinal map show?<\/li>\n
- Explain how gene flow and natural selection can result in a gradual change in the frequency of a trait over geographic space.<\/li>\n
- Most human traits vary on a continuum. Explain why this presents a problem for the typological classification approach.<\/li>\n
- \n
\n
- The typological approach involves creating a typology, which is a system of discrete categories, or races. This approach was widely used by scientists until the early 20th century. Racial categories are based on observable phenotypic traits (such as skin colour), but other traits and behaviors are often assumed to apply to racial groups, as well. The use of racial classifications often leads to racism<\/a>.<\/li>\n
- Humans seem to have a need to classify<\/a> and label people based on their similarities and differences. Three approaches to classifying human variation include typological, populational, and clinal approaches.<\/li>\n
- The glands<\/a> that make up the endocrine system<\/a>, and how hormone<\/a>s act as chemical messengers in the body.<\/li>\n