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The 7 Sexes

Biology of Sex Determination

Elof Axel Carlson

Publication Year: 2013

Few of us know much about the biology of sex determination, but what could be more interesting than to discover how we are shaped into males and females? In this book, Elof Carlson tells the incredible story of the difficult quest to understand how the body forms girls and boys. Carlson's history takes us from antiquity to the present day to detail how each component of human reproduction and sexuality was identified and studied, how this knowledge enlarged our understanding of sex determination, and how it was employed to interpret such little understood aspects of human biology as the origin of intersex births.

Published by: Indiana University Press

Title Page, Copyright, Dedication

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pp. 2-7


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pp. 8-9


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pp. ix-x


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pp. xi-xii

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pp. xiii-xv

Every aspect of the history of sexuality is controversial. Eating, fashion, sports, occupation, or political outlook can be discussed freely in public, even by those who disagree...

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1. Introduction

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pp. 1-5

With rare exceptions, animals consist of sexually reproducing populations that are roughly half male and half female—at least that is a human perspective that...

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2. Wild Guesses in an Era of Scientific Ignorance

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pp. 6-11

Almost all of the topics taught in K–12 or undergraduate introductory science courses come from work published in the last two centuries. Before the nineteenth...

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3. The Ancient World

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pp. 12-18

Cellular life, sex determination, reproduction, and the processes associated with gestation are largely unseen and unknowable without the tools of science....

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4. Monotheistic Religious Interpretations

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pp. 19-25

Countries with substantial populations of Christians and Muslims follow a monotheistic tradition derived from the Jews and their scriptures, the Old Testament or Hebrew...

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5. The Descriptive Embryology of Male and Female Development

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pp. 26-33

The study of embryology was extremely limited until the 1860s, when several techniques came together. One was the development of achromatic lenses, which...

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6. The Discovery of the Egg in Higher Eukaryotes

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pp. 34-41

While it was known to almost all of humanity since antiquity that birds lay eggs, it was not known that the egg is a cell until cell theory was developed in the 1830s...

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7. The Discovery of Sperm in Higher Eukaryotes

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pp. 42-49

Semen has long been recognized as necessary for producing offspring. It is liquid, somewhat viscous, and usually clear or slightly cloudy in appearance; certainly the unaided...

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8. The Discovery of Sex Hormones

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pp. 50-57

In 1902, William Bayliss (1860–1924) and Ernest Starling (1866–1927) introduced the term “hormone.”1 Hormones are substances produced by one organ, an endocrine...

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9. Ploidy Levels and Sex Determination

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pp. 58-62

We tend to think of all animals as being diploid, represented as 2N, and their gametes as haploid, represented as N. Exceptions are rare: this is not true for only about...

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10. The Discovery of Sex Chromosomes

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pp. 63-70

The idea of the continuity of chromosomes arose among German cytologists in the 1880s. At that time, many American biologists would get their PhDs (especially at Johns Hopkins...

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11. The Balance Theory of Sex Determination

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pp. 71-75

From 1907, when Thomas Hunt Morgan began working on fruit flies, until 1915, he and his students believed that their sex chromosome composition was...

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12. The Discovery of Sex in Microorganisms

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pp. 76-83

When Anthony van Leeuenhoek observed the animalcules, as he called them, from different dips of water or from his own body, he did not discuss how they formed...

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13. The History and Interpretations of Hermaphrodites and Intersexes

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pp. 84-95

The concepts of hermaphroditism, sexual chimerism, sexual mosaicism, intersexuality, and gynandromorphism are all connected through a common aspect. They involve...

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14. Dosage Compensation and the Sex Chromosomes

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pp. 96-103

Calvin Bridges and Thomas Hunt Morgan discovered the existence of dosage differences on the X chromosome of fruit flies when comparing the allele of white eyes called...

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15. The Discovery of Human Sex Chromosome Conditions

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pp. 104-110

When Michael Frederic Guyer (1874–1959) looked at human chromosomes in 1910, he estimated the diploid...

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16. The Seven Sexes of Humans

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pp. 111-120

In 1958, when I was a freshly minted PhD from Muller’s laboratory at Indiana University, I took my first academic job at Queen’s University in Kingston, Ontario...

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17. The Identification and Role of Sex-Determining Genes

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pp. 121-131

Life can be resilient and vulnerable at the same time. We rejoice at stories of Olympic medalists who overcome severe injury or a childhood marked with tragedy...

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18. The History of Homosexuality

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pp. 132-139

All human behavior is subject to the judgment of others. As children, we are judged by our parents, teachers, and playmates. Some behaviors are approved and admired...

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19. The History of Behavioral Gender Assignment

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pp. 140-145

Identifying genes for homosexuality is difficult, but it is even more difficult to assign a genetic or innate basis for gender roles. Why should this be so difficult? Because...

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20. The Evolution of Sex Determination

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pp. 146-153

In 1871, Charles Darwin published his long awaited Descent of Man and Selection in Relation to Sex.1 Darwin considered sexual evolution as a lesser form of natural selection and he gave it the term sexual selection. This distinction made sense...

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21. What Does It Mean to Have an Assigned Sex?

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pp. 154-158

Long before birth certificates existed, babies were assigned their sex by examination of their external genitals: a penis and scrotum defined a male; a vagina and female...

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22. The Quest for a Unified Theory of Sex, Gender, and Sexuality

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pp. 159-174

I have attempted to explore the history of sex determination. As a biologist, my outlook is comparative, because the human story was largely built from findings about...

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pp. 175-176

I wroteThe 7 Sexes before the political debates over contraceptives, abortion, and women’s health care became issues in the U.S. 2012 Presidential election. This book, from my training...

Appendix: Secondary Literature and the Relation of Biology to Sex and Gender

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pp. 177-190


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pp. 191-204


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pp. 205-224


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pp. 225-235

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About the Author

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p. 236-236

Elof Axel Carlson is a geneticist and historian of science. He received his PhD in genetics at Indiana University, studying with Nobelist H. J. Muller. Carlson is the author of 12 books, and has written a biweekly newspaper column...

E-ISBN-13: 9780253006547
E-ISBN-10: 0253006546
Print-ISBN-13: 9780253006455

Page Count: 256
Illustrations: 27 b&w illus.
Publication Year: 2013