<figure id="attachment_459653" aria-describedby="caption-attachment-459653" style="width: 640px" class="wp-caption alignnone"><a href="#" data-ident_hash="6378acff"><img src="https://res.cloudinary.com/fridaydigital/image/private/t_article_image/wpmedia/2026/03/5a269342f4a42134c3780da63a76baf7.jpg" alt=""></a><figcaption id="caption-attachment-459653" class="wp-caption-text">Why is human sex so diverse &#8230;&#8230;? (Image is for illustrative purposes only.)</figcaption></figure>
<h3><span class="strongInContent"> What is the Anthropology of Sex?</span></h3>
<p> Human sex is diverse. While many other animals have sex only during the &#8220;breeding season,&#8221; which comes in a fixed cycle, humans have sex all year round, and sometimes not at all. And the purpose is not necessarily for reproduction. Moreover, the object of sex is not always the opposite sex. Sometimes it is not even human.</p>
<p> Because it is an act that is hidden on a daily basis and basically not shared with others, the way it is done varies from person to person. Furthermore, if we look at human society as a whole, there are diverse &#8220;ways&#8221; of doing things in each unique culture.</p>
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<p> The &#8220;anthropology of sexuality&#8221; focuses on the diversity of sexuality in human society, and through fieldwork, records and examines even the breath of people&#8217;s sexual activities. However, Katsumi Okuno, an anthropologist and professor at Rikkyo University&#8217;s Faculty of Intercultural Communication, published &#8220;Anthropologists Teach Sexuality Lessons&#8221; (Hayakawa Shinsho) in December 2013, seems to take a different approach.</p>
<p> In the book, he introduces the diversity of sex in the world that anthropologists have come into contact with through their fieldwork. Societies in which pregnant women are obligated to be &#8220;second fathers&#8221; to their unborn children by having sex with men other than their husbands; societies in which people believe that bad things happen when they have sex other than for reproductive purposes; societies in which boys experience homosexuality and bisexuality as a rite of passage &#8230;&#8230;. However, merely presenting these diverse sexualities in a catalog-like format is only half of the &#8220;anthropology of sexuality,&#8221; Okuno said.</p>
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<p><span class="strongInContent"> Human beings have created cultures in diverse ways, and have created various forms of sexual activity in different lands and environments. However, humans are not the only ones who have been engaged in sexual activity, as animals and plants have also been engaged in sexual activity. I believe that looking back in history to 1.5 billion years ago, when sex was first born, will provide us with rich insights into the nature of sexual activity.</span></p>
<p> In &#8220;An Anthropologist&#8217;s Guide to Sex,&#8221; Okuno approaches sex from two perspectives: the &#8220;vertical axis,&#8221; which views the history of sex in the context of biological evolution from the past to the present, and the &#8220;horizontal axis,&#8221; which compares the various sexual cultures practiced in different parts of the world from a comparative cultural perspective.</p>
<div data-friday-nextpage-lead=" History of Sex in Biological Evolution"></div>
<h3><span class="strongInContent">Humans gained diversity through the evolution of sex.</span></h3>
<p> Before the birth of sex, life forms reproduced asexually, copying their own genes to leave the next generation. However, since the genes of each individual are all the same, the species would be wiped out if the environment changed or a virus attacked. However, in the case of individuals who inherit half of their genes from their mothers and fathers through sexual reproduction, the genetic makeup of each individual is different, so some individuals will survive even if the environment changes. According to one theory, sex may have emerged from such an evolutionary process.</p>
<p> Reproduction through sexual reproduction was advantageous for organisms to evolve in terms of adapting to the environment. Organisms engaged in a variety of sexual activities to ensure the prosperity of their species. In primates, the evolutionary process involves the male courting, the female accepting the courtship, and the male&#8217;s body size increasing.</p>
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<p> The basic pattern is that the male is excited by the female&#8217;s showing signs of estrus, such as her buttocks turning red, but the closer a species becomes to humans, the more these signs disappear. However, the closer a species becomes to humans, the more these signs disappear, Okuno says.</p>
<p><span class="strongInContent"> It is all hypothetical, but if the pattern of males becoming sexually aroused when females show signs of estrus is broken, males will have to look for other signs. Then the sex partners of gorillas and orangutans often cross sexual boundaries, because they don&#8217;t need a female to be sexually aroused.</span></p>
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<p><span class="strongInContent"> The disappearance of mating signs is also the basis for the emergence of fetishes. The sign becomes sexual arousal at the slightest difference in the other person&#8217;s gestures, voice, or a particular part of the body. In the case of humans, the personal characteristics of sexual attraction can vary, and can be anything from the voice, gestures, or various parts of the body such as the nape of the neck, breasts, or legs, to the underwear one wears or the saddle on one&#8217;s bicycle.</span></p>
<p><span class="strongInContent"> By considering humans as living beings, we can see human sexuality in the context of this one major evolutionary process.&#8221;</span></p>
<div data-friday-nextpage-lead=" Even more varied forms in culture and environment"></div>
<h3><span class="strongInContent">People Living Multiple Sexualities</span></h3>
<p> Human sex has become diverse due to the loss of the mating sign in the evolutionary process, and from there it has further divided into various forms depending on culture and environment. According to Okuno, sex has three basic functions. (1) reproduction, (2) pleasure, and (3) social regulation.</p>
<p><span class="strongInContent"> For example, the bonobo, a large ape, is said to have all three. They are very sexually active and engage in omnidirectional sex without limiting their partners, whether they are of the opposite or same sex. They use sex not only for reproduction, but also for pleasure and as a means of solving social problems.</span></p>
<p><span class="strongInContent"> They do not engage in sex as intensely as humans do, but rather touch each other&#8217;s genitalia, &#8220;butt rubbing,&#8221; in which males rub their testicles against each other, &#8220;GG rubbing,&#8221; in which females rub their genitalia against each other, and so on. and so on.</span></p>
<p><span class="strongInContent"> Sex serves a social regulating function, as it is a way to settle ruts, express affection, and greet each other. These are the original three reasons, and in the case of humans, it gets more complicated depending on the environment and culture in which we are placed.&#8221;</span></p>
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<p> One example of this is the case of the Sambian people living in highland New Guinea, which is discussed in this book. The Sambia are the people that American anthropologist Gilbert Hart introduced in &#8220;Studies in the Culture of Homosexuality&#8221; after conducting fieldwork there since 1947, a provisional name given by Hart in light of the possibility that the shocking culture of the region could lead to false understandings and representations.</p>
<p> He said that men live multiple sexualities in their lives: homosexual as boys, bisexual as adults for a while after marrying a woman, and heterosexual as fathers after ceasing to be homosexual.</p>
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<p><span class="strongInContent"> In their culture, it is believed that all people are born female, even if they are biologically male. They can acquire masculinity by injecting &#8220;masculinity&#8221; into their lives. This &#8220;masculinity&#8221; is semen, and they all engage in homosexual acts from boyhood to adulthood in order to inject the semen of older men.</span></p>
<p><span class="strongInContent"> The Sambian people are constantly at war with other tribes, and warriors are supposed to be masculine. It is thought that this &#8220;ritual homosexuality&#8221; is a system that has been created in order for them to acquire masculinity. In other words, they have developed their culture in an environment of frequent warfare.</span></p>
<div data-friday-nextpage-lead=" Is Our Sex Abnormal?"></div>
<h3><span class="strongInContent">The Need to &#8220;Turn It Over and Look at It&#8221;</span></h3>
<p> Human sex has evolved in a great variety of ways in different regions and cultures. However, the world is not always tolerant of this diversity. For example, feminists in developed Western countries have called for the abolition of female circumcision (FGM), <span class="strongInContent">saying that it is a form of sex control and a violation of human rights</span>, while women in Africa and other countries where female circumcision is practiced have protested <span class="strongInContent">, saying that they do not want their culture to be criticized</span>. This is a very common example. LGBTQ prejudice still persists everywhere, to cite a more prosaic example.</p>
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<p><span class="strongInContent"> &#8220;If something is not what you think is normal, you try to dismiss it as &#8216;abnormal,'&#8221; said one woman. Or there is a kind of phobia or aversion to things like LGBTQ. It comes from being obsessed with something. As you study the anthropology of sexuality, you realize what you are trapped in, and at some point, you are convinced, &#8216;Oh, there is such a way of being sexual.</span></p>
<p><span class="strongInContent"> If you learn about the various ways of sexual activity that humanity has developed, you will realize that our sex is just one of them, and that there are other ways that we consider abnormal, such as the way of the people of Sambia. In other words, I think it is important to turn your own norm upside down and look at it, and realize that you are trapped in it.</span></p>
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<p> On the contrary, Sambians say they do not understand &#8220;gay&#8221; and &#8220;lesbian. In our society, it is a common term to refer to the sexual orientation of a certain person, but for them, it is something that everyone experiences at one point in their lives, so they don&#8217;t know what it is.</p>
<p> In fact, when you look at it in a different light, our sex life is also &#8220;abnormal.</p>

<figure id="attachment_459654" aria-describedby="caption-attachment-459654" style="width: 894px" class="wp-caption alignnone"><a href="#" data-ident_hash="9917e1bf"><img src="https://res.cloudinary.com/fridaydigital/image/private/t_article_image/wpmedia/2026/03/7790cccdcaee4bdf3623a066d024b341.jpg" alt=""></a><figcaption id="caption-attachment-459654" class="wp-caption-text"> Evolution as an organism, diversity born of culture&#8230;two perspectives on sex</figcaption></figure>
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<p><a href="https://amzn.to/4cplJNI"> The Anthropologist&#8217;s Lesson on Sex&#8221; (Katsumi Okuno, Hayakawa Shinsho)</a></p>
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 Why are human sexes so diverse, unlike those of many animals that have sex only for reproduction? Anthropologist Katsumi Okuno reveals the reasons from two perspectives: biological evolution and comparative culture.

LGBTQ&#8221;, &#8220;fetishes&#8221;, etc&#8230; Is the over-diverse nature of human sex &#8220;the result of evolution&#8221;? What is &#8220;Sexual Anthropology&#8221;?

LGBTQ”, “fetishes”, etc… Is the over-diverse nature of human sex “the result of evolution”? What is “Sexual Anthropology”?

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