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I was recently reading a book published by some anonymous biologist known as Lynn Saxon, in which she appears to want to refute Christopher Ryan's thesis in Sex at Dawn that prior to the invent of agriculture, humans were presumably far more promiscuous and had sex not just for reproductive purposes.

In order to do this, she then goes on to show how, in the animal world, the great majority of all sexual activity is directed only towards reproduction. Another author, David Barash, says similar things: namely, that "evolution is very much about reproduction—variation in reproductive success is evolution".

However, homosexual behavior is anything but reproductive. Saxon appears to suggest indirectly that all such "non-reproductive" behaviors that are "useless from a evolutionary point of view" are rare and unnatural among primates, who are our closest relatives.

One more biologist, known as Antonio Pardo, says:

"Properly speaking, homosexuality does not exist among animals…. For reasons of survival, the reproductive instinct among animals is always directed towards an individual of the opposite sex. Therefore, an animal can never be homosexual as such."

Is this true? Is homosexuality really uncommon and unnatural among our closest relatives who are primates? Is sex mostly for reproduction?

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    $\begingroup$ If you feel like John answered, you can click on the checkmark next to his answer as to classify this question as "answered". $\endgroup$ – Remi.b Sep 16 '18 at 17:22
  • $\begingroup$ regarding sexuality previous to agriculture, tribal sexual practice and culture varies starkly and heterogeneously per tribe, some tribes are hyper sexual, homo, straight, cannibal, nonviolent, sadistic, spiritual, there is great variety in cultures, just see bhutan vs aztec, hawaiian vs european. ... In human history there is the book of the dead from Babylonian times, the epic of Gilgamesh, the 1001 nights, and the Greek cultural documents, which give a lot of information about early historical orgies and homosexuality. Generally, humans tribes are dominantly heterosexual. $\endgroup$ – com.prehensible Sep 21 '18 at 10:41
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First Antonio Pardo is not a biologist, he is a professor of bioethics and his degrees are in medicine and philosophy.

Second, Clearly he does not know anything about primates, since there is one famous great ape that has sex even more often than humans do, the Bonobo. Bonobo have sex for everything, hello, goodby, conflict resolution, social bonding, ect. Bonobo engage in homosexuality and a hundred other sexual practices, including some things humans can't do, like penis fencing. Bonobos along with chimps are also our closest living relative.

As for other animals there are hundreds of examples of homosexuality in nature. I hate using all these wiki links but this is such general biological knowledge I would need either dozens of links or a link to a textbook.

As for Lynn Saxon, first let me say she does not have a degree in anything, It is possible Lynn Saxon is not even her real name.

Now for her argument, it is true that in nature sex is most often directed towards reproduction (that is why it evolved in the first place* and just consider how many sexual animals have very simple behavior), but as I have pointed out there are notable exceptions one of them our closest relative. And not just homosexuality, masturbation is observed in nature as well. Also consider monogamy is also extremely rare in nature with the exception of birds, arguing humans should behave based on how other animals act will not help their argument. It is also a common fallacy, what is natural and what is ethical are not related, Sanitation, science, religion, medicine and reading are also not natural.

If you want to read more about humans and our relatives I suggest the book (the Third chimpanzee" by Jared Diamond as a t least a good starting book. "Wild Connection" by Jennifer L. Verdolin is even better, both have actual degrees in biology.

*Of course your legs originally evolved as fins, so what something starts as is not necessarily what it is used for now.

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  • $\begingroup$ "As for Lynn Saxon, first let me say she does not have a degree in anything, It is possible Lynn Saxon is not even her real name." How do you know that she doesn't have a degree in anything? And yes, OP said: "book published by some anonymous biologist known as Lynn Saxon", so yes, according to OP she is anonymous and it appears not to be her real name. As for Bonobos being homosexual. It depends on what you mean by homosexual precisely. See my answer that attempts to clarify this point. Other than, I agree with your answer, and I think the answer is good. $\endgroup$ – Eff Sep 17 '18 at 10:10
  • $\begingroup$ Because she hasn't claimed one, and may not have even be using her real name. Degrees and expertise are not something you get the benefit of the doubt on. $\endgroup$ – John Sep 17 '18 at 14:08
  • $\begingroup$ No, degrees are something you either have or you don't. I know many people who don't talk about their degrees despite having one. The fact that they don't mention their degrees doesn't mean they don't have one. $\endgroup$ – Eff Sep 17 '18 at 16:48
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    $\begingroup$ talk about is not the same as publish a book on the subject.Sure it is hypothetically possible she has a degree in something, but the default position and only reasonable way to consider her words has to be she does not unless she demonstrates otherwise. $\endgroup$ – John Sep 17 '18 at 17:23
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First, let me say that there are vast amounts of criticism toward the book Sex at Dawn by experts on the topic of the evolution of human sexuality, but generally for reasons other than homosexuality. See here. But that's not what you're really asking about.

I believe there is possibly some miscommunication going on here. Some of the statements in the question, I think, are true and makes sense. Some statements are not totally clear, and the answer depends on how exactly they are interpreted. Others are wrong. Let's see.

In order to do this, she then goes on to show how, in the animal world, the great majority of all sexual activity is directed only towards reproduction.

It is possible that this is true statistically. I'm not sure. However, there is certainly many examples of non-reproductive sexual behavior. See the Wikipedia article: Non-reproductive sexual behavior in animals. One obvious example is the Bonobo.

Another author, David Barash, says similar things: namely, that "evolution is very much about reproduction—variation in reproductive success is evolution".

This statement I think is far more reasonable. It is true, in the ultimate sense, that the main purpose of sex is reproduction. And behavior that increases the probability of reproduction is going to be selected for. (Technically, it would be more true to say that natural/sexual selection is about variation in reproductive success. Evolution contains more than selection, for example drift).

However, homosexual behavior can easily arise naturally in the animal kingdom, especially as a side-effect. One way this can happen is the following: feeling pleasure through sexual stimulation is adaptive, because this increases the probability that individuals engage in sexual behavior, which ultimately leads to more offspring. However, as a side-effect of sex being pleasureable, this means that animals may engage in sexual behavior that is non-reproductive (e.g. homosexuality or masturbation).

As long as non-reproductive sexual behavior is not done to the exclusion of reproductive sexual behavior, there is no reason to suspect that the non-reproductive sexual behavior negatively affects reproductive success (and hence, non-reproductive sexual behavior can perfectly well exist).

Despite the original ultimate reason for sexual behavior is to facilitate procreation, sexual behavior may even possibly become adaptive for reasons other than procreation. For example, it may start facilitating social bonding.

This naturally leads to the following problem, when looking at the following quote:

"Properly speaking, homosexuality does not exist among animals…. For reasons of survival, the reproductive instinct among animals is always directed towards an individual of the opposite sex. Therefore, an animal can never be homosexual as such."

When asking whether homosexuality is common in nature, we need to define precisely what we mean by homosexuality. If a human man says that they're homosexual, that can mean several things. It may be that they are attracted to mostly men, or both men and women, or only men. If they are attracted to only men, they are, what I would call, strictly homosexual. If given free choice they would in a majority of situations prefer to have sex with another man, I would call them primarily homosexual. In this sense, our Bonobo male friends are typically neither strictly homosexual or even primarily homosexual, because a male that engages in homosexual behavior is also willing to engage in heterosexual behavior. Strict homosexuality or primary homosexuality does appear to be quite rare in nature (although there are some examples known. For example, in rams a few percent seem to prefer same-sex even when given the choice). In the quote, when they say 'properly speaking' they may be talking about what I have denoted strict homosexuality. The quote is a bit hard to interpret. If they simply mean homosexual behavior, then no, that is not particularly rare.

Is this true? Is homosexuality really uncommon and unnatural among our closest relatives who are primates?

Strict or primary homosexuality is uncommon, homosexual behavior is fairly common (and therefore clearly not extremely unnatural).

Is sex mostly for reproduction?

In the ultimate sense, the original and most important purpose of sex is reproduction. But as I've detailed out, non-reproductive sex can still easily arise without it negatively affecting fitness. It may even possibly become adaptive (if it is not done to the exclusion of reproductive sexual behavior).

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  • $\begingroup$ I would hesitate to claim what the most common form homosexuality humans engage in without evidence. research shows such forms of homosexuality are actually very rare, tandfonline.com/doi/abs/10.1080/… and yougov.co.uk/news/2015/08/16/half-young-not-heterosexual $\endgroup$ – John Sep 17 '18 at 14:06
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    $\begingroup$ @John I think you misunderstand what I meant. Perhaps I didn't communicate myself properly. I am not saying that the most common non-heterosexual orientation is strict homosexuality. I am saying that when people say that they're homosexual, they tend to prefer only or mostly their own sex. Otherwise, they tend to use another term ("bisexual", "queer", etc). I completely agree that strict homosexuality is not the most common form of non-heterosexual orientation. $\endgroup$ – Eff Sep 17 '18 at 15:40
  • $\begingroup$ @John Nevertheless, it is also not important for my answer whether which type of homosexuality is the most common. My only reason for making the term 'strict homosexuality' is to make the answer more clear, and to adress the fact that some types of non-reproductive sexual behavior exists and are more common than other types. I have edited my answer to remove emphasis of which type is more common (because it is not necessary for my answer). $\endgroup$ – Eff Sep 17 '18 at 15:49
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    $\begingroup$ And again studies show otherwise people do not identify in those ways consistently or reliably, it is a bad assumption to make. Additionally strict homosexuality is mostly irrelevant since it is the quoted authors are not defining homosexuality that way. $\endgroup$ – John Sep 17 '18 at 16:26
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    $\begingroup$ @John No, what is irrelevant is how common strict homosexuality is. It still is worthy of clarification. If the authors don't define homosexuality that way, then even better that I clarify exactly what I mean with each term. You don't have to go to strict homosexuality, but just preferred sex. If a man in more than 50% of occasions will prefer to have sex with another man rather than a woman given free choice, you could call him 'primarily homosexual.' Primary homosexuality is also not common in the animal kingdom, although as I discussed there is some evidence for it (in rams, in particular). $\endgroup$ – Eff Sep 17 '18 at 16:45

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