Sex at Dawn, part 1

Sex at Dawn: The Prehistoric Origins of Modern Sexuality is a popular science book, aiming to address that many of the common conceptions of human sexuality are incorrect.

Part 1 is 4 chapters long.

Chapter 1: Remember the Yucatan.

This chapter is basically an extended way of saying that culture defines a lot of what you consider normal. As such, it is important to recognize that just because something seems (un)natural doesn't mean that it is, and just because something appears to answer a question doesn't mean that it does.

This is a perfectly reasonable point, and I have no objections to it.

Chapter 2: What Darwin Didn't Know About Sex.

This chapter makes a few general points, though I feel it provides virtually no evidence to back up any of its arguments. There seems to be an implication that evidence in support of these claims will be presented later, but until I finish the book I won't know that for certain.

Central Argument: Assumptions about male sexual aggressiveness and female sexual passivity are wrapped up in the culture of Victorian England, in part because this was the context of Charles Darwin.

Darwin's straight-laced nature in regards to the erotic is discussed at length. So are the contributions of several other thinkers to Darwin's notions; particularly, Thomas Hobbes and Thomas Malthus. Hobbes wrote of "nature, red in tooth and claw", and that the in the natural state human lives were "solitary, poor, nasty, brutish, and short", all of which the authors contend are wrong, but they provide no evidence at this point that any of those statements are incorrect. They also discuss Malthus' argument that populations increase geometrically -- that is, doubling across generations -- while food production increases arithmetically (ie linearly) and thus poverty is intrinsic to nature as an important context for Darwin's thoughts on evolution, but the authors argue that this argument is based on incorrect assumptions about prehistory. At this point in the book, though, they do not state what these incorrect assumptions are.

The authors seek to lay out what they view as the standard argument of sexual selection: sperm are cheap, eggs and child care are expensive, men wish to maximize the number of women they can sexually monopolize, women wish to get investment in their children from one mate while potentially seeking out better genes when they're ovulating, men are sexually aggressive and fear sexual infidelity in women, women are coy and fear emotional/financial infidelity in men. They state that nearly all parts of this story are wrong, but they don't state how, or how they know this.

The authors also make frequent appeals to the idea that hunter-gatherer groups, and thus ancestral humans, were aggressively egalitarian and shared nearly everything, and that this should also be seen to include sexual relationships. This may be correct; I do not know. But I have some problems with the sorts of arguments being used:

1) The fact that some behavior is frequently reported in particular types of groups does not mean that it is actually common within these groups.

Humans lie. We do so for a variety of reasons. Possible examples include: our memories are inaccurate; our actions don't correlate perfectly with our ideals; we find it entertaining to see what we can get others (particularly strangers) to believe about us; the lie is seen as more interesting than the truth. I've seen all of these things happen, and on matters less intimate and taboo than sex. This is one of the reasons I value observation significantly more than self-reporting.

2) Current groups are not the same as our ancestors. As we frequently explain in evolutionary biology, humans didn't evolve from chimpanzees. Rather, humans and chimpanzees both evolved from a common ancestral species. It is unfortunately common for us to refer to "higher" and "lower" organisms, or describe some modern organisms as "primitive", but I think that that can lead to real confusion. There were creatures that looked similar to current turtles 220 million years ago (see Greg Mayer's easy to read account about a 2006 paper on a likely precursor to turtles 260 million years ago), but that doesn't mean that turtles haven't been changing for those 220 million years. Instead, it means that the parts which fossilize look quite similar. Behavior, soft body parts, enzymes, gene regulation, etc. can all change while leaving few fossilized cues. Body parts can also change significantly over time without being reflected as different within the fossil record, particularly if the changes are cyclic -- A gives rise to B which gives rise to C which gives rise to A.

The same applies to human societies. Modern hunter-gatherer groups are not necessarily indicative of what ancestral hunter-gatherer groups were like. They too have been adapting over the past 10,000 years in which agriculture swept the globe. Modern groups could easily be a non-representative sample of ancestral ones. Perhaps the groups which were most successful at the hunter-gatherer lifestyle have been the most likely to retain it, while those who were less successful at it switched to either agriculture or pastoralism. Perhaps hunter-gatherers were forced off of highly arable lands by agricultural groups who were more invested in it, and thus the remaining hunter-gatherer groups have needed to rely more on hunting than ancestral groups would have.

Chapter 3: A Closer Look at the Standard Narrative of Human Sexual Evolution.

This chapter goes somewhat more into depth on what the authors view as the standard narrative in human sexuality. Namely, they suggest that there are 4 basic assumptions:
1) Female libido is relatively weaker than male libido.
2) Male parental investment is relatively high in humans compared to many other species
3) Sexual jealousy is different between the sexes
4) Human females have extended sexual receptivity and concealed ovulation

From my understanding, all 4 of these assumptions are borne out by the data on humans. I could be wrong, but I don't yet have any reason to doubt these assumptions. The authors don't actually directly challenge any of these assumptions in this chapter, and they do mention studies which appear to support them -- such as that when women are ovulating they are more likely to wear perfume and/or jewelry, rate stereotypically macho appearance in men as more attractive, and seek out sex outside of a socially-recognized pair bond than they are at other points in their menstrual cycle. Perhaps in a later chapter they will present evidence contrary to one of these assumptions.

Instead, the authors largely cast aspersions on these assumptions by inflammatory language, such as that if women seek out mates based on their wealth, power, status, or protection, and men seek out mates based on their youth, and physical attractiveness, "Darwin says your mother's a whore." (p 50). I do not find that a useful approach in science. This comes closer to an ad hominem attack than a scientific argument, and logical fallacies are rarely good at establishing a point.

They also make faulty assumptions about absolute requirements on these notions, rather than relative requirements. For example, they note that it is questionable to assume that "In the ancestral environment, a man could know which children were biologically his, which presumes that: he understands that one sex act can lead to a child, and he has 100 percent certainty of his partner's fidelity." (p 54). While it would indeed be questionable to assume these things, they aren't necessary for the argument of relative male parental investment in humans. Evolution of behavior does not require conscious awareness of the roots of or the consequences of a behavior; it requires that the behavior be at least partially heritable and that individuals who engage in the behavior have, on average, more offspring than individuals who do not. There essentially isn't a morally-acceptable way for any individual to ensure exclusive sexual fidelity in a partner, but that's not required. Instead, if there are behaviors a man engages in which reduce the likelihood that he is raising offspring which are not genetically related to him -- and if raising offspring which are not genetically related to him reduces either the quality or quantity of his own genetic offspring -- then those behaviors are expected to be selected for, regardless of whether the individual man is conscious of the genetic effects of those behaviors.

None of this is to say that I think we should always model our behavior on what maximizes our own evolutionary interests. Adoption within humans is a good thing; children are not left to starve if their genetic parents die, and are sometimes removed from abusive/neglectful environments when the conditions are realized, and instead placed with adoptive parents. From my last reading of the relevant literature, adoptive parents are actually statistically better parents than are genetic parents, most likely due to the twin facts that a) they become parents by active choice rather than as a consequence of sex, and b) they typically must demonstrate capability of being parents in order to become adoptive parents. From an evolutionary angle, adoptive parents are likely passing on fewer copies of their own genes than if they focused on producing and rearing genetic offspring. That doesn't mean that they aren't making the right choice in becoming adoptive parents. One of the advantages of consciousness is the ability to make choices which may be contrary to our genetic predispositions.

Chapter 4: The Ape in the Mirror.

This chapter largely places humans within the context of the other apes, helpfully making the point that we are, indeed, apes (something often overlooked in humanity).

First there is a nice drawing of a phylogenetic tree of old world primates, and a verbal description of what it means. According to the book,

"If you picture relative genetic distance from humans geographically, with a mile representing 100,000 years since we last shared a common ancestor, it might look something like this:

Homo sapiens sapiens: New York, New York Chimps and bonobos are practically neighbors, living withing 30 miles of each other in Bridgeport, Connecticut and Yorktown Heights, New York. Both just fifty miles from New York, they are well within commuting distance of humanity.
Gorilla are enjoying cheese-steaks in Philadelphia, Pennsylvania.
Orangutans are in Baltimore, Maryland, doing whatever it is people do in Baltimore.
Gibbons are busily legislating monogamy in Washington, D.C.
Old-world monkeys (baboons, macaques) are down around Roanoke, Virginia." (p 62-63)

This is a nice picture. It's also very misleading. It is technically true because of the specific wording "relative genetic distance from humans". But I find this sort of description of a phylogenetic tree misleading because it gives the impression that, for example, gibbons are closer to orangutans than either are to humans. They're not. The last common ancestor between gibbons on the one hand (and realize that there are multiple species of gibbons), and the great apes (that include both orangutans and humans) on the other lived somewhere around 22 million years ago. The last common ancestor between orangutans and humans, on the other hand, was somewhere around 16 million years ago. That means that the genetic distance between humans and orangutans is somewhere around 32 million years -- 16 million along the path from humans to that ancestor, and 16 million along the path from the ancestor to orangutans. The genetic distance between humans and gibbons is about 44 million years. So far, so good. But the genetic distance between orangutans and gibbons is also 44 million years. This sort of geographic picture of distances only works relative to humans -- the distance between other groups is not preserved, and can easily be warped by the choice of where to place them.

The Machiavellian nature of meat sharing among the chimps at Gombe is discussed, and contrasted with the more egalitarian sharing by chimps at Tai. And it is noted that food shortage and surplus in humans tend to bring out heightened hierarchy within social organizations and greater Machiavellian and violent tendencies. But the authors simply assert, without evidence cited, that most of human prehistory had no food surplus to wn or lose and no home base to defend. I would like to see evidence of this before taking this assertion as true.

The authors take issue with the fact that much of the work about non-human primates stresses aggression. For example, they quote McGrew and Feistner with "Chimpanzees give a special call that alerts others at a distance to the presence of food. As such, this is food sharing of sorts, but it need not be interpreted as charitable. A caller faced with more than enough food will lose nothing by sharing it and may benefit later when another chimpanzee reciprocates." This is a very standard explanation of what is known in behavior/evolutionary biology as reciprocal altruism -- when the cost to an altruist is lower, and the benefit to a recipient is high, individuals may engage in behavior that is slightly costly to the them with the expectation that they will benefit when someone else does so in the future. The authors here take exception to why it is necessary to explain away generosity in nonhumans, instead of simply taking it at face value. My response is that altruism is less commonly observed in nature than selfish behavior is, and thus it is cases of altruism which must be explained.

One scientific fact that I find interesting which is brought up in this chapter is that both humans and bonobos, but not chimpanzees, have a repetitive microsatellite in a gene important in the release of oxytocin, a hormone which has many effects but is most known for its role in emotional bonding. They quote Eric Michael Johnson (original here, but you'll need to set your browser to not automatically redirect since he moved hosting shortly after that post went up) "It is far more parsimonious that chimpanzees lost this repetitive microsatellite than for both humans and bonobos to independently develop the same mutations." Maybe. I dug up the paper being referenced, and I can't conclude that from the original research. The sequences of this genetic region were compared in humans, chimps, and bonobos. There was no outgroup included, such as gorillas or orangutans. If other ape species do not share this repetitive microsatellite, either it appearing in the ancestor of humans-bonobos-chimps and being lost in the branch leading to chimps, or it being independently gained in both the branches leading to humans and to chimps requires 2 fixations on the phylogenetic tree. Further, this is a microsatellite repeat, which are among the most frequent classes of mutations, so the general argument that a gain of a specific mutation is less likely than the loss of it doesn't carry the same weight as it does with other types of mutations.

Thus far, I am not particularly impressed with this book. 78 pages into it, and the conclusion of what the authors label part 1, the book offers very little in the way of evidence. It is long on argument, but short on data, and either commits or comes close to several logical fallacies. Perhaps this section is meant primarily as background of what others have argued in the past, and other sections will provide data to bolster the claims made by these authors.