Why sex matters

By Bobbi S. Low.

Here’s what I wrote in my goodreads review:

“This book isn’t written by someone who read a few books and then decided to publish her own work on the subject – the book has 56 pages of references.

It’s a very solid piece of work with a lot of interesting stuff. A lot of work went into writing this book, and you can tell. Recommended.”

Razib Khan gave it 5 stars. So did I. Not all chapters are equally great and in general I’d say that I liked the first half of the book better than the second half. But I really couldn’t justify giving it any other rating.

I read the first couple of chapters while I was finishing the Adipose Tissue and cancer book – although this is a university press publication (published by Princeton University Press) it’s still a much easier read than the Springer publication, so I read it while taking breaks from the textbook. I should note that I read most of the book today and so it doesn’t actually take that long to read. Though I didn’t actually do a lot of other stuff today…

I was considering the problem of how to blog this book early on, and I decided to limit my coverage of it somewhat as I’d otherwise have to spend a lot of time on it; there’s a lot of good stuff in there and book-blogging takes time which I can’t spend reading (or, you know, doing other stuff). Some of this stuff was review and there are topics covered here which I’ve read about in a lot more detail elsewhere (e.g. stuff covered in Miller, or Dawkins), but the book also had a lot of new stuff. A nice thing about the book is that Low actually provides the data and the evidence for a lot of things which you’ve perhaps sort of assumed to be true but didn’t actually have great reasons for believing were true. Another nice thing is that she asks some questions you’d probably never thought about asking, and she also provides some interesting answers along the way. There are a lot of interesting observations in there.

I should note that in (/quite?) a few chapters she covers work done by Robert Boyd and Peter Richerson. I’ve known for a while that I ought to have a go at some of their stuff, and I actually recently purchased The Origin and Evolution of Cultures – but at this point I’ve skimmed parts of it, and that book just looks like a lot of hard work, so I’ve sort of shied away from it so far.. I think Low convinced me that I really ought to have a look at that stuff ‘at some point’ when I feel up to it.

I have added some hopefully illustrative quotes from the book below:

She gives a breakdown of what the book is about in the introduction:

“I will begin with the basic arguments and assumptions of behavioral and evolutionary ecology: selfish genes, conflicts of interest, and why two (and not more or fewer) sexes have specialized to reproduce through different behaviors (chapters 1–3). Then I ask: How do these basic sex differences, whose theory we understand, actually play out in other primates, as well as humans (chapters 4–6)? Next, I take an empirical glance at the diverse ways in which both traditional and transitional societies make a living, how men’s and women’s roles and lives diverge, and how even marriage is affected by ecology and resources (chapters 7, 8). The complexity of these patterns leads us back to basic theory to explore how conflicts of interest are mediated, literally from the level of genes in genomes to whole societies (chapters 9, 10). Sex differences and conflicts of interest help us predict why there are so few women warriors or high-roller politicians in most societies—and the kinds of societies in which they are likely to occur (chapters 11–14). And finally I ask: How does our evolutionary past interact with current global population and resource consumption problems (chapter 15)?”

Some other quotes:

“many people may be appalled at the approach I will use here, that is, to assume that we humans are as predictable as other animals in our behavior, and are governed by the same rules. And I want to begin with simple rules, no less. Many of us assume that humans operate under rules that are different from those of other species, that our rules are culturally based rather than biological. I will ask: What can we learn if we begin without assuming that this were true? […] My explorations here assume that humans are indeed animals, even if elegantly complex ones, and that they are therefore subject without special exemption to the general rules of natural selection, the rules that govern behavior and life history among living things. […] In their “deep” objectives—in what they evolved to do—humans are not qualitatively different from other living organisms. Like other living things, they evolved to get and use resources to survive and enhance the spread of their genes.”

“When societies lack rules of inheritance, suggesting that there is little to inherit, men typically do not exchange goods for women, but exchange women;37 when there are no societal rules about wealth or hereditary class stratification, men are similarly more likely to exchange women than goods. But even in such societies, resources are not irrelevant to the pattern of exchange. […] when men purchase wives (bridewealth societies), younger (higher reproductive value) women are worth a higher bride price.38 The currency of choice varies: sometimes women are purchased with cattle, as among the Kanuri people; sometimes with sheep, as among the Yomut Turkmen; sometimes with pigs, as among the Tsembaga-Maring; or a combination.” [Some more details are given later in the book and I couldn’t help myself from quoting this part:] “the Turkmen are a bridewealth society, and bridewealth is high. A man of median wealth will pay two to four years’ income for a virgin bride. In concrete terms, this is ten camels for the bride’s father and one camel for her mother, or the bridewealth can be paid in cash or other livestock. One camel equals two horses, one really good race horse, two cows, ten sheep, or ten goats.”

“We can break preferences down into signals that reflect health (shiny hair, clear skin) or youth (no wrinkles or sags) and current reproductive stage (waist-hip ratio, color of nipples); signals that suggest other reproductively important attributes like wealth; signals that reflect social awareness (stylishness, which may be purely culturally defined); signals of belonging to a certain group. Cross-culturally among traditional societies, the things people describe as attractive in the other sex turns up all of these categories. […] selectively relevant traits consistently rank high. […] Certainly cultural and historical factors strongly influence these preferences, but some preferences—healthy, young, not pregnant— are virtually universal. […] Put simply, in our evolutionary history, it seems likely that a woman’s value was usually her reproductive value, and a man’s value was his resource value.”

“in most societies, the reproductive interests of more than the two who mate can matter. In traditional societies, the potential bride had greater say than the would-be groom in marriage negotiations in only 3.7 percent (3/81) of societies.27 Grooms had greater— or sole—say in 39.5 percent (32/81). In most of these societies, the older generation had considerable power in these decisions.” [the source given is ‘Whyte, 1978, 1979’ – I feel reasonably certain the data used is from the Standard cross-cultural sample, an oft-used resource in this book.]

“Typically, perhaps sentimentally, we view pregnancy as a time of maternal support and care for the growing embryo. But genetic conflicts over resources start here. An infant in utero is only half like its mother […] Thus the stage is set for conflict, both with mother and any siblings who share the womb […] Fetal genes from Dad that increase Mom’s transfer of nutrients to the fetus will be favored. Will such a transfer harm Mom? No matter, so long as she is healthy enough to continue investing, from the fetus’s point of view. In fact, if her ability to produce other (competing) siblings is reduced, so much the better. […] As early as the implantation of the zygote on the uterine wall, trophoblast cells (fetally derived) invade the lining of the mother’s womb and remodel certain arteries so that they cannot constrict to shut down blood flow to the fetus. This means several things. A mother cannot control the blood or nutrient flow to the fetus without affecting herself as well, and the placenta can now release hormones directly into the mother’s blood stream. Some of these manipulations are countered by maternal strategies. Fetus and mother are truly combatants in an arms race. As biologist David Haig has cogently pointed out, a number of unpleasant accompaniments of pregnancy (as well as serious medical conditions like preclampsia) are better explained as maternal-fetal conflict than by any competing theories.”

“The importance of resource value for men versus reproductive value for women means that in many societies it may be harder for a man to get a wife than for a woman to get a husband […] If the reproduction of sons is more variable than that of daughters, and especially if wealth or status matters more to men’s success than women’s, investment is likely to be biased toward sons. […] when parental investment can influence the reproductive success of one sex more than the other (as in baboons), there should be a correlation between parental condition and investment in that sex.”

“in Locknevi parish [Sweden] during the period of this study [1824-1896], resources shifted from being relatively uneven with some very large holdings, to being more even but limited. […] Locknevi folk married early but delayed having children. A man’s best occupation influenced his chances of marrying: 74 percent of agricultural workers and servants living their entire life in the parish failed to marry, compared to 20 percent of lower-middle-class men. […] Sixty-one percent of women failed to marry while in the parish […]

The quote above, and a few others in that chapter, basically made me aware that I have had some questionable ideas about how this part of human history was like for most people. I have sort of implicitly assumed that most people in this historical period had relatively few problems getting married, even those in the ‘poor peasants’ segment [and do remember that there were a lot of poor peasants in the past] – but the data presented in this chapter, including also data from three other areas of Sweden during this period, tells a quite different story. And this is good data, as good as it gets. In Nedertorneå, another Swedish parish, almost two-thirds of all women who didn’t leave the parish didn’t get married: “Sixty-four percent of women failed to marry while in the parish”. Incidentally, in some places resources mattered a great deal; here’s what things were like in the Tuna parish:

“Landowners [men] were almost certain to marry (95 percent), in stark contrast to other men (35 percent); they married women about 2.5 years younger than other men, and had about one to 1.5 more children.”

Such effects were not always present, but as Low remarks in the chapter, “whenever wealth or resource differentials existed, resources and reproductive success were positively correlated.” And differences across social groups, even in an ethnically homogenous country like Sweden, were huge and persistent back then – here’s another observation:

“Of men who stayed in their birth parish, poor [occupational status of cottar – tenant farmers – or proletariat and no land ownership record, US] sons of poor fathers were most likely to remain unmarried (57 percent); 97 percent of such poor, unmarried men had fewer children than other men. Rich [owned land and/or had an occupational status of upper middle class, lower middle class, or bönder [farmer], US] sons of rich fathers had an approximately equal chance of marrying or not (48 percent versus 52 percent), and once married had a 59 percent chance of having relatively large families. Rich sons of rich fathers who did not marry were, like poor sons of poor fathers, likely to have fewer than the median number of children. Although 97 percent of poor sons had this fate, only 55 percent of rich sons did.”

As I mentioned, there’s a lot of interesting stuff in this book.

October 7, 2013 - Posted by | Anthropology, Biology, Books, Demographics, Ecology, Evolutionary biology, History

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