How Women Got Their Curves and Other Just-So Stories: Evolutionary Enigmas - David P. Barash, Judith Eve Lipton Curves garners a solid 3 stars for content – the subject matter is a fascinating look at a number of enigmatic characteristics of the human female. Unfortunately, the authors’ execution is so off-putting that I found it difficult to focus on the stories they told. Barash and Lipton write in a faux folksy manner that quickly grated on my mental ear. Little asides like this “…thus, it is a connection that even Stone Age men (and we do mean men) were able to make” and weak attempts at humor added up to an often excruciating reading experience.

For me, at any rate. Others might find it charming or not register it at all. Thus, I will recommend this book to anyone interested in human biology and evolution.

The authors’ purpose is not to champion any particular hypothesis about female biology but to examine various proposals that explain things like menopause and hidden ovulation, their strengths and their weaknesses. The areas covered are: menstruation, ovulation, breasts, orgasms, and menopause. In each area, human females prove to be unique or nearly so compared with their many mammalian relatives. Take menstruation, the subject of the first chapter devoted to female physiology – “Why Menstruate?” Why, indeed. Few mammals do it, and women far exceed other females in the amount of blood loss and the amount of tissue lost, and there’s an enormous energy cost paid to constantly rebuild the endometrium.

One of the nicer features of the book is that each chapter helpfully lists the hypotheses covered. In the case of menstruation, Barash and Lipton identify 16 possible reasons. While some, it turns out, are not likely, none command enough support to be entirely ruled out (p. 30):

1. An artifact of modernity
2. Signals the absence of pregnancy
3. Signals other women
4. Signals relatives
5. Signals to men that a woman is mature
6. Signals to men that a woman is not receptive to sex
7. Combats pathogens
8. Metabolic efficiency
9. Terminal differentiation
10. Evaluates the survivability of the embryo
11. Predator overloading
12. Encourages monogamy
13. Result of female-female competition
14. Social bonding
15. Social facilitation
16. Synchrony (of menstrual cycles) doesn’t exist

The book makes the point that, for whatever reason (and there’s a whole literature on why “female” issues are ill served in scientific research), menstruation and the other mysteries explored here remain enigmas because there’re so little data to evaluate, and what little there are can be interpreted in any number of ways. As the existence of so many theories demonstrates.

Ovulation, the next chapter, is another mystery poorly understood by science. Almost alone among mammals, women don’t make their fertility known in any overt way. Chimpanzee females, for example, proclaim their receptivity with red, swollen buttocks. Other species exhibit behaviors and/or emit scents that apprise a male that his amorous attentions are welcome. Human females don’t. At least not obviously. Some research suggests that subtle cues in changed behaviors and perceptions during ovulation may have some effect on male physiology but there’s no evidence of strong or overwhelming effects (p. 63f.).

In this chapter, 11 hypotheses are looked at with the same conclusion as in the previous chapter, i.e., some ideas are unlikely but none occupy such a strong position as to be definitive. In fact, it’s quite likely that several may be factors in the complex interactions that determine evolutionary success (p. 76).

The ideas (p. 62):
1. Not really concealed, just really, really inconspicuous
2. Provides sexual satisfaction (for the male)
3. Keeps the male guessing
4. Infanticide insurance – confuses paternity
5. Choose sire
6. Obtain resources (from males)
7. Minimize chaos
8. Competition avoidance
9. Lioness strategy (exhaust the male)
10. Facilitates infidelity
11. Consciously avoid pregnancy

Chapter 4 brings us to the breast (which also brings out some of the more obnoxious folksy writing). It will come as no surprise at this point to learn that human breasts are anomalous. Women are the only mammals who retain large and obvious breasts even when nonlactating. And again the question is what possible reason could Nature have had for selecting for this characteristic. Barash and Lipton identify only 15 possibilities (p. 97): Mimicking the buttocks, flotation devices, calorie storage (either as a pantry or to signal fitness), deception, provisioning, engineering (counterweights to the protruding butt), a variety of signaling strategies (releasers, symmetry, nubility, to other women), selection for desirable daughters, selection for a handicap, or vying for paternal investment (similar to the peacock’s investment in his tail or a stag’s in his horns).

Two are immediately dismissed as absurd – mimicking the buttocks to promote ventral (face-to-face) mating and flotation devices (related to the discredited idea that humans spent some part of their evolutionary history as aquatic mammals). The remaining all have points in their favor so the evolutionary biologist remains at a loss to explain the breast’s origin and function.

Then there’s the orgasm. Why a woman should be (potentially, at least) capable of one is another mystery. That it’s a nonadaptive artifact is unlikely for much the same reason menstruation isn’t – too much is invested in it. One of the more interesting facts I learned is that the clitoris has twice as many nerve endings as the penis, thus twice as sensitive (roughly speaking) (p. 127). As the authors note: “…female orgasm is complex, highly elaborated and downright technicolor compared to its comparatively feeble male counterpart. Rather than existing as an insignificant, pale imitation of where the genuine action is supposed to be (in men), female orgasm shows every sign of having been structured and fine-tuned by evolution” (pp. 126-27).

Here are the possibilities (p. 131):
1. Facilitates fertilization
2. Predator avoidance – post-coital quiescence
3. Positive reinforcement for sex
4. By-product of the male orgasm
5. Infanticide insurance
6. Pair-bond enhancement
7. Facilitates fertilization by creating a negative pressure that draws sperm into uterus
8. Reduces sperm flowback
9. Biochemical benefits
10. Sire choice
11. Determines social and/or genetic quality
12. Determines parental potential

The books final chapter tackles menopause and the abnormally long (compared to other mammals) post-reproductive lifespan. An interesting fact from this chapter: Greater survival rates of daughters and granddaughters when their grandmothers (particularly maternal granddams) live on (this is called “inclusive fitness”).

The current thinking about menopause includes the following hypotheses (p. 167): It’s an artifact of modern extended lifespans (not likely); it’s nonadaptive (just the expression of the ovaries exhausting their egg supply – again, not likely); it’s the by-product of an increased male lifespan; it’s a form of self-preservation; it’s a form of alloparenting and/or inclusive fitness; it’s a form of competition avoidance (giving way to the next generation); it’s various expressions of female longevity – backup chromosomes, sexual selection on males, “grandmothering” (see the “interesting fact” above).

As with all the other enigmas examined in this book, menopause results from the complex interaction of several factors (including some that may not be recognized yet). We just haven’t figured things out yet.

To reiterate, there’s a lot of interesting information in this book. I would recommend it to readers interested in human evolution or just in why (if they’re female) their bodies do the things they do or (if they’re male) why their partners act the way they act. I just wish it hadn’t been so “painful” to acquire it.