Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live by Marlene Zuk Read Free Book Online Page B

mentioned already, they seem to be undergoing such an image transformation that the usage was apparently irresistible. The supposedly salacious news comes from another examination of fossil fragments, finger bones this time, taken from Neandertals, four species of ancient hominoids, some early but anatomically modern humans, and data from four kinds of modern apes, including gibbons. The authors, led by Emma Nelson of the University of Liverpool, were interested in the kind of mating system our ancestors and their relatives might have had. 34 Did males compete with each other to gain access to multiple females, or were the species monogamous? Overall difference between male and female body size is often an indicator of the degree of multiple sex partners in a species, since selection for more competitive males often means that those males are heftier and hence better fighters. The more extreme the difference between the sexes, the more exaggerated the mating system. Male elephant seals, for example, are two to three times the size of females, and mating success in this species can be extraordinarily skewed, with a single bull in one population siring over 90 percent of the pups and the majority of the losers having no offspring at all.
    Gauging overall body size difference between males and females can be tricky, however, if all you have are a few skeletal bones from each sex. What if you happened to measure an exceptionally large female or exceptionally small male? The finger bones were used because the ratio between the index (second) finger and the ring (fourth) finger is believed to reflect the levels of male sex hormones that an individual was exposed to while in the womb. In men, the second digit tends to be shorter than the fourth; in women, either the two fingers are more or less the same size or the second is slightly longer than the fourth. Lower ratios thus could indicate higher levels of male sex hormones, which might be expected in a species with greater male competition and less long-term pair-bonding.
    Over the last decade or so, this ratio between the lengths of the digits has attracted attention from evolutionary psychologists, who purportedly found that sexual orientation, musical ability, female fertility, and several other characteristics were reflected in differences in the finger ratios of the subjects. 35 Nelson and her colleagues went a step further: instead of looking at the ratios within a population, they compared digit ratios among all of their specimens. We already know that gorillas, chimpanzees, and orangutans have multiple sex partners in a breeding season, whereas gibbons are relatively monogamous. Of the fossil species, all but Australopithecus afarensis —Lucy’s species—had digit ratios suggesting that they were more like the gorillas or chimps and less like the gibbons, and the Neandertals were considerably more like those somewhat promiscuous species than are modern humans. Hence, presumably, the headlines about Neandertal “randiness,” as the UK Mirror put it. 36
    Can we conclude, then, that the majority of our ancestors and their relatives, including the Neandertals, had a mating system in which men were able to have multiple wives, and that our monogamy is therefore a recent innovation? Maybe not. 37 Nelson and her fellow researchers were quite cautious, noting that their sample of bones was tiny, and that if the results were corroborated by, say, additional data on body size differences between the sexes, “digit ratios represent a supplementary approach for elucidating the social systems of fossil hominins.” 38
    The use of digit ratios has been controversial almost from the start, with some researchers, including Luká š Kratochvíl and Jaroslav Flegr of the Czech Republic, suggesting that the difference is a statistical artifact arising from the simple fact that men have larger fingers than women. 39 We also know virtually nothing about how to interpret the numbers