Women in Evolution & Science: Running with the Boys

Women in Evolution

Animal breeders knew how to obtain lineages with desirable characteristics long before Charles Darwin formulated the theory of natural selection to explain how new species emerge from earlier ones. Taking a cue from animal husbandry, Darwin understood that the differences between current and future generations depend largely on which individuals reproduce, and which do not. At its most basic level, evolution is manifested in changed frequencies of characteristics as they are inherited from one generation to the next (microevolution). For example, if 50% of one generation has blue eyes, but only 40% of the next generation does, then microevolution has occurred. Depending on geographical circumstances and time, the cumulative effects of generation-to-generation changes may result in the emergence of new species (macroevolution). In both cases, evolution boils down to who lives and who dies.

Genetic studies reveal that our closest nonhuman cousins are the chimpanzees, and that we are a little more distantly related to the other great apes (gorillas and orangutans). Numerous scientific studies also show that our direct ancestors (hominins) split from those of chimpanzees around five to seven million years ago. Paleoanthropologists make educated guesses about what early hominins were like by studying the hominin fossil record, comparative anatomy, primate behavior, and the lifestyles of people living in non-industrialized societies. The best guess is that our earliest hominin relatives lived in social communities in which males did some hunting and scavenging for meat, while females focused more on gathering plant foods. Paternity would not have been understood, and mothers and nursing infants would have been inseparable. Small groups of females and juveniles probably foraged together during the day, and reunited with the larger community before settling in trees to sleep at dusk.

But how do we get from this very apelike picture of early hominins to the Homo sapiens that we know and love today? Certain clues help to answer this question. We know that our ancestors became adept at walking on two legs, developed increasingly large and complex brains, invented a variety of tools, became crafty (some would say sneaky) in their social realtionships, and originated language. Paleoanthropologists agree that all of these delopments profoundly influenced hominin evolution. Where they disagree, however, is on the identification of the sex that was chiefly responsible for the evolution of these advanced hominin traits.

The classic literature in anthropology has been extremely male-biased when it comes to designating the primary movers and shakers of human evolution. Thus, males are hypothesized to have invented tools and language in conjunction with hunting (and, some would add, warfare). According to this man-the-hunter hypothesis, big brains were selected in males in conjunction with these activities, and brain size in women increased only because they rode on the gentic coattails of their betters. More nuanced social communication, with stronger male-male bonds, is also included as part of the hypothetical masculine evolutionary package. Beginning in the 1970’s, it became widely acknowledged that foraging women in non-industrialized societies actually bring home most of the calories, which led to the woman-the-gatherer hypothesis. That hardly made a dent in the profession’s male bias, however. One researcher even suggests that walking upright was selected for in male hominins so that they could carry plant food that they (the men) had gathered to females, who were seen as too burdened with youngsters and too helpless to fend for themselves!

Inconvenient facts have not interfered with the man-the-hunter/gatherer/inventor hypothesis. For example, among higher primates documented to have invented new techniques or tools (great apes, Japanese macaques), it is usually (if not always) the females who do the initial inventing, and frequently juveniles who spread the inventions. Similarly, the relatively recent human invention of Nicaraguan Sign Language for the deaf was carried out by children. The origin of language was crucial for human evolution, and extensive scientific evidence from multiple disciplines suggests that women and children initiated the invention of language, as detailed in Finding Our Tongues: Mothers, Infants & the Origins of Language.

But the most inconvenient truth that is relevant to the roles of the sexes during hominin evolution goes back to the first paragraph in this section. In its essence, evolution depends on who lives and who dies. The qualities selected for in future generations are determined by the babies who survive, grow up, and have their own babies. Now go back to our apelike picture of early hominins, in which mothers and nursing infants are inseparable and spend their days foraging in the company of other females and youngsters. As is the case for living apes and humans in traditional societies, infant mortality would have been high. The hominin babies who charted the destiny of our species were the ones that lived. Somebody had to keep them alive, and that responsibility fell to their mothers. Early hominin women were, thus, the ones who facilitated the genetic legacy of Homo sapiens. In that sense, they were the mothers of us all.

Women in Science

As noted, evolution is about who lives and who dies, otherwise known as “differential mortality.” Some years ago, I wrote a tongue-in-cheek commentary about immortality in women scientists based on an analysis of death notices and obituaries in Science every ten years from 1949 until 1969 (after which it regularly stopped publishing these) and every ten years in Nature from 1949 to 1999. Although over a decade has passed since the commentary appeared, my perusal of the same two journals suggests that women scientists can continue to celebrate their differential immortality. For fun, the commentary is reproduced below.