Category: Blog


Published: June 4, 2013

Evolution of Human Reproduction

Robert Martin, Curator Emeritus, Negaunee Integrative Research Center


url for Blog in Psychology Today:

Book Description: Despite the widespread belief that natural is better when it comes to sex, pregnancy, and parenting, most of us have no idea what “natural” really means; the origins of our reproductive lives remain a mystery. Why are a quarter of a billion sperm cells needed to fertilize one egg? Are women really fertile for only a few days each month? How long should babies be breast-fed? In How We Do It, I draw on forty years of research to locate the roots of everything from our sex cells to the way we care for newborns. I examine the procreative history of humans as well as that of our primate kin to reveal what’s really natural when it comes to making and raising babies, and distinguish which behaviors we ought to continue—and which we should not. Although it’s not realistic to raise our children like our ancestors did, my investigation reveals surprising consequences of—and suggests ways to improve upon—the way we do things now. For instance, I explain why choosing a midwife rather than an obstetrician may have a greater impact than we think on our birthing experience, examine the advantages of breast-feeding for both mothers and babies, and suggest why babies may be ready for toilet training far earlier than is commonly practiced. How We Do It offers much-needed context for our reproductive and child-rearing practices, and shows that, once we understand our evolutionary past, we can consider what worked, what didn’t, and what it all means for the future of our species.

Robert Martin
Curator Emeritus, Negaunee Integrative Research Center

My book How We Do It: The Evolution and Future of Human Reproduction was released by Basic Books on June 11, 2013. In connection with the book, I recently started a regular monthly blog with Psychology Today.

In the tree of life, human evolution is a very unusual case in many ways. If the focus of study is too narrow, it is difficult to avoid special pleading. My long-term research strategy has hence been rooted in the conviction that a wide-ranging approach is essential to identify reliable general principles. Secure interpretation of our biological origins demands comprehensive study of primate evolution from its earliest beginnings. In this spirit, I have conducted sweeping comparisons across primates, covering anatomy of both living and fossil representatives, ecology, behaviour, reproduction and molecular evolution. Study of size relationships (allometric scaling) has been a pervasive theme. A synthetic approach to primate evolution has several benefits. In addition to generating sound general principles, it can reveal relationships that otherwise escape detection. One illustrative example is provided by the endeavour to determine times of divergence in the primate tree, notably the split between humans and chimpanzees. Because of major gaps in the fossil record, estimation of divergence times from earliest known fossil relatives can be seriously misleading. Statistical analysis of the numbers of living and fossil primates in combination with an evolutionary tree based on DNA evidence reveals that divergence times within the primate tree are generally substantially earlier than has often been claimed. In particular, the divergence between humans and chimpanzees  —  widely held to be around 5 million years ago  —  in fact appears to be closer to 8 million years ago. Another good example is provided by the close connection between brain size and reproductive biology. Only by examining these features in tandem was it possible to infer that maternal energy resources played a vital part in the evolution of the brain. The "Maternal Energy Hypothesis" is particularly relevant to interpreting the evolution of our own very large brain since we diverged from chimpanzees.