Wednesday, March 17, 2021

Lesley Newson and Peter Richerson's "A Story of Us"

Lesley Newson is Research Associate at the University of California, Davis. Peter Richerson is Distinguished Professor Emeritus in the Department of Environmental Science and Policy at the University of California, Davis.

They applied the “Page 99 Test” to their new book, A Story of Us: A New Look at Human Evolution, and reported the following:
A person who opens our book at page 99 will find three and a half paragraphs about marriage and sex! The text is however, hardly titillating. We are biologists and look at the role marriage and sex played in human evolution. Every human alive today is part of a lineage. We exist because our ancestors produced offspring that survived to produce offspring themselves. Marriage makes the survival of offspring more likely. It’s a “social tool” that binds families together and helps to ensure that babies will have the support of a father’s family as well as its mother’s family.

On page 99 we summarize the evidence that leads us to believe that the culture of our ancestors who lived in Africa 100,000 years ago already included the custom of marriage. One reason is the near ubiquity of marriage customs in the cultures of humans living today.

Another reason we give is that the human body is adapted to a life of restricted sexual relationships. Compared to our closest living ape relatives (chimpanzees and bonobos) human males have quite small testicles and they make weak underpowered sperm. This suggests that, during our recent evolutionary history, sperm from different men didn’t have to race up the uterus and fallopian tubes to fertilize an egg. Human sperm are joggers, not runners, probably because restricted mating customs gave them an open field. Our immune system is also poorly adapted to unrestricted mating. We are very vulnerable to sexually transmitted diseases. Some of the people who lived 100,000 years ago might have mated in an unrestricted way, but they are less likely to have been our ancestors. The support network for their babies would have been less secure and they would have been more at risk of being made sick or infertile by sexually transmitted bacteria and viruses.

Page 99 gives readers some idea of the nature of our book. It’s a book that aims to help readers understand themselves by describing their ancestors and the lives they lived, based on research from a wide range of disciplines. The ancestors described on page 99 had a much simpler culture than any humans living today but they were very similar physically and genetically.

In the case of our book, however, the usefulness of the page 99 test is limited. Our book isn’t just about our ancestors who lived 100,000 years ago. It begins with our ape ancestors who lived seven million years ago and finishes with the present day.

But a more important limitation is that page 99 reveals only one of the three styles of writing that make up the text of our book. Chapters 2 through 8 each contain a story (a science fiction story about the past) that illustrates what we think a life might have been like for one of our ancestors born during the featured time. Afterwards we summarize the evidence we drew on to write the story. Other pages (e.g., page 91) are partly fiction and partly evidence summary but page 99 is made up entirely of text that summarizes evidence. These evidence summaries don’t talk much about specific research, but they are linked to notes at the back of the book which contain the third style of text. The notes give more details and/or recommend further reading.

(We have written the book in this “multilevel” way because we think that a story of our origins should be for everyone, not just people trained in science.)
Learn more about A Story of Us at the Oxford University Press website.

--Marshal Zeringue