Episode 85: David Geary discusses our shrinking brains, cognitive development  and sex differences

// Mar 26, 2019

Today’s guest is Dr. David Geary, a cognitive developmental scientist whose wide-ranging interests are particularly focused on evolutionary psychology, sex differences and children’s mathematical development.

He is a Curators’ Distinguished Professor and a Thomas Jefferson Fellow in the Department of Psychological Sciences and Interdisciplinary Neuroscience Program at the University of Missouri Columbia.

David’s book, “Male, Female: The Evolution of Human Sex Differences,” has been described as a landmark text that provides a comprehensive evolutionary model to explain sex differences. His research on children’s mathematical development resulted in a MERIT award from the National Institutes of Health. In addition to authoring four books, he has published more than 300 articles and chapters across a diverse range of topics.

David has served as a member of the President’s National Mathematics Advisory Panel and was appointed by President George W. Bush to the National Board of Directors for the Institute for Education Sciences.

Show notes:

[00:02:36] Dawn asks about David’s childhood, mentioning that his family moved around quite a bit before settling down in Northern California.

[00:03:00] Dawn asks if David’s early struggles in elementary school were due to jumping around from classroom to classroom because of family moves.

[00:03:43] David talks about how he first became interested in science.

[00:04:15] Ken asks why David decided to go to Santa Clara University in Silicon Valley.

[00:04:47] David explains how he ended up majoring in developmental psychology.

[00:05:18] David recounts the story of how he went from working at an auto parts store to getting his master’s degree in clinical child and school psychology at California State University.

[00:06:06] Dawn mentions that before David earned his master’s degree, he went to work as a school psychologist and counselor. She then asks what led him to decide to enter the Ph.D. program as the University of California Riverside.

[00:07:05] After finishing his Ph.D., David had a number of university positions before landing at the University of Missouri in Columbia. Ken asks David about the school’s interdisciplinary evolution group, which was a key reason David was interested in the university.

[00:08:12] Dawn asks how children’s mathematical development and evolutionary psychology became two of David’s primary research focuses.

[00:10:04] David summarizes the factors that determine human intelligence.

[00:11:11] David explains why the attempt to define intelligence has always been a controversial issue.

[00:11:51] Ken asks about David’s research in the ‘90s that made a distinction between evolved forms of cognition, such as language, and other forms of cognition that are more dependent on schooling, such as reading and arithmetic.

[00:14:44] David talks about his interest in Evolutionary Educational Psychology, and how that relates to the insights gleaned from his recent article that argued that there is built-in scaffolding that helps a child’s mind learn to talk, use tools, and play, but that there is nothing of the sort for learning how to read, write, or do math.

[00:17:14] David has been investigating children’s mathematical cognition for nearly 25 years, including a 2015 paper on the numerical foundations of young children’s mathematical development.Dawn asks David to share his key takeaways from this research.

[00:20:08] David gives an overview of the MU Math Study, which is supported by the National Institutes of Health and the National Science Foundation, and focuses on mathematical development from preschool all the way through high school.

[00:22:32] David discusses his research into human sex differences, and human sexual selection.

[00:23:46] Dawn asks about David’s paper that focused on human cognitive sex differences, which illustrated how sexual selection can result in sex differences in the brain and cognition. The paper also explored how these differences appear to be related to mitochondrial functioning, which led David propose a taxonomy of sex differences in human condition-dependent cognitive abilities. Dawn asks David to talk about these underlying brain systems and their development.

[00:26:36] Ken asks how disease, premature birth, and pre- and postnatal exposure to toxins affect males and females differently.

[00:28:56] Dawn mention’s David’s 2018 paper in “Psychological Review”that argued that the overall efficiency of mitochondrial functioning is critical to general health, brain development and functioning, as well as age-related changes in health and cognition. She goes on to ask David about his view that mitochondrial functioning provides a plausible basic biological mechanism that underlies the relations among all these phenomena.

[00:32:10] Ken mentions Doug Wallace, one of the pioneers of mitochondrial research, who was interviewed on episode 67 of STEM-Talk, who has shown that mitochondrial haplotypes have adapted to the environment, with some being better adapted to colder weather. He asks David if these haplotypes are at greater risk of decreased intelligence due to their decreased ATP efficiency as a result of their environmental adaptation.

[00:33:52] Some whole genome sequencing studies have suggested that several hundred genetic loci associated with intelligence might explain 5 to 10 percent of an individual’s intelligence. One interpretation of these results would suggest that the environment is by far the largest determinant of human intelligence. Dawn asks how these findings might be integrated into David’s mitochondrial hypothesis.

[00:37:04] Ken asks if the sexually-dimorphic differences in cellular antioxidant capacity translate to differences in mitochondrial function and intelligence over the lifespan.

[00:39:57] Dawn asks why mitochondrial approaches to treating neurological diseases have not resulted in improved outcomes.

[00:39:30] David talks about his interest in Evolutionary Educational Psychology, and how that relates to the insights gleaned from his recent article that argued there is built-in scaffoldingthat helps a child’s mind learn to talk, use tools, and play, but that there is nothing of the sort for learning how to read, write, or do math.

[00:42:21] Ken mentions that David, and a number of other scientists, were cited in a 2010 Discover magazine article titled, “If Modern Humans Are So Smart, Why Are Our Brains Shrinking?”Ken asks David to talk about why human brain volume is shrinking.

[00:44:28 Dawn asks if there is evidence to give credence to the idea that because more educated men and women are procreating later, or not at all, is contributing to our decreasing brain volume.

[00:47:02] Dawn asks about the selection pressures that drove our brains to increase in size prior to the rise of agriculture.

[00:50:10] David explains how population density relates to brain size.

[00:52:20] Ken asks if the shrinkage of the human brain, which has decreased from 1,500 cubic centimeters to 1,350 cubic centimeters, is found in all locations and populations.

[00:53:01] David describes why he believes that the available evidence supports the notion that our smaller brains equate to less intelligence, or less capacity for intelligence.

[00:56:11] Ken asks if mitochondrial function has changed since the agricultural revolution.

[00:57:02] Ken asks if there is a “worst case scenario” with regards to AI and our increasing dependence upon it, asking if with continuing to off-load evolutionary pressure on brain size and cognitive capacity onto our technology.

[01:02:32] Dawn asks about David’s book Male, Female: The Evolution of Human Sex Differences, and how it has been described as the first comprehensive evolutionary model to analyze sex differences and how they have evolved by means of sexual selection.

[01:05:34] David elaborates on his words in an interview with The Guardian, where he said “People talk about cultural factors creating sex differences. I think it’s the other way around: There’s pressure to disconfirm the way people are. Cultural hype tries to make the sexes more alike, which is stressful for boys and girls and men and women.”

[01:08:55] Dawn mentions that David is perhaps the first academic to frame biological sex differences in terms of their vulnerability. She asks him why he believes that this approach could transform science and medicine.

[01:11:56] David discusses the Basic Index of Gender Inequality, which was devised in partnership with Gigster Stoet of the University of Essex in the UK. He describes why the index as a new measurement tool is fairer to both men and women. He talks about how the index presents a simplified but more accurate picture of people’s well-being than measurements like the World Economic Forum’s Gender Gap Index.

[01:16:55] Ken mentions that David’s index marks Italy and Israel as the two most egalitarian nations in regards to gender, with the United States placing at number 61 of 134.

[01:18:00] Ken asks why it is that Saudi Arabia is listed as the third-most gender egalitarian nation on the index.

[01:19:41] Dawn asks about David’s other projects in evolutionary psychology, that range from the study of social signaling, and mate quality, to sex differences in face perception.

[01:22:06] David ends the interview talking about what he does with his spare time.


David Geary bio

MU Math Study

David Geary Amazon page

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Ken Ford bio

Dawn Kernagis bio