Cognition. Intelligence. Emotion. Sexuality. These are not merely complicated traits, invoking awed respect. These are aspects of animal life and human nature that are daunting in their biological complexity and in their existential importance. Curious biologists have been tackling animal behavior for centuries, but some topics and behaviors still remain opaque to biological understanding. While the demystification of human nature might give some unease, more of us are simply skeptical of any attempt to unravel the genetic underpinnings of such things.
For years now, genome-wide association studies (GWAS) have been mining ever-growing genetic datasets for clues to the genetic bases of complex traits and diseases that include behaviors and disabilities in cognition, intelligence, sexuality, social interaction, and emotion. Along with a few breakthroughs, there have been significant disappointments and legitimate questions about the limits of potential success (Visscher et al., 2012).
Some geneticists don’t seem to have gotten the memo.
Discussing the biology of human intelligence is a good way to start a scholarly brawl, and yet this complex trait is strongly heritable. Previous GWAS have found hints and candidates for causative genes, but the results are thought to be statistically underpowered. However, in May an international collaborative group published a large meta-analysis of data combined from these previous GWAS (and with new data), and reported 30 new and very promising candidate genes influencing human intelligence (Sniekers et al., 2017). By increasing the cohort (nearly 80,000 people) and using some new tools (such as MAGMA), the work substantially expanded the list of genetic players. One new candidate is FOXO3, a transcription factor involved in insulin/IGF signaling.
What of love? Shakespeare claimed that the course of true love never did run smooth, but geneticists recently claimed that assortative mating occurs in humans, meaning that humans tend to select mates that resemble themselves to some extent (Robinson et al., 2017). This operates phenotypically, separate from confounding influences (such as socialization), and has implications for human population genetics and evolution. Another recent report found 12 genes associated with human reproductive behavior, specifically age at first birth and number of children (Barban et al., 2016). Romantic.
Not even parenting practices are sacred. Hopi Hoekstra and her group study the evolution and genetics of behavior in closely related species of mice—the mice exhibit significant behavioral differences but can interbreed. This facilitates quantitative genetics and whole-genome analysis of behavioral traits. In a paper in April, the group reports on the genetics of parenting (Bendesky et al., 2017). Their tour de force showed heritability of a suite of parental behaviors (such as nest-making and baby-licking) and then dissected the genetic infrastructure. Even though the behaviors seem very similar in males and females, the underlying genetics can differ significantly. One behavior, nest-building, stands out, both because it seems genetically independent of other parenting tasks and because it has evolved through changes in the expression of vasopressin.
Quantitative genetics is bringing powerful tools to old questions, including some deemed sacred or hopelessly complex. More drama is certain to come. Be sure to get a good seat.