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Welcome to Pleiotrope, my new blog. I’m an evolutionary psychologist at the University of New Mexico, and I’m interested in all aspects of intelligent life.
Why “Pleiotrope”? At first glance, it’s a bad name for a blog, almost as obscure and pretentious as PZ Myers’ “Pharyngula”. Almost nobody knows what Pleiotrope means, or how to spell it or pronounce it.
But I like how Pleiotrope sounds, and it has a couple of meanings that highlight this blog’s themes.
Technically, a pleiotrope is a gene that influences many traits – including traits that seem unrelated at first. For example, the BRCA1 gene is famous because its mutations predict about 5-10 percent of all breast cancers, so women with family histories of breast cancer should get the genetic test for BRCA1 mutations. When BRCA1 works normally, it controls the growth of cells that line the milk ducts of the breast, suppressing tumors. But its evolutionary function is much more general – it helps repair DNA breaks throughout the genome and helps destroys damaged cells throughout the body. So BRCA1 interacts with at least 50 other genes, and BRCA1 mutations influence many other forms of cancer (ovarian, prostate, pancreatic, colon, leukemia). Yet BRCA1’s influences don’t stop there. Some BRCA1 mutations (such as 187delAG, which has its own facebook group) seem to have been favored by selection for thousands of years, and unleash neural growth in embryos, apparently increasing intelligence in some populations. So, mutations like that seem to have a tricky mix of costs (higher breast cancer risk) and benefits (higher intelligence). That’s pleiotropy.
Genes influence mobile phone use
As another example, my Brisbane collaborators and I just published a new paper about genetic influences on mobile phone use.In two samples totalling 1,036 individuals, we found that genes influence about 34 percent to 60 percent of the variation in how often Australian teenagers talk and text on their mobile phones. (Surprisingly, shared family environment, including parental wealth and education, had virtually zero effect on teens' mobile phone use.) It may sound weird that ancient genes could influence use of a technology that's only been around for two generations. But behavior geneticists have found moderate heritabilities like this for every behavioral trait that can be measured reliably, including use of other evolutionarily novel technologies like reading books and watching TV and liking dark chocolate. Probably the genes are influencing basic cognitive traits like intelligence, personality traits like openness, and sensory traits like taste preferences, and these in turn are influencing product use. More than 5.8 billion people now use mobile phones, so we thought this was a nice demonstration that genes, not just family environment and culture, can be important in consumer behavior.
The pleiotropy comes in here: we also found a slight negative genetic correlation between mobile phone use and intelligence. That is, some of the same genes that make you brighter also tend to make you spend fewer minutes per day talking or texting on your phone. This might be because brighter teens have less interest in idle gossip, or maybe those with higher verbal intelligence can communicate more efficiently, using fewer words per message. We couldn't tell from our data. Nor could we identify which specific genes (probably thousands of genes) influence both traits. But the behavior genetic modeling can tell us that there is a definite genetic overlap between the traits. So pleiotropy doesn't just affect physical traits like cancer; it also affects mental traits like intelligence, and social and technological traits like mobile phone use.
Typical genetic architecture
Pleiotropy is cool because it highlights the integrity of body and mind. Different kinds of cells and tissues share most of the same biochemistry, so the genes that build our core biochemistry and neurophysiology have pervasive effects throughout our bodies and brains. Good evolutionary psychologists and behavior geneticists do not believe in one gene per trait, the way that some critics of “genetic determinism” claim. Rather, we undestand that the "genetic architecture" linking genes to traits is very complex, with each gene influencing many traits (pleiotropy), and each trait being influenced by many genes (polygeny).
Appreciating pleiotropy need not drive us to sappy New Age holism. It doesn’t require us to use the term “inextricable” whenever discussing nature and nurture, like some sophomore postmodernist. On the contrary, pleiotropy lets us make powerful and startling predictions about why traits hang together – like why all reliable mental tests correlate positively to yield something called “general intelligence”, or why most medical tests correlate to yield something called “health”.
Apart from this technical genetic meaning, a "pleiotrope" at the metaphorical level can mean any hidden cause that has many diverse effects. An underlying variable that drives a lot of superficial correlations. A simple model that explains a lot of complexity. A consilient theory that explains diverse findings.
I like going pleiotrope-hunting and trying to find the key parameters that explain most of the variance. When we scientists find pleiotropes that seem exciting, I think we have a duty to tell folks about them. That’s why I’m starting this blog.
