Ladies: if you are marrying a man born in the winter, keep a closer eye on him than if you are marrying a man born in the summer, fall, or spring.
Gabriel Max, “The Lion Bride,” (via NYPL Digital Gallery)
Men having “thrill-seeking” genes who are born in winter are more “venturesome” than those born at other times of the year.
All this is according to a recent Public Library of Science report that being born in winter turbo-charges the genetic predisposition toward thrill-seeking. The report found that winter-birthday x genes = extra risk taking, at least in the US college-age population studied.
“Season of birth” – or, “SOB” (no joke, the acronym is “SOB”) has been tossed around as relevant to behavior later in life. (More after the jump)
“Venturesomeness” as a behavioral trait (there’s apparently a test) is amplified in men having “risky” dopamine genes when they are born in winter.
Compare the white bars — these are the ones with the “risky” dopamine receptor alleles (“L+”). Men carrying the “risky” gene are more “venturesome” when born in winter. (The authors said the male data held for another dopamine receptor allele, the DRD2 allelic variant associated with addiction, but didn’t show the data).
Lots more after the jump
The data didn’t correlate for females, although the authors reference data from Sweden that “those born during February to April were significantly more likely than those born during October to January to have high NS (novelty seeking) among women, particularly the subscale NS2 (impulsiveness vs. reflection), and to have high PS (persistence) among men.”(This is a quote from the Swedish abstract.)
Backing up a bit, here is a graph of where people have the “risky behavior” or novelty seeking dopamine allele. (The link has an easier to read version).
DRD4R7 Allelic Frequency (via the Allelic Frequency Database)
The yellow portion is the “7″ allele because there’s a DNA that is repeated 7 times within the gene, possibly making dopamine more difficult to bind to the receptor protein — hence, the need for dopamine — like the need to drive fast or bungee jump.
Look at South American and Northern European populations — both of which have higher frequencies of the dopamine receptor allele that is correlated with risky behavior. The “risky” dopamine receptor allele (yellow bar, DRD4R7) may have been selected for during the last ice age, a time of great human migration. You don’t want a Caspar Milquetoast tagging along as you’re crossing an ice bridge from Siberia to Alaska.
The pockets of high- thrill seeking dopamine genes are those that are at the end of the human -migratory line — fairly unhospitable places, perhaps blocked by mountains or oceans. Cold weather (the Northern Europeans), equatorial (the South Americans), or extreme changes in weather (the American Indians of the Southwest U.S.) all have a fair amount of the “yellow” (the “7 repeat” version of DRD4).
Why would being born in winter amplify “venturesome-ness” later in life? The authors postulate some reasons — natural mammalian response to sunlight duration, maternal stress in utero, large scale climate change engendering lots of neural plasticity.
My own bias is probably the neural plasticity theory — my view is that people are evolving to be supremely adaptable, not to go into niches. (This relates to my previous post about protein de-evolution to be less species specific.) The authors speculate about this, and as long as we’re all speculating, I would tend to vote with this:
. . .On a smaller timescale, over the last millennium of Chinese history, climate changes to cold phases have been associated with decreased harvests, increased warfare, decreasing population and dynastic changes . . . While very speculative, it is possible that physiological and behavioral plasticity based on birth environment allows better survival through such turbulent changes.
Season of Birth and Dopamine Receptor Gene Associations with Impulsivity, Sensation Seeking and Reproductive Behaviors
1 Department of Anthropology, Northwestern University, Evanston, Illinois, United States of America, 2 Department of Anthropology, State University of New York at Binghamton, Binghamton, New York, United States of America, 3 Department of Biology, State University of New York at Binghamton, Binghamton, New York, United States of America, 4 Laboratory of Evolutionary Anthropology and Health, State University of New York at Binghamton, Binghamton, New York, United States of America, 5 Department of Anthropology, University of Wisconsin Milwaukee, Milwaukee, Wisconsin, United States of America, 6 Department of Psychology, State University of New York at Binghamton, Binghamton, New York, United States of America, 7 Center for Alcohol and Addiction Studies, Brown University, Providence, Rhode Island, United States of America
Abstract
Background
Season of birth (SOB) has been associated with many physiological and psychological traits including novelty seeking and sensation seeking. Similar traits have been associated with genetic polymorphisms in the dopamine system. SOB and dopamine receptor genetic polymorphisms may independently and interactively influence similar behaviors through their common effects on the dopaminergic system.
Methodology/Principal Findings
Based on a sample of 195 subjects, we examined whether SOB was associated with impulsivity, sensation seeking and reproductive behaviors. Additionally we examined potential interactions of dopamine receptor genes with SOB for the same set of traits. Phenotypes were evaluated using the Sociosexual Orientation Inventory, the Barratt Impulsivity Scale, the Eysenck Impulsivity Questionnaire, the Sensation Seeking Scale, and the Delay Discounting Task. Subjects were also asked about their age at first sex as well as their desired age at the birth of their first child. The dopamine gene polymorphisms examined were Dopamine Receptor D2 (DRD2) TaqI A and D4 (DRD4) 48 bp VNTR. Primary analyses included factorial gender×SOB ANOVAs or binary logistic regression models for each dependent trait. Secondary analysis extended the factorial models by also including DRD2 and DRD4 genotypes as independent variables. Winter-born males were more sensation seeking than non-winter born males. In factorial models including both genotype and season of birth as variables, two previously unobserved effects were discovered: (1) a SOB×DRD4 interaction effect on venturesomeness and (2) a DRD2×DRD4 interaction effect on sensation seeking.
Conclusion
These results are consistent with past findings that SOB is related to sensation seeking. Additionally, these results provide tentative support for the hypothesis that SOB modifies the behavioral expression of dopaminergic genetic polymorphism. These findings suggest that SOB should be included in future studies of risky behaviors and behavioral genetic studies of the dopamine system.
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