Mice & digit ratio

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Selective Breeding for a Behavioral Trait Changes Digit Ratio:

The ratio of the length of the second digit (index finger) divided by the fourth digit (ring finger) tends to be lower in men than in women. This 2D:4D digit ratio is often used as a proxy for prenatal androgen exposure in studies of human health and behavior. For example, 2D:4D ratio is lower (i.e. more ‘masculinized’) in both men and women of greater physical fitness and/or sporting ability. Lab mice have also shown variation in 2D:4D as a function of uterine environment, and mouse digit ratios seem also to correlate with behavioral traits, including daily activity levels. Selective breeding for increased rates of voluntary exercise (wheel running) in four lines of mice has caused correlated increases in aerobic exercise capacity, circulating corticosterone level, and predatory aggression. Here, we show that this selection regime has also increased 2D:4D. This apparent ‘feminization’ in mice is opposite to the relationship seen between 2D:4D and physical fitness in human beings. The present results are difficult to reconcile with the notion that 2D:4D is an effective proxy for prenatal androgen exposure; instead, it may more accurately reflect effects of glucocorticoids, or other factors that regulate any of many genes.

One Comments

  1. Note 42 says that female mice run more. Data on the students(8) suggests there is a parallel with women. It’s my impression that human females are more likely to use a treadmill or ever buy one for home use. Activities like those are not the same as typical rough and tumble masculinised behaviour in humans or, I dare say, mice. 
     
    How common is the behavior the high digit ratio mice were exibiting, “predatory aggression”, in female mice. Increased neuroticism in feminised mice may cause increased biting of handlers. 
     
    Professor Manning (the 2f4f man) discusses glucocorticoids having some conection to the ratio in his latest book. It is not more important than testosterone going by this study though.

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