Beware the dark-eyed

By Razib Khan | August 18, 2008 12:50 am

p-ter points me to a new paper in Trends in Ecology, Pleiotropy in the melanocortin system, coloration and behavioural syndromes:

In vertebrates, melanin-based coloration is often associated with variation in physiological and behavioural traits. We propose that this association stems from pleiotropic effects of the genes regulating the synthesis of brown to black eumelanin. The most important regulators are the melanocortin 1 receptor and its ligands, the melanocortin agonists and the agouti-signalling protein antagonist. On the basis of the physiological and behavioural functions of the melanocortins, we predict five categories of traits correlated with melanin-based coloration. A review of the literature indeed reveals that, as predicted, darker wild vertebrates are more aggressive, sexually active and resistant to stress than lighter individuals. Pleiotropic effects of the melanocortins might thus account for the widespread covariance between melanin-based coloration and other phenotypic traits in vertebrates.

Catherine_Zeta_Zones_05.jpgThe fact that blondes have more fear and redheads feel more pain might make some more sense. Skin color seems to have gotten lighter over the past 5-20 thousand years across northern Eurasia by substitutions and changes in frequency on a few loci of large effect. Evolutionarily this predicts that pleiotropy will product side effect phenotypes before modifier genes can arise to mask the deleterious byproducts of said evolution.

  • Bob O’H

    “Trends in Ecology”? Have the TREE editors become creationists and dropped evolution? :-)

  • Simon

    I must admit Catherine Zeta Jones looks REAL scary ….

  • beebeeo

    However, within the paper the authors state: “it is important to note that variation in melanin-based coloration between human populations is primarily due to mutations at, for example, MC1R, TYR, MATP and SLC24A5 and that human populations are therefore not expected to consistently exhibit the associations between melanin-based coloration and the physiological and behavioural traits reported in our study”

  • razib

    p-ter sayeth:
    However, they may be unaware that some difference in pigmentation both between and within populations is controlled by ASIP, a protein that binds MC1R, acting as an antagonsist for melanocortin binding. Humans, then, could be an ideal test case for the hypothesis–do phenotypes like aggression map to ASIP like pigmentation does? However, the unpalatable nature of this question makes it rather unlikely to be pursued in humans.

  • Ross

    “melanin-based coloration is often associated with variation in physiological and behavioural traits”
    Please don’t let James Watson come anywhere near this research.

  • NatalieSpa

    Do you know if any of those pre-mentioned genes link to genes or are the ones for schizo-affective disorder/s or addiction, anorexia and sleep “disorders”..? I did a little experiment at home with the amino-acid “tyrosine” and found that it made me more confident but aggressive. I know it’s the precurssor to dopamine, sorry I’m not a scientist, I’m a consumer but aggression must be a normal trait for carnivorous mammals to have.. also, it is adaptogenic and helps you think quicker and be stronger and more sexually active. I’m posting this here because I read once or twice that certain drugs cling longer to melanin hence an increased risk of addiction, and I know that the amino acids/neurotransmitters found in abundance in red meat, chocolate (!) and that are produced during love are one and the same..!!


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Gene Expression

This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


See More


RSS Razib’s Pinboard

Edifying books

Collapse bottom bar