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Individuals with darker pigmentation are found to be pleiotropically linked to higher levels of aggression, sexuality, and social dominance than individuals with lighter pigmentation

Ducrest et al. (2008) reviewed data on over 40 wild vertebrate species showing that within each species,darker pigmented individuals averaged higher levels of aggression and sexual activity than lighter pigmented individuals, with a larger body mass, more resistance to stress, and greater physical activity when grooming.

The relationship between coloring and behavioral dominance was robust across three species of mammal (African lion, soay sheep, and white-tailed deer), four species of fish (mosquito fish, guppy, green swordtail, and Arctic charr), four species of reptile(asp viper, adder, fence lizard, and spiny lizard), one amphibian species (spadefoot toad) and 36 species of bird.

In captive Hermann’s tortoises (Eurotestudo boettgeri), another reptile species, Mafli, Wakamatsu, and Roulin (2011) found darker shell coloration predicted greater aggressiveness and boldness. Darker individuals were more aggressive in male–male confrontations and bolder towards humans, independent of body size and ******t temperature. (Melanin based color traits are a criterion in mate choice.)

Male lions with darker manes remained more aggressive and sexually active than those with lighter manes, and darker feathered barn owls continued to have a stronger immune response to stress than lighter feathered barn owls.

Pigmentation change in wild silver foxes (Vulpes vulpes) was one outcome of breeding for tameness. It was the Russian geneticist Belyaev (1917–1986) who found that selecting easy-to-handle foxes pulled along with it many features that distinguish domestic animals from their wild forebears including white patches in the fur, droopy ears, a smaller skull, and a faster reproductive cycle(Trut, 2003; Trut, Iliushina, Prasolova, & Kim, 1997). Domesticated foxes reached sexual maturity a month earlier (at 7 months) than non-domesticated foxes, and gave birth to litters averaging one pup larger (about six). After 40 years and the breeding of 45,000foxes, Belyaev’s successor, Trut (2003) had animals as tame and eager to please as a dog.

The pattern of coat color that had evolved as camouflage in the wild, depigmented to piebold, one of the most striking mutations among domestic animals and seen frequently in dogs, cats, sheep, donkeys, horses, pigs, goats, mice, and cattle.

Similar effects of de-pigmentation have been found in laboratory rats, which are typically albinos with white coats and pink eyes. Black rats are more aggressive (and so also make poorer pets).However, black rats with white spots (from the ‘‘white spotting gene’’) are calmer and more easily handled. A 15-year study of selection for tameness over 30 generations in wild Norway rats(Rattus norvegicus) found the percentage of piebald rats increased rapidly until over 70% had white bellies and about 50% had white feet and ankles or ‘‘socks’’ as they are called (Trut et al., 1997). In this experiment in rats, selection for tameness correlated with their depigmentation.

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