4.2 Experimental domestication of foxes
In 1959, the Russian geneticist Dmitri K. Belyaev (1917–1985) launched a long-term experiment to tame captive-bred red foxes by selecting for a single behavioural trait: lack of fear and aggression towards humans. Over 40 years, more than 45 000 foxes were bred in captivity at a remote farm near Novosibirsk, Siberia. Various behavioural, physiological and morphological characters were studied in each fox. Selection for tameness was strict: each animal was assessed once a month for seven months for its willingness to approach people, take food from human hands and be stroked (Figure 13b). Only the tamest 5 per cent of males and 20 per cent of females of each generation were allowed to breed. The control population was bred randomly with respect to their behaviour with people.
Are these levels of artificial selection strong compared with natural selection measured in wild populations?
Yes, very strong. In natural populations, the chances of survival and successful reproduction of individuals with or without particular traits usually differ by only a few per cent, i.e. selection coefficients are much less than 1.
Selection at this level in small isolated populations is likely to make some inbreeding unavoidable.
What simple intervention would reduce inbreeding?
Eliminating breeding between the brothers and sisters.
By applying this rule in each generation, inbreeding was maintained at about 3–7 per cent (compared to around 12 per cent in many contemporary pedigree dogs).
What evidence would show that the change in behaviour had a genetic basis?
A strong response to selection in the form of greater frequency of tameness behaviour in the offspring of foxes selected for this trait.
The experimenters found that after 10 generations, 18 per cent of the foxes in the selected population showed clear signs of tameness. They approached and licked people, wagged their tails, whined and begged for food offered by hand. After 20 generations, the proportion of foxes showing this kind of behaviour had risen to 35 per cent, clear evidence of response to selection for inherited traits.
Using the theory and terms developed for the study of natural selection, was artificial selection for tameness in the fox experiment:
(a) stronger in male or female foxes?
(b) directional, stabilising or diversifying?
(c) promoting or reducing genetic diversity in the population?
(d) operating in the same direction as or opposing natural selection?
(a) Males, as a smaller proportion of each generation were allowed to breed.
(b) Selection for tameness was strongly directional because the same character was favoured in each generation.
(c) Such a small proportion of the population was allowed to breed that genetic diversity must have been reduced.
(d) Natural selection favours adaptations that enable animals to thrive in the wild; the artificial selection opposes such natural selection by making the foxes less afraid of large potential predators such as people, and by favouring coat colours and temperaments that reduce their ability to find and catch their own food.