The Anna Karenina Principle and the Nature of Domestication

Key Insight

The Anna Karenina principle asserts that for success in complex endeavors, such as a happy marriage or animal domestication, numerous conditions must be met simultaneously, while failure can arise from a single deficiency. This concept challenges the common search for simplistic, single-factor explanations for success. Applied to animal domestication, it elucidates why many seemingly suitable large wild mammal species, including zebras and peccaries, have never been domesticated, highlighting that successful domestication is an exceptionally rare outcome requiring compatibility across multiple crucial factors.

A domesticated animal is defined as a species selectively bred in captivity, resulting in modifications from its wild ancestors, with humans controlling its breeding and food supply. This distinguishes it from merely 'tamed' animals, like elephants used for work, which are wild-caught individuals. Domestication involves profound changes, such as alterations in size (e.g., cows, pigs, sheep became smaller; guinea pigs larger), retention of wool (sheep, alpacas), increased milk yields, and reduced brain and sense organ development, as animals no longer require the survival instincts of their wild counterparts. The vast diversity in dog breeds, from Great Danes to Pekingese, compared to their wolf ancestors, exemplifies these human-driven evolutionary changes.

Evidence for this principle is robust. All big mammal species amenable to domestication were rapidly integrated into human societies between approximately 8000 and 2500 B.C., within the initial few millennia of sedentary farming-herding. Since 2500 B.C., there have been no significant new additions to large mammal domesticates. Modern scientific efforts to domesticate large mammals, such as eland, elk, moose, musk ox, zebra, and American bison, have yielded only limited economic success, despite advanced genetic and breeding techniques. This strongly indicates that inherent biological and behavioral shortcomings of candidate species, rather than any cultural or technological limitations of ancient or modern humans, account for the vast majority of domestication failures.