Theory 026/Life & Evolution /Domestication
Domestication Is a Fear Threshold
Domestication is described as selection for tameness. Tameness may be one visible consequence of a shifted threshold.
Domestication is the consequence of selection on a fear-response threshold rather than on tameness itself, so the suite of correlated changes in domesticated animals follows from a single shift in the threshold.
01The evidence
Domestication produces a correlated suite of changes in coat, skull, reproduction and behaviour, and selecting on tameness alone reproduces much of the suite.
02The tension
The correlated suite is usually explained by pleiotropy, which names the pattern but not the reason it clusters around behaviour. A threshold account supplies the reason.
03The mechanism
Fear responses are threshold-based: a stimulus either exceeds the flight threshold or does not. Lowering the threshold makes animals flee more; raising it makes them approach humans without any change to a separate tameness trait.
Because the threshold is set by neuroendocrine systems that also regulate stress, reproduction and pigmentation, shifting it produces the correlated suite.
04What this is not
Those accounts name the trait and the correlation. This names the threshold that produces both, which predicts the suite from one parameter.
05Predictions
- P1Selection on the threshold should reproduce the suite.
- P2Wild species with naturally high thresholds should domesticate faster.
- P3The suite should appear together rather than sequentially.
06Refutation
Domestication traits appearing independently of threshold shifts would weaken the single-parameter account.
07What it changes
It would predict which species can be domesticated.