Behavioural Evolution and Domestication

Domestication has many different definitions:

• ”Evolution of a nonhuman population in response to an anthropogenic niche”

• ” …a domestic population is one that cannot sustain itself outside that niche”

• “A process in which species are selected to live in human-controlled environments”

• “A process in which humans deliberately and with forethought assume control over the domesticate's movement, feeding, protection, distribution, and, above all, its breeding—directed at achieving specific clearly identified goals”

Taming vs domestication

Taming:

• An individual-level, non heritable process

• Happens within a single animal’s lifetime through habituation or conditioning

• Purely behavioural, no genetic change to the species or population

• Not passed to offspring: a tame individuals young are not born tame

• Can apply to any species, including non-domesticates (e.g., hand-raised or rehabilitated wildlife)

Domestication:

• Population-level, evolutionary process across many generations

• Heritable - genetic change is passed on to offspring whether or not they are ever handled by a person

• Driven by selection (natural, artificial, or both) acting on a population over time, typically in response to a new anthropogenic niche

• Only a small number of species have ever been domesticated, despite far more having been individually tamed

Taming of individuals does not accumulate into domestication. However, continuous expression of tameness within a population might, because then selection has something to act on across generations.

taming vs tameness

Taming is a human action, tameness is a behavioural trait (can be selected upon)

Domestication is tameness + (…)

• Reproductive isolation

  • a founder population breeds under human conditions not in the wild

• Multi-generational selection

  • even with no deliberate breeding goals, selection happens in a captive/commensal environment, e.g. relaxed predator predation pressure, increased human-proximity, changed diet, changed group composition. Darwin called this unconscious selection

Pathways to domestication

• Commensal

• Prey

• Direct

Commensal pathway to domestication

A species voluntarily enters the human niche, drawn by food or shelter.

Prey pathway to domestication

Managed hunting gradually becomes controlled breeding

Directed pathway to domestication

Deliberate capture of a wild species for a specific purpose

What are some factors that make animals more or less predisposed to domestication?

Pros:

• Large gregarious groups

• Non-territorial

• Promiscuous mating system

• Precocial young

• Generalist feeders

• Short flight distance from humans

• Low reactivity to novelty

Cons:

• Family groups

• Territorial

• Monogamous mating system

• Altricial young

• Specialist feeders

• Wariness and long flight distances

• High sensitivity to novelty

Dog domestication:

• First documented species to be domesticated

• The dog remains the only domesticated large carnivore

• Domestication of the dog was not instigated by deliberate human action

• A few hypotheses of how they were domesticated:

  • Commensal scavenger hypothesis of wolf domestication

  • Cross-species adoption

The commensal scavenger hypothesis of wolf domestication

Wolves scavenging refuse around human settlements gained access to a new, stable food niche. The least fearful individuals thrived and over generations this diverging population became commensal, eventually adapting further to life alongside humans

Natural Selection, Not Human Direction

• Ancestral wolves varied in fearfulness toward novel stimuli

• Reduced fearfulness in some wolves did not evolve for exploiting the new human niche – it was already present

• That is: Less fearful wolves were pre-adapted to exploit this new resource

• This is called exaptation: an old trait is used in a new context

exaptation

An old trait that is already present is used in a new context

Cross-species adoption hypothesis of wolf domestication

probably not true according to Christina, taming is not transferred to offspring and its really hard to tame wolves even still today

• Pleistocene people may have captured and hand-reared wolf pups

• Pet-keeping is widespread among hunter gatherer societies

• Ice Age human populations may have been too small and dispersed to sustain a scavenger population

Domestication syndrome

The general alteration of 1) morphological, 2) physiological, and 3) behavioural traits that occurs simultaneously in domesticated animals

• White pigmentation more common

• Curly tail

• Floppy ears

• Less aggressive

• Less fearful

• More playful

Domestication traits vs improvement traits

Domestication traits:

• Essential at the early stages of domestication

• Generally shared across all domesticates of a species

• Under selection during the initial stages of domestication. In animals, these traits will primarily be behavioural, e.g.:

  • Tameness

  • Low reactivity

  • Tolerance of restricted space/movement

• Often (partly) a relaxation of natural selection, not only positive selection.

Improvement traits:

• Arose after the initial stages of domestication

• Present in only a proportion of domesticates - often fixed within particular breeds or regional populations

• Product of later, increasingly deliberate (artificial) selection, e.g.:

  • Milk yield,

  • Egg number

  • Body size

  • Specific coat colours

  • Specific behaviours (e.g., herding)

Methods to quantify behavioural evolution

• Common garden — raise both populations in the same environment. A difference that persists indicates genetic differentiation

• Cross-fostering — allows the separation of genotype, environment and parental effects

• Selection experiment — a response to selection across generations is evolved change by definition