Belyaev and Trut found in their farm-fox experiment that
critical period changes could be seen in sight, hearing, fear
response, and bonding (Figure from Trut
Implictions for the evolution of dogs
Researchers posit that similar changes probably occurred
evolution of dogs. Animal that could better bond with humans may have
been selected for by the environment or by artificial
selection. A longer socialization period could have led
to more dogs being tamed.
Example: Object permanence (Hare
& Tomasello, 2005)
The task consists of understanding that something
which is out of sight
still exists. Dogs also perform well on this task, a surprising finding
as other non-human primates such as the chimpanzee (the closest human
relative) do not do well in this type of evaluation. What’s
dogs are able to use the actions of humans to aid them in the
uncovering of hidden objects. When an experimenter
points, stares, or uses a novel cue (such as block marker) to delineate
where a treat is hidden, dogs, even puppies, can use these
interspecies cues to find the treat.
dog can tell the difference between different human social
cues. If an experimenter
stands closer to one hiding spot but looks at another or turns their
head towards one but fixes their eyes elsewhere, dogs interpret these
signals only in terms of gaze. This ability of dogs to use
human social cues appears
early in life and are robust in all breeds and in dogs raised with and
without human attention.
Puppy using human
social cues to find a treat (Pennisi 2002).
Some researchers have suggested that this may have been
by convergent evolution between dog and man. One idea is that this
might take the form of predisposition of certain animals to be able to
absorb human signals during rearing with humans. This could explain why
some chimps (those raised by humans) perform significantly better than
others in tests of using human cues to find hidden objects. But this
does not bear out in dog studies.
- First, young puppies show this effect
just as robustly as older dogs. (See figure).
- Second, there does not appear to be any
difference in dogs raised with humans (in a home, with a trainer, etc)
and those raised with other dogs (shelters) in terms of social cue
reading. (Hare & Tomasello, 2005)
Inherited social cues
Wolvesare pack animals that fight as a group and so
using social cues in the
search for prey could have evolved long before the wolf/dog
split. This theory has been disproven. Wolves, even those raised by
humans, are unable to use human social
cues as dogs do to find hidden food. Because wolves do not have the
ability to interpret human social cues, there is no way that dogs could
have inherited this ability from wolves.
Domestication as a cause
Dogs’ ability to tune into social cues may have evolved when
being domesticated. The domesticated
farm-foxes show the same abilities that dogs show (that neither wolves
non-domesticated foxes have) which would support the idea that use of
social cues evolved during domestication (Trut 1999).