Following on from the work of ethologists such as Konrad Lorenz, biologists and psychologists have carried out a lot of research into how baby chicks and ducklings become attached to their mothers. Chicks can see as soon as they are born and quickly learn to recognise their mother or at least their supposed mother. If the real mother is absent, they even become attached to inanimate objects. This makes possible all sorts of behavioural experiments. Up to now, it was unclear how new-born mammals, including human babies, become attached to their mother. A project to clarify this matter therefore was subsidized by the NWO's Social Science Research Council (MAGW). Psychologists at Nijmegen University and biologists at the University of Groningen have now identified interesting behavioural differences between chicks and mammals.
Experiments with guinea pigs which grew up in isolation with a lifeless object as their surrogate mother showed that the young guinea pigs were not attached to the object. They were not distressed when separated from it, nor did they prefer their "own" object to a novel one. Guinea pigs of a few days old did not distinguish between their actual mother and other lactating females.
The researchers then took baby rats which are blind for the first 12 days and reared them with their mother but separately from other adults. Between 10 and 30 days, the baby rats were required to repeatedly choose between wire cages containing the mother, another lactating female, a lactating female of a different colour, a non-lactating female, a male rat, or an empty cage.
The young rats chose other lactating females just as frequently as their actual mother but they went to the lactating females more frequently than to the female without milk. They preferred the latter to the male and the male to the empty cage. It would appear that young rats react to the scent of lactating females but do not yet recognise their mother. Fear of rats other than their own mother seems not to play a role because otherwise they would avoid unknown animals and prefer the empty cage.
Because most mammal mothers make a clear distinction between their own progeny and those of other mothers, it is vital for the young to learn which particular animal is their mother. In an environment where more than one mother is present, they have to learn this very quickly. Instinct alone is insufficient. The learning process presumably is based on trial and error.
Martine Janzen (Nijmegen University)
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Dr Paul Timmermans
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