How do birds learn to build their nests?
Birds do not learn how to build their nests. They already know! At nest-building time fledglings brought up in artificial conditions build nests to the design normally followed by that particular species. The art of building what will be their babies' cradle is not passed on by example or practice, but is part of their hereditary or genetic programme- as are the colors of their feathers and the shape of their beaks.
We have to learn, and sometimes with a great deal of effort, almost everything we need for living, and this inborn memory seems both wonderful and mysterious to us. Just think how much more simple life would be if our parents could teach us a foreign language which our children would then inherit without having to learn it.
We are nowhere near being able to do this! A baby with French parents, brought up by English people, will speak English and will have to learn French just like native English babies.
How are these abilities passed from generation to generation?
Many experiments have been carried out to discover the secret of this inborn knowledge. Since these skills are passed on along with the species' physical characteristics, scientists deduced that they were in some form of 'code' (a code is a system of signs by which messages can be transmitted) as were the bird's size, the shape of its eyes and so on, in the very complex chemical substances that are found in every cell. It is these 'chains', split into filaments of varying lengths, that carry the hereditary programme.
An experiment carried out on animals very different from birds-flatworms-has shown that certain information can in fact be transmitted in this way. Flatworms were taught to fetch food from a particular spot. The chemical substances making up the signs of the hereditary code were then taken out of the flatworms which had been trained.
They were then injected into the untrained flatworms: these then had no difficulty in finding the food!
So knowledge vital to the survival of the species can be inherited. A bird knows how to build its nest just as a baby knows how to suck the breast.