Kelly Johnson, age 9, of Des Moines, Iowa, for his question:
Why don't cuckoos take care of their own eggs?
When your parents were young and going to school, they were told that animals are ruled by instincts. In those days, scientists said that instinct explained just about everything that animals do. Most people thought that instinct was a sort of built in voice of Mother Nature. It told the birds and other animals just what to do and they had to obey. For example, they thought that instinct instructed most birds to be devoted parents but a few other birds were instructed to place their children out for adoption.
In the past, people used the word instinct to explain a multitude of animal mysteries. But modern scientists do not use the word at all. This is because they have solved the basic mystery of animal behavior. The secret is a marvelous chemical with the amazing name of deoxyribonucleic acid. The shorthand for this outlandish word is TINA. It is a miraculous biochemical that governs the life of every animal ¬what he looks like and what he does. DNA instructs certain cuckoos to place their eggs in the nests of other birds.
Nobody really knew what instinct was like or how it worked. But modern scientists do know what DNA molecules are like and even how their atoms are arranged. They also know where its blueprint pattern came from, how it gives the orders and why every animal must obey them.
A new animal begins when cells from two parents merge. Each new animal inherits half its DNA from each parent. It is there in a bird's egg and as the embryo develops, a copy of its DNA is included in every new cell. It orders every step as the young bird grows its shape and size, its color and just how it should behave at all times.
A computer is a non living machine. A human expert puts in data to program it to do this or that. Although DNA is a miraculous living substance, in some ways it acts like a super computer. It programs all birds to mate and lay eggs. It instructs most birds to build nests and become devoted parents. The cowbird and certain cuckoos are instructed to mate and lay eggs. But their DNA is not programmed for parenthood.
After mating, the females place their eggs in other bird nests. There they are adopted by foster parents who raise them with their own chicks. These birds are programmed to provide shelter and food and educate their little ones. Their own children inherit these good qualities with the DNA from their parents. But the adopted young birds do not. The DNA they inherit from their real parents is not programmed for family responsibility. When they grow up they will obey its instructions to put their children out for adoption.
It is true that certain European members of the cuckoo family place their eggs in the nests of other birds. But as a rule, our lovely North American cuckoos build nests and raise their young chicks with loving care. However, our native cowbird never builds a nest of her own. Like the cuckoo in Europe, she places her eggs in other bird nests and leaves her chicks to be adopted by foster parents.