The Evolution of the Birds

Abstract

The evolution of the birds is far from being understood. The new fossil findings in China have only added to the controversy. Monkeys have had an arboreal life, jumping down from trees, for 45 million years, without having acquired wings or wing rudiments. Actually flight did emerge in the mammals but in a quite different group--the bats. Flight appears during evolution as a periodic phenomenon. It emerged for the first time in insects, the second time in pterosaurs (flying reptiles), later in birds and finally in bats. Some fishes are also able to fly. Of importance is that these animal groups are not directly related. During evolution flight came and disappeared without previous announcement. Until recently, the flight of an insect was considered to be, at best, analogous to that of a bird, but at present genetic analysis reveals that the same genes are responsible for the flight in invertebrates and vertebrates, the wing of an insect is determined by the same type of genes that decide the formation of the wing of a bird. By genetic manipulation, flies that normally have two wings, can be produced with four wings and birds can also be obtained in the laboratory with four wings. Evolution is usually assumed to be connected with progress and increased perfection, however it did not follow this pass in birds. The avian body lacks several organs that are vital to other animal groups.