In trying to explain the existence of the complicated body structures in living things around us, the theory of evolution has been developed. This theory is that all the plants and animals in the world today have developed a natural way from earlier forms that were simpler. According to this theory, men are too, developed from some simpler form, just as the modern one-hoofed horse is the descendant of a small five-toed ancestor.
In trying to prove that evolution did take place, scientists depend on three chief "signs". One of these is the study of fossil remains of animals and plants of past ages. Some of these fossils seem to trace the steps of evolution at work. Fossils of certain crablike animals go back nearly 500,000,000 years and those have shown that fish developed in the waters of the earth before amphibians, amphibians before reptiles, reptiles before birds and so on.
Another "sign" of evolution came from the study of embryology, the growth of a new living thing from an egg. In studying the development of the chick from the hen's egg, there was a time when this embryo was like a fish, later it was like an amphibian, then it passed through the reptile stage and finally into its bird form. The unborn young of all animals go through the same kind of process, repeating their history of development.
The third "sign" is the bodies of living animals. For example, the bone and muscle structure in the paddles of a turtle, the wings of a bird, the flippers of a whale, and the front legs of a horse and the arms of a man are similar in structure. These are some of the "signs" that led to a theory of evolution.
In trying to prove that evolution did take place, scientists depend on three chief "signs". One of these is the study of fossil remains of animals and plants of past ages. Some of these fossils seem to trace the steps of evolution at work. Fossils of certain crablike animals go back nearly 500,000,000 years and those have shown that fish developed in the waters of the earth before amphibians, amphibians before reptiles, reptiles before birds and so on.
Another "sign" of evolution came from the study of embryology, the growth of a new living thing from an egg. In studying the development of the chick from the hen's egg, there was a time when this embryo was like a fish, later it was like an amphibian, then it passed through the reptile stage and finally into its bird form. The unborn young of all animals go through the same kind of process, repeating their history of development.
The third "sign" is the bodies of living animals. For example, the bone and muscle structure in the paddles of a turtle, the wings of a bird, the flippers of a whale, and the front legs of a horse and the arms of a man are similar in structure. These are some of the "signs" that led to a theory of evolution.
