How Living Things Change (1957)

[Music] How do you think animals like these could change through millions of years into horses? Scientists agree that it happened, but how? Or could you explain how animals that looked like this could develop into elephants, much larger, with long trunks? Can you think of ways prehistoric birds like this could be the ancestors of our modern birds? What caused such changes? How could they occur? What patterns in nature bring about new species of living things or change old ones? A fine dairy herd shows the results of recent changes. Great milk producing cows result from selective breeding. While cows less selectively bred usually give less milk. This change in these living things resulted from breeding only the best milk producers. By selectively breeding chickens, we can get big chickens for meat and other chickens that are less desirable for meat but lay more eggs. Changes brought through selective breeding. Indian corn or maze with small ears and uneven many colored kernels is the original base for our fine modern hybrid corn with its even kernels and full ears. These are examples of changes in living things that have been produced and recorded in a relatively short period of years through careful selection of the parents of succeeding generations. The study of changes in living things that have occurred through millions of years starts with the discovery of records in rock. The finding of remains of plants and animals of the past and the recording of exactly where these fossils were found. From such rock records, we know of animals that lived millions of years ago. And we can see how vast the changes in living things have been when we imagine such flying reptiles as these. But how did living things change? One of the first explanations is associated with the name of Jean Pierre Lamar. He believed acquired characteristics could be passed on to succeeding generations. And on this he based his theory of changes in living things. For example, he would say the long neck of a giraffe was acquired through stretching for food. Stretching lengthened slightly the neck of one giraffe. This acquired characteristic was passed on to its offspring who had longer necks. So Lamar theorized because an early short- necked animal stretched its neck, giraffes have long necks today. He thought the long neck was acquired supposedly. Then if this giraffe doesn't stretch for food but gets it easily or by stooping, it can acquire a bent neck. Then this bent neck will be passed on to its offspring. So we might assume that all future giraffes will have bent necks because this one stooped. Today we no longer accept this theory that acquired characteristics are inherited. For example, these Doberman pincher puppies have long ears and each puppy's ears would be long all his life. But it has been the practice to dock and tape Doberman ears to make them stand erect. Thus, most Dobermans have acquired the characteristic of erect ears. But though this has been true for 50 years or more, the characteristic is not passed on to succeeding generations. Doberman puppies are born with long ears. No, acquired characteristics do not explain the big changes in living things. Sounder explanations of these changes came from Charles Darwin whose theory can be thought of as natural selection. According to Darwin, the basis for changes lies in which animals mate to reproduce. Thus to explain how our modern elephants with long trunks developed from ancient animals with long snouts, Darwin began his theory with selection of breeding stock, natural selection. If among the ancient animals, those with longer snouts bred together, they would tend to produce animals with longer snouts. But why would this kind of mating happen? Darwin theorized that the animals with longer snouts could get more food, so were stronger, lived longer, and naturally produced more offspring. Those with longer and longer snouts or trunks, being more fitted to survive, tended to produce succeeding generations. And so, the modern elephant developed through a long process of natural selection of breeding stock. The fittest to survive lived to reproduce, and long trunks helped make them fit to survive. Animals of various types died out because changing conditions of the earth made them unfit to survive. None of their species had physical traits suited to the new conditions. So we know of them only through stone records. Some specimens of animals had for a time characteristics such as long tusks that helped them survive despite predatory enemies while others without the long tusks died out. So living things changed through breeding as conditions changed. We can see this sort of change in the gradual evolution of the horse from this ancient animal that lived 50 million years ago. It was small, about the size of a sheep. It lived on plants and was food to many predators. Speed in running was its key to survival. So gradually, larger, faster animals were those that reproduced. And as changing conditions required more size and speed, eventually our modern horse developed because the larger, faster animals were naturally selected to reproduce. Hugo de added his own observations of mutations to Darwin's theory. By mutations, he meant the appearance of plants or animals unlike their parents. We can see mutations in mink coloration. This is the natural ranch mink color. But occasionally two mink of this natural color will produce a mutation. Sometimes a mutation that looks like this. A mutation because it is unlike its parents. Many other mutations appear. Light mink, a mutation. very dark mink, another mutation, and even white mink. Each of these colors can be fixed through selective breeding, and a new type of mink can be established very quickly. Thus, mutations can explain apparently sudden changes in living things. In the story of the horse, mutations could explain certain changes. Early horses had four toes. Then three-toed horses appeared. Perhaps a mutation since three toes were an aid to survival. Soon all horses had only three toes. Later horses were probably results of further mutations that aided survival, for they had one main toe with two smaller toes, another mutation. and finally the hoof of our modern horse. Perhaps again a mutation. Thus, natural selection and mutations can explain many of the changes in living things. And as in most science, our understanding is the result of the work of several men. Lamar, whose theory of acquired characteristics, though faulty, helped lead to Darwin, who formulated the doctrine of natural selection. To it, mutations were added by the observations of debris. Through understanding their ideas, we can explain how ancient birds could be the ancestors of modern birds. We can understand how maize could be changed through selective breeding into modern hybrid corn. And we can understand how wide varieties of animals and plants can be developed and new characteristics fixed through the application of our knowledge of how living things change. [Music]