The evolution of the whale
The evolution of the whale
The blue whale is the largest animal that has ever lived on earth. It looks like a giant fish, but if we look at it closely, it does not seem to fit in among the other fish. And it behaves rather differently. A whale needs to swim to the surface to breathe. Because, just like the mammals on land, the whale breathes air, which it inhales into its lungs.
Fish do not have lungs. Instead they breathe with gills. And the whale gives birth to living young who drink its mother’s milk, they suckle, just like mammals on land. Fish don’t suckle. The whale has a steady body temperature of about 37 degrees celsius, just like the mammals on land.
Fish change their body temperature depending on the surroundings. So, it seems like the whale is a mammal! If so, there are mammals both on land and in water! Is this possible? Have mammals evolved twice during evolution, in two different environments?
Or have they only evolved once, and then spread to different environments? How can we find that out? We state two hypotheses: One: Mammals have evolved twice during evolution, once on land and once in water. In this case the whale is closely related to fish, even though it is in many ways similar to the mammals on land. Hypothesis two: Mammals have evolved once, and then spread both on land and in water.
In this case the whale is closely related to land dwelling mammals, even though it is in many ways similar to the fish in the water. When a species develops during evolution, it happens gradually, in many small steps. If whales have evolved from fishes, there must have been a few species along the way, part fish and part whale. Creatures that perhaps had a mixture of gills and lungs. Are there any traces of such species?
No, not one single trace. Are there any traces of any intermediates of whales and land living mammals? Yes, in fact there are! These are remains of an animal that lived millions of years ago and which is now preserved in the bedrock. It is the fossil of a maiacetus.
Look at the skeleton. Compare it to the skeleton of a land dwelling mammal, for instance a cat. The skeletons are rather similar, but the front and the back legs are shorter in the maiacetus. Now compare with the whale’s skeleton. The whale has front legs, that are even shorter than those of the maiacetus.
The back legs have become very small, and they are no longer connected to the spine, but they are clearly visible. And there are more fossils which are intermediates in the evolution from mammals on land to mammals in the ocean, whales. Fossils in the bedrock give a picture of the path of evolution, and the gradual change of species. There are more ways of exploring the evolution of the whale. We can study the DNA of the animals.
Two individuals who are closely related have many genes in common. The more remotely they are related, the more different are the genes. Whales and fish have genes which are very different. Whales and land dwelling mammals, on the other hand, have lots of genes in common, so they are much more closely related. The whale’s closest relative on land is the hippopotamus.
Even though whales and hippopotami look so different, a large proportion of their genes are similar. This is why we know that they are more closely related than we might think when we look at them. So, when we compare how the animals appear, their anatomy, and their characteristics and when we look at fossils and when we compare the DNA of the animals we can see that it is our second hypothesis that is correct. Whales have evolved from mammals that once lived on land. And all these observations of the evolution of the whale fit with what we know about the development of species.
They support the theory of evolution.