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Its native mammals are mostly marsupials like kangaroos, bandicoots, and quolls. In the main part of the continent, Australia, 83% of mammals, 89% of reptiles, 90% of fish and insects and 93% of amphibians are endemic. AustralasiaĪustralasia has been separated from other continents for many millions of years. Once it is established, a new species may spread to some places and not others. When new species occur, usually by the splitting of older species, this takes place in one place in the world. This is a topic which fascinated both Charles Darwin and Alfred Russel Wallace. The Proteaceae are a family of flowering plants entirely limited to the southern continents. How these changes have come about is explained by the theory of evolution. They have happened slowly over a long time. So, scientists can see that changes have happened. Climate change and over- hunting by humans are suggested. The causes of this extinction are not yet clear. Horses lived in western Canada until 12,000 years ago, but all horses in North America became extinct about 11,000 years ago. It has teeth which grow all its life, hooves on single toes, great long legs for running, and the animal is big and strong enough to survive in the open plain. Now, however, only one genus exists: the modern horse, Equus. Because grass wears teeth out, horses with longer-lasting teeth had an advantage.įor most of this long period of time, there were a number of horse types ( genera). They ate grass, they grew larger, and they ran faster because they had to escape faster predators. Forests shrank grassland expanded, and horses changed. It was only about as big as a fox.Ībout 30 million years ago the world started to become cooler and drier. This horse lived in woodland, eating leaves, nuts and fruit with its simple teeth. At that time, there were more forests in the world than today. It was a small animal with five toes on the front feet and four on the hind feet. The oldest fossil of a horse is about 52 million years old. The evolution of the horse family ( Equidae) is a good example of the way that evolution works. The ancestors of our horses lived in forests. that is to be expected if the fauna and flora of the earlier strata had gradually evolved into their descendants. The older the strata are.the more different the fossil will be from living representatives. The most convincing evidence for the occurrence of evolution is the discovery of extinct organisms in older geological strata. Also, the later the rocks, the more like the present day are the fossils. Realizing that early fossils were simpler organisms than later fossils.It was Georges Cuvier, the comparative anatomist, who proved that extinction occurred, and that different strata contained different fossils. Realizing that many fossils represented species which do not exist today.This was settled in the 16th and 17th centuries by Conrad Gessner, Nicolaus Steno, Robert Hooke and others. Realizing that things in rocks which looked organic actually were the altered remains of living things.The realization that some rocks contain fossils was a landmark in natural history. The evidence for evolution is given in a number of books. "Nothing in biology makes sense except in the light of evolution". The theory of evolution is the basis of modern biology. There is now "strong quantitative support, by a formal test", for the unity of life. In 2010 an analysis compared sequences to phylogenetic trees, and supported the idea of common descent. At the same time, evolutionary questions are still being actively researched by biologists.Ĭomparison of DNA sequences allows organisms to be grouped by how similar their sequences are. That evolution has taken place is a fact, because it is overwhelmingly supported by many lines of evidence. How has this come about? Evolution has taken place. And the further we go back, the more different the fossils are. So, we know that the animals and plants of today are different from those of long ago. We know that living things have changed over time, because we can see their remains in the rocks. That kind of research is called historical geology. By studying the layers of rock, we can find out about its past. It explains how living things change over a long time, and how they have come to be the way they are.Įarth is very old. The tree of life showing the three domains of life on Earth.Įvolution is a scientific theory used by biologists.