Primatların ortaya çıxışıAlıntı
Primates first appeared just under 65 million years ago, after the age of the dinosaurs. The early primates lived in tropical rain forests. They were arboreal and had grasping hands and feet. As they evolved, primates became better-adapted to life up in the trees, developing binocular vision to enable them to judge distance with great accuracy. Today, there are more than 400 species of living primates, the majority of which are still most at home in the trees, but some species, including humans, now live on the ground.
Sayfa 37
Darwin knew that evolution could work only if there was inheritance. He could not have had a knowledge of modern genetics, but during the 20th century, it became clear that the genetic code he sought was contained in the chromosomes inside the nucleus of almost every cell of every living organism. Each human cell contains 20,000–25,000 genes, each of which has coded instructions for specific characteristics. The code is mainly in the form of a molecule of DNA, which includes four chemicals, called bases, arranged in pairs. Every gene is encoded by a specific sequence of base pairs.
Sayfa 36
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What is a species?Alıntı
A common, working definition of a species is that it’s a discrete population of organisms that doesn’t naturally interbreed with other groups. By this definition, there are probably more than 10 million species on Earth today, including about 5,000 mammals, of which about 435 are primates. However, every individual within a species is different, and genomes evolve over time. How different can an individual or group be before it should be considered a separate species Members of different species can still interbreed if they are not yet too genetically distinct. Some species interbreed only under human control; for example, a mule or hinny is the offspring of a horse and a donkey but is sterile. However, other species interbreed successfully in the wild, and we now know that our species Homo sapiens did so with Neanderthals and other archaic human species.
Sayfa 37