Biological Evolution Changes over Billions of Years

Long before the mechanisms of biological evolution were understood, some people realized that organisms had changed over time and that living organisms had evolved from organisms that were no longer alive on Earth. In the 1760s, the French naturalist Count George-Louis Leclerc de Buffon (1707-1788) wrote his Natural History of Animals, which contained a clear statement of the possibility of evolution. Buffon observed that the limb bones of all mammals were remarkably similar in many details (Figure 1.2). He also noticed that the legs of certain mammals, such as pigs, have toes that never touch the ground and appear to be of no use. He found it difficult to explain the presence of these seemingly useless small toes by the commonly held belief that Earth and all its creatures had been divinely created in their current forms relatively recently. To explain these observations, Buffon suggested that the limb bones of mammals might all have been inherited from a common ancestor, and that pigs might have functionless toes because they inherited them from ancestors that had fully formed and functional toes.

Human arm Dog foreleg Seal flipper

Human arm Dog foreleg Seal flipper

Mammalian Forelimbs

1.2 All Mammals Have Similar Limbs Mammalian forelimbs have different purposes: Humans use theirs for manipulating objects, dogs use theirs for walking, and seals use theirs for swimming. But the numbers and types of their bones are similar, indicating that they have been modified over time from the forelimbs of a common ancestor.

1.2 All Mammals Have Similar Limbs Mammalian forelimbs have different purposes: Humans use theirs for manipulating objects, dogs use theirs for walking, and seals use theirs for swimming. But the numbers and types of their bones are similar, indicating that they have been modified over time from the forelimbs of a common ancestor.

Buffon did not attempt to explain how such changes took place, but his student Jean-Baptiste de Lamarck (1744-1829) proposed a mechanism for such changes. Lamarck suggested that a lineage of organisms could change gradually over many generations as offspring inherited structures that had become larger and more highly developed as a result of continued use or, conversely, had become smaller and less developed as a result of lack of use. Today scientists do not believe that evolutionary changes are produced by this mechanism. But Lamarck had made an important effort to explain how living things change over time.

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