Evolution: The Theory Of Evolution
EVOLUTION : THE THEORY OF EVOLUTION
The French biologist Lamarck proposed, in 1809, a hypothesis to account for the mechanism of evolution, based on two conditions: the use and disuse of parts, and the inheritance of acquired characteristics. So, according to Lamarckism, as the theory came to be known, the long neck and legs of the modern giraffe were the result of generations of short-necked and short-legged ancestors feeding on leaves at progressively higher levels of trees.
In November 1859, Darwin published the Origin of Species by Means of Natural Selection, proposing that natural selection is the mechanism by which new species arise from pre-existing species. The ‘struggle for existence’ described by Darwin was popularised by the coining of the terms such as ‘survival of the fittest’.
MODERN VIEWS ON EVOLUTION
The theory of evolution, as proposed by Darwin and Wallace, has been modified in the light of modern evidence from genetics, molecular biology, palaeontology, ecology, and ethology (the study of behaviour) and is known as neo- Darwinism (neo or new). This may be defined as the theory of organic evolution by the natural selection of inherited characteristics.
Evidence of prehistoric people, such as fossils, tools, and other remains, is rare and often fragmented.
Most scientists believe that human beings and apes, such as chimpanzees and gorillas, share a common ancestor. The ancestors of human beings probably began evolving separately from the ancestors of apes, between about 10 million and 5 million years ago. This evolutionary split marks the beginning of the development of hominids. Hominids are members of the scientific family made up of human beings and early humanlike ancestors. Most anthropologists believe the first hominids were humanlike creatures called australopithecines. The australopithecines first appeared more than 4 million years ago in Africa.
Types of Australopithecines The australopithecines were members of the genus Australopithecus (southern ape). According to differences in the shape of the creatures’ jaws and teeth and the size of their brains, scientists have divided the genus Australopithecus into five species: (1) A. ramidus, (2) A. afarensis, (3) A. africanus, (4) A. robusius, and (5) A. boisei.The most complete australopithecine fossil scientists have found is a partial skeleton of a female A. afarensis. It was found in Ethiopia. This creature, nicknamed “Lucy”, was probably more than 110 centimetres tall and weighed about 30 kilograms. By about 2.5 million years ago, A. africanus replaced A. afarensis. Many scientists believe that an evolutionary split occurred among the australopithecines during the time of A. africanus. This split resulted in the appearance of an additional evolutionary line, separate from A. africanus, that led to A. robustus and A. boisei. Scientists refer to these two species as the robust australopithecines.
The First Human Beings
Most anthropologists believe that the first human beings evolved from a gracile australopithecine about 2 million years ago. Homo habilis is considered by anthropologists to be the oldest human species. These prehistoric people lived in Africa about 2 million years ago. Homo erectus: Fossil evidenceindicates that about 1.5 million years ago Homo habilis had evolved into a more advanced human species. Scientists call this species Homo erectus.
Early Homo Sapiens Between 400,000 and 300,000 years ago, Homo erectus evolved into a new human species called Homo sapiens. The term Homo sapiens means ‘wise human being’. All people living today belong to this species. But early Homo sapiens differed greatly from modern people. Early Homo sapiens were about as tall as modern human beings. Neanderthals were a type of early Homo sapiens who lived in parts of Europe and the Middle East about 130,000- 35,000 years ago. Neanderthals have become the most widely known of the early Homo sapiens mainly because they were the first prehistoric people to be discovered.
Rise of Modern Human Beings
The first prehistoric people with modern human features appeared about 100,000 years ago in either the Middle East or Africa. These people had a chin, a high forehead, and a smaller, less-protruding face than the earlier Homo sapiens had.