In 1831, Charles Darwin (1809-1882), when only twenty-two, as a naturalist was part of the scientific expedition on board the brig ofthe British navy H. M. S. Beagle, who made an expedition of five years (1831-1836), going around the world with the main purpose of mapping the coast of South America. Darwin was able to study and collect extensive data, and collected and researched many living things never seen by him. Then, properly prepared, sent to Londonfor further study, to which he devoted the rest of his life.
Darwin knew the theory of Lamarck, but found no evidence in his observations of it. In the Galapagos Islands found many species of finches that differ from each other by small variations of a common feature.
He also devoted much time to admire the giant tortoises. He found that on each island lived a different species of turtle. All these species were differentiated mainly by the shape of the shell.
Darwin thought that all the islands finches descended from a common ancestor and that, over time, had grown up living species.The same should have happened with the turtles. The small differences between them and other species of turtles and fincheswould have appeared very slowly, over hundreds or thousands of years.
Darwin knew his theory of evolution would be very controversial, so he spent many years collecting data and preparing his book, whichexplained in detail.
Alfred Russell Wallace (1823-1913), British and also younger thanDarwin, traveled the world in search of birds and butterflies tomuseums and private collections. He was in the Amazon, Southeast Asia and Australia, and there he began to sense the process which produced the evolution.
When he was clear about the process of natural selection, wrote a letter to a renowned naturalist, none other than Charles Darwin. Upon receipt of this letter, Darwin advanced the presentation of its own conclusions, to act jointly with Wallace.
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Darwin and Wallace shared their findings and presented to the Linnean Society of London in 1858. A year later, Darwin published his Origin of species by natural selection, in which he explained his theory to support it on numerous observations of nature.
The theory of evolution or Darwinism is based on the followingpoints or postulates:
1.The life forms are not static but evolve, species are continually changing, some others originate and become extinct.
2.The process of evolution is gradual, slow and continuous, notdiscontinuous leaps or sudden changes.
3.The like organisms are related and descended from a common ancestor. All living organisms can be traced to a single origin of life.
4.La natural selection is the key in two phases, which explains the whole system. The first phase is the production of variability: the generation of spontaneous in individuals. The second selection through survival in the struggle for life: thefittest individuals, those born with spontaneous favorablemodifications to address the environment will be more likely tosurvive, to reproduce and leave offspring with these advantages.
How Darwin and Wallace explain why giraffes have the neck and legs so long?
At first there would be a population of antelope neck and legs ofnormal length. Some, who had the neck and legs somewhat longer,may feed on acacia leaves, which would help them survive better in periods of drought. Served natural selection, which allowed the fittest, the highest, reproduce. Among the descendants abound overthe tall and, again, natural selection would select the highest among them, for the lowest were more likely to die of starvation before they become adults. Thus, as reproduced in each generation higher animals, each time the offspring were higher. A few million years, allanimals were high, as the current giraffes.
1. In a population of giraffes individuals have variations. So there will be some individuals with neck and legs longer than others.
2. In bad times, as long periods of drought, giraffes neck and long legs can reach the leaves of the upper branches of acacia trees to eat, so it will be more likely to survive and reproduce. The otherwould perish of hunger.
3. Generation after generation, continuously and gradually, thepopulation will be more abundant giraffes legs and long neck.