Adaptation refers to a change in the structure or function of an organism that makes it better suited for its environment. Biologists recognize two types of adaptation: plastic adaptation (plasticity) and evolutionary adaptation. Plasticity is the ability of organisms, including humans, to change biologically or behaviorally in response to environmental change. One example of plasticity is human height. It has been shown that over decades, height averages have increased as quality of life has improved. For instance, in 1850, the average height of men in Holland was 5.4 ft (1.6 m), but today their height averages 5 ft 8 in (1.7 m). The increase is due to healthier living brought about by purified drinking water, sewer systems, food regulation, and health care. Evolutionary adaptation involves inherited traits due to genes that pass from generation to generation. An organism's total adaptation to the environment ultimately depends on the combined effect of plasticity and genetic inheritance.
Charles Darwin described the mechanism of adaptation in his book entitled, The Origin of Species, published in 1859. Darwin felt that an organism's adaptation to the environment was a consequence of evolution. He referred to evolution as descent with modification, and explained it by means of natural selection. The theory of natural selection states: more individuals are born than the environment can support; this leads to a struggle for existence in which only a portion of those born in each generation will survive; inherited differences (variations) exist among living things; individuals whose variations better adapt them to the environment survive and have more offspring than less-fit individuals; unequal ability to survive and reproduce gradually leads to a population in which beneficial adaptations accumulate over the generations.
During evolution, the environment interacts with a population's variability. Environmental factors determine which hereditary traits help a population survive and reproduce. Natural selection is the mechanism that explains changes in a population over time as well as the origin of species. Darwin did not know how variations arise in a population, but research has shown that mutations and genetic recombination bring about variations.
Every living thing is a showcase of its adaptations for survival and reproduction. There are endless examples of how inherited traits help adapt an individual to its environment. The arctic fox has white fur that makes it invisible to predators against the snow; the sequoia tree has great height and vast roots that help it compete for sunlight, water, and minerals; the peacock displays its feathers to attract the peahen. Mimicry, where one species looks like another species, is also a good example of adaptive evolution. When a hawkmoth larva, for instance, is disturbed by a predator, it adapts its form to resemble a snake. Mammalian kidneys adapt to different environments. A kangaroo rat, living in the desert, has kidneys with long loops of Henle (structures that take water back into the body). This adaptation results in very concentrated urine. A beaver, on the other hand, spending its time in fresh water, has short loops of Henle. As a result, beaver urine is more dilute. In each case, the length of the loop of Henle adapts the animal to its environment.
This is the complete article, containing 521 words
(approx. 2 pages at 300 words per page).
