Evolution, Genetics, and Man

Adaptedness and Adaptation . Darwin wrote in 1859: "We see beautiful adaptations everywhere and in every part of the organic world." Indeed, the capacity of life to master even most inhospitable environments is remarkable. During summer months, margins of permanent snow fields in high mountains may acquire a pinkish color, owing to the presence of the alga Sphaerella nivalis. This alga is adapted to live and reproduce at temperatures close to freezing. In contrast to it, some algae inhabit hot springs of Yellowstone Park with temperatures up to 85°C (185°F), which are well above the limit of toleration for most organisms. The emperor penguins inhabit the Antarctic ice, and breed during the long and bitterly cold winters. No nests are constructed; the birds incubate the eggs by placing them on their feet and covering them by a skin fold which they have on the belly. Both sexes and all members of a colony compete for the privilege of incubating the eggs, regardless of whether they are the actual parents.

The universal adaptedness of life to its environment is, next to the nature of life itself, the greatest problem which biology has to face. Darwin has attempted to explain the process of adaptation as an outcome of natural selection impinging upon organic variation. In our present terminology this means that the conservatism of heredity is counterbalanced by the dynamism of mutation and sexual reproduction. Some of the genotypes generated by these processes are adaptive in certain environments, and are perpetuated by natural selection; other genotypes fail to be perpetuated. Some simplest examples of evolutionary adaptation are discussed in the following pages.

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