For example, Darwin observed a population of giant tortoises in the Galápagos Archipelago to have longer necks than those that lived on other islands with dry lowlands. These tortoises were “selected” because they could reach more leaves and access more food than those with short necks.

Tortoises occurring on more arid islands had to stretch their necks to reach branches of cactus and other vegetation. Consequently, these later individuals had longer necks and a high peak to the front edges of their shells, which enabled them to stretch their heads almost vertically.

Giant Tortoises Darwin noticed that different tortoise species lived on islands with different environments. He realized that the tortoises had traits that allowed them to live in their particular environments. For example, tortoises that ate plants near the ground had rounded shells and shorter necks.

Tortoises from Pinzn Island (formerly Duncan Island) are “saddle-backed,” meaning that their shells rise in the front, like a saddle. This adaptation makes it easier for them to lift their necks and feed on taller cactus. Tortoises from Santa Cruz (formerly Indefatigable Island) have “dome-shaped” shells.

13 species

Neo-Darwinism has failed as an evolutionary theory that can explain the origin of species, understood as organisms of distinctive form and behaviour. In other words, it is not an adequate theory of evolution.

The problem with the theory of evolution by natural selection, according to Nagel, is that it does not provide an understanding of consciousness as a likely product of evolution.

The main consequence of negative selection is the extinction of less-adapted variants. If the best-adapted variant does not change because it is at a stable local optimum, then negative selection will remove all new variants for that optimal trait.

Neo-Darwinism is generally used to describe any integration of Charles Darwin’s theory of evolution by natural selection with Gregor Mendel’s theory of genetics. The term “Neo-Darwinism” marks the combination of natural selection and genetics, as has been variously modified since it was first proposed.

Survival of the fittest, term made famous in the fifth edition (published in 1869) of On the Origin of Species by British naturalist Charles Darwin, which suggested that organisms best adjusted to their environment are the most successful in surviving and reproducing.