Gradualism
The gradualism is a concept of evolutionary theory . It has two different meanings. In the context of the evolution rate, gradualism means that the evolution rate is constant (phyletic gradualism). In the context of the evolution of adaptations , gradualism means that adaptations are formed over many intermediate steps and do not appear erratic.
Phyletic gradualism is when the rate of evolution is constant. If the rate of evolution within a species is slower than when new species emerge, it is called punctualism instead . While the Darwinian theory of evolution is not dependent on phyletic gradualism, in connection with the evolution of adaptations, gradualism is a component without an alternative.
Darwin always emphasized that evolution is slow and gradual. Stephen Jay Gould concluded that Darwin meant phyletic gradualism and that the theory of punctualism contradicted Darwinism and neo-Darwinism . According to Richard Dawkins , Darwin did not refer to the rate of evolution and speciation . Darwin's remarks in the latter context are entirely compatible with punctualism:
“Many species never experience further changes when they are formed (...) and the periods during which the species are subject to modification were long, measured in years, but probably in relation to those in which they remained unchanged are, but only briefly. "
Darwin and all subsequent versions of Darwinism were gradualistic in terms of the evolution of adaptations but not in terms of the rate of evolution. The only condition that the theory of evolution places on the rate of evolution is that fossils must not evolve faster than the fastest experimentally proven evolution rates based on normal genetic variation. Failure to meet this condition would pose a serious challenge to neo-Darwinism. However, all fossil evolution rates known to date are slower than those from genetic experiments.
Individual evidence
- ↑ a b c d Matt Ridley : Evolution . John Wiley & Sons, 2003 (3rd edition). ISBN 1405103450 .