Darwin Encyclopedia Articles

Ancestral ranges and historical biogeography The Earth's biodiversity is not distributed evenly across its surface. To understand biogeographic patterns, it is necessary not only to consider current conditions (of climate, ecology, etc.), but also to view them in their historical context, as outcomes of both biotic (for example, speciation or adaptation) and abiotic (for example, geological) evolutionary processes. The field of historical biogeography is grounded in... Macroevolution Large-scale patterns and processes in the history of life, including the origins of novel organismal designs, evolutionary trends, adaptive radiations, and extinctions. Macroevolutionary research is based on phylogeny, the history of common descent among species. The formation of species and branching of evolutionary lineages mark the interface between macroevolution and microevolution, which addresses the dynamics of genetic variation within populations. The term macroevolution was used by the geneticist Richard Goldschmidt around... Organic evolution Organic, or biological, evolution is the modification of living organisms during their descent, generation by generation, from common ancestors. It is to be distinguished from other phenomena to which the term evolution is often applied, such as chemical evolution, cultural evolution, or the origin of life from nonliving matter. Organic evolution includes two major processes... Punctuated equilibria (evolutionary theory) The term "punctuated equilibria" refers to Stephen Jay Gould and Niles Eldredge's 1972 proposal regarding the nature of biological data as preserved in the fossil record and the implications that those data have for evolutionary theory. Eldredge and Gould proposed that the history of life was not characterized by... Species concept The idea that the diversity of nature is divisible into a finite number of definable species. In general, species concepts grow out of attempts to understand the very nature of biological organization above the level of the individual organism. There are two basic questions: (1) What does it mean to be a species in general? Do all species have certain characteristics, such as... Species stability Darwin's On the Origin of Species linked processes observable in the present to patterns in the fossil record and formulated a coherent theory of evolution by natural selection. That link has been challenged by paleontologists on the grounds that the fossil record actually demonstrates long periods of little change in lineages interspersed with brief periods of... Articles courtesy of Access Science http://www.AccessScience.com Copyright McGraw-Hill, all rights reserved. Back Spotlight Home Page