Natural Selection:
Evolution produces several important patterns:
I. Divergence from common ancestors
Divergence can also occur (perhaps more commonly!) if an ancestral population is divided into two or more by changes in geography: because natural selection works by chance survivals, it is unlikely that exactly the same variations of the ancestral population will survival in the two or more separated populations. Over time, if the populations meet again, the accumulation of variations may be significant enough that they are distinct species.
II. Trends:
Ancestor and descendants form a lineage (historical line). If the same basic adaptations are selected for and elaborated over time, this is called a trend. (e.g., longer and longer legs for fast running; longer and longer necks for browsing in trees, etc.)
III. Adaptive radiations:
If a new adaptation (or loss of competitor group) occurs, many different variations from a common ancestral population might survive (new or unoccupied “niches” in environment). Over a geologically short period time, a common ancestor can radiate into many different descendant lineages.
IV. Convergence from different ancestors
V. Living fossils: Populations little changed over long periods of geologic time.
VI. Heterochrony:
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