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In population genetics, directional selection is a type of natural selection in which one extreme phenotype is favored over both the other extreme and moderate phenotypes. This genetic selection causes the allele frequency to shift toward the chosen extreme over time as allele ratios change from generation to generation.
The uncinate fasciculus is a bi-directional pathway between the temporal lobe and frontal lobe; it is traditionally considered to be part of the limbic system. [2] It has been proposed that the uncinate fasciculus allows mnemonic representations stored in the temporal lobe to interact with and guide decision making in the frontal lobe. [4]
The peacock tail in flight, the classic example of an ornament assumed to be a Fisherian runaway. Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of ostentatious male ornamentation by persistent, directional female choice.
Mutation and selection. The concept of sexual selection was introduced by Charles Darwin as an element of his theory of natural selection. [1] Sexual selection is a biological way one sex chooses a mate for the best reproductive success.
The two-streams hypothesis is a model of the neural processing of vision as well as hearing. [1] The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual systems. [2] Recently there seems to be evidence of two distinct auditory systems as well.
The discipline of anatomy can be subdivided into a number of branches, including gross or macroscopic anatomy and microscopic anatomy. [10] Gross anatomy is the study of structures large enough to be seen with the naked eye, and also includes superficial anatomy or surface anatomy, the study by sight of the external body features.
However, current evidence in the fossil record supports the concept of mass extinctions. As a result, the general idea of catastrophism has re-emerged as a valid hypothesis for at least some of the rapid changes in life forms that appear in the fossil records. A very large number of fossils have now been discovered and identified.
For improved clarity, the directional term palmar (from Latin palma 'palm of the hand') is commonly used to describe the front of the hand, and dorsal is the back of the hand. For example, the top of a dog 's paw is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface.