retreat(1) (iou) and natural selection (sh)

retreat(1) (iou)

retreat noun. ME.
[Old French retret (masc.), retrete (fem.), vars. of retrait(e) use as noun of pa. pple of Old & mod. French retraire from Latin retrahere RETRACT verb1.]
A backhanded blow. rare. Only in ME.
Military. The signal to withdraw from battle etc. (chiefly in blow the retreat, sound the retreat, blow a retreat, sound a retreat). Now also, a bugle call followed by drumming at sunset; a flag-lowering ceremony including this. LME.
b. The recall of a pursuing force. Only in L16.
The action or an act of retiring or withdrawing in the face of opposition, difficulty, or danger, esp. on the part of an army, combatant, etc., after defeat or to avoid an engagement. Now also, (a) decline in the value of shares etc. LME.
beat a retreat: see BEAT verb1 17.
M. R. D. Foot To harass the..German retreat by..ambushing. J. Archer The dollar was on the retreat. Time The intruders were in retreat. S. Rushdie There can be no retreat from the truth.
b. The action of receding or sloping back, recession. L18.
F. J. Monkhouse The retreat of the continental ice-sheet.
A place of seclusion, privacy, or contemplation; a retired place or residence, spec. a second or further Home. Also, a place of refuge; a hiding place, a lair, a den. LME.
Henry Miller A cosy retreat in which everything is offered you gratis. R. L. Fox A peaceful retreat of grottoes and shaded walks.
b. An establishment or institution for the care of the mentally ill, the elderly, etc. L18.
The action of retiring into privacy or Security; withdrawal from public life, office, etc.; retirement, seclusion. L15.
J. Updike Physical frailty compelled retreat from social excitements.
b. (A period of) complete seclusion for religious observance and contemplation. M18.
Architecture. Recessed work; a recess or recessed part in a wall etc. L17.

natural selection (sh)

Process that results in adaptation of an organism to its environment by means of selectively reproducing changes in its genotype.

Variations that increase an organism's chances of survival and procreation are preserved and multiplied from generation to generation at the expense of less advantageous variations. As proposed by Charles Darwin, natural selection is the mechanism by which evolution occurs. It may arise from differences in survival, fertility, rate of development, mating Success, or any Other aspect of the life cycle. Mutation, gene flow, and genetic drift, all of which are random processes, also alter gene abundance. Natural selection moderates the effects of these processes because it multiplies the incidence of beneficial mutations over generations and eliminates harmful ones, since the organisms that carry them leave few or no descendants. See also selection.

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