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venom
Venom is a form of toxin secreted by an animal for the purpose of causing harm to another. Venom is injected into victims by means of a bite, sting or other sharp body feature,〔(【引用サイトリンク】title=venom - Definition from the Merriam-Webster Online Dictionary )〕 which differentiates it from poison (that is absorbed, consumed or inhaled).
The potency of different venoms varies; lethal venoms are often characterised by the median lethal dose (LD50, LD50, or LD-50), expressed in terms of mass fraction (''e.g.'', milligrams of toxin per kilogram of body mass), that will kill 50% of the target of a specified type (''e.g.'', laboratory mice).
Utilization of venom across a large number of species demonstrates an example of convergent evolution and a homoplastic trait. It is difficult to conclude exactly how this trait came to be so intensely widespread and diversified. The multigene families that encode the toxins of venomous animals are actively selected on, creating more diverse toxins with specific functions. Venoms adapt to their environment and victims and accordingly evolve to become maximally efficient on a predator’s particular prey (particularly the precise ion channels within the prey). Consequently, venoms become specialized to an animal’s standard diet.
Venomous animals resulted in 57,000 human deaths in 2013, down from 76,000 deaths in 1990.
==Diversity==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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