做過托福TPO31第一篇閱讀的同學們一定會對物種形成 (Speciation) 這個生物學概念留下深刻印象，那么我們現(xiàn)在來系統(tǒng)地了解一下什么是物種形成。
一. 物種形成，即從舊物種中分化出來新物種的過程。
(Speciation is the evolutionary process by which reproductively isolated biological populations evolve to become distinct species.)
物種形成主要有四種模式：
異域性物種形成（Allopatric Speciation）
邊域性物種形成（Peripatric Speciation）
臨域性物種形成（Parapatric Speciation）
同域性物種形成（Sympatric Speciation）
二. 異域性物種形成或地理隔離：同一物種，由于如海洋、高山、沙漠等地理隔離，導致分布不連續(xù)，彼此間沒有遺傳基因的交換，漸漸演化為不同的物種。
（Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become vicariant, or isolated from each other to an extent that prevents or interferes with genetic interchange. This can be the result of population dispersal leading to emigration, or by geographical changes such as mountain formation, island formation, or large scale human activities. The vicariant populations then undergo genotypic or phenotypic divergence as: (a) they become subjected to different selective pressures, (b) they independently undergo genetic drift, and (c) different mutations arise in the gene pools of the populations.）
三. 生殖隔離：親緣相近的種群，在自然條件下，不能交配；即使能交配，也不能產(chǎn)生后代，或不能產(chǎn)生可以生育的后代。
（The mechanisms of reproductive isolation are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced are sterile.）
