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小编为托福考生们准备了托福阅读
TPO31
原文
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各位考生们在
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Speciation in
Geographically Isolated Populations
Evolutionary
biologists believe that speciation,the formation
of a new
species, often begins whensome kind of
physical barrier arises and divides
apopulation of
a single species into separatesubpopulations.
Physical separation
between subpopulations
promotes the formation of newspecies because once
the
members of one subpopulation can no
longer mate with members ofanother
subpopulation,
they cannot exchange variant genes that arise in
one of
thesubpopulations. In the absences of
gene flow between the subpopulations,
genetic
differencesbetween the groups begin to accumulate.
Eventually the
subpopulations become sogenetically
distinct that they cannot interbreed even if
the
physical barriers between themwere removed. At
this point the subpopulations
have evolved
into distinct species. This routeto speciation is
known as
allopatry (
“
alio-
”
means
“
< br>different
”
，
and
“
patria
”
means
“
homeland
”
).
进化生物学家认为物种形成
(
也就是新物种的产生
)
经常是某种物理障碍<
/p>
(
地理隔离
)
的
出现
把一个单一物种群分为隔离的亚种群。亚种群的身体隔离促进了新物种的产生，因为
一旦亚种
群中的成员无法与其他亚种群中的成员交配，那么亚种群之间就没有变种基因的
交换。缺乏了
基因交流，亚种群之间的遗传差异就开始变大。最终这些亚种群的基因差异
变得十分明显，以
至于它们无法进行种族内的交配，即使它们之间的物理障碍已经消除。
这时，这些亚种族就演
化成了独立的物种。
这样的物种形成的方
式被称作异域性
(
“
alio-
”
意思是
“不同的”
,
“
patria
”
< br>意为“故乡”
)
。
Allopatric speciation may be the main
speciation route. This should not be
surprising,since allopatry is pretty
common. In general, the subpopulations of
most species areseparated from each
other by some measurable distance. So even
under normal situationsthe gene flow
among the subpopulations is more of an
intermittent
trickle than a steadystream. In addition, barriers
can rapidly
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