Similarly, a plant or animal cannot squander all its energy on growing a big body if none would be left over for reproduction, for this is the surest way to extinction.

同样，如果一种植物或动物没有留下任何可以繁殖的后代，它就不能把所有的能量浪费在使自己变得更强壮上，因为这是最可能走向灭绝的方式。

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Because natural selection favors reproduction over health, biology evolves more slowly than culture, and pathogens evolve more quickly than humans.

因为自然选择比起健康而言更喜欢繁殖，生物的演化远不及的微生物的繁殖，病原体的进化远远快于人类。

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"Survival doesn't always take precedence over reproduction," Ms Greenhalgh said.

“存活不总是优先于繁殖，”Greenhalgh女士说。

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In practice, the embryos used in the collection of stem cells were left over from attempts to assist reproduction -- donated by couples who used in vitro fertilization.

CNN: Looking for middle ground in a minefield