Why does the fossil record not document the series of evolutionary changes during the evolution of animals?

为什么化石记录没有记录动物进化过程中的一系列进化变化？

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They reasoned that while some evolutionary changes involve the loss of genes and are therefore irreversible, others may be the result of genes being switched off.

他们推断，虽然一些进化上的变化涉及基因的丢失，因此是不可逆转的，但其他的变化可能是基因被关闭的结果。

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But not all evolutionary changes make inherent sense.

但不是所有的进化都有内在的意义。

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But successful evolutionary changes continued to form new branches.

VOA: special.2009.02.25

Now these changes, these human evolutionary changes, have created some very interesting metabolic things inside our bodies.

而今,这些改变,这些人类演化造成的变化,在人体内产生了一些很有意思的代谢过程

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The series also covers the evolutionary changes in human life, tracing our development from single cells to highly complex beings.

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If history is any guide, the innards of the next iPhone are likely to represent only evolutionary changes from iPhone 5.

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But Berwick is expected to preside over evolutionary changes whereby the public program becomes less of a rubber-stamp payer and more like an HMO where claims can be rejected.

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