The second mechanism is a more gradual process of adaptive mutation, whereby the capability of the virus to bind to human cells increases during subsequent infections of humans.

第二种机制是一个渐进的适应性变异过程，在这一过程中，伴随人类受到感染，病毒与人体细胞相结合的能力增加了。

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Each additional human case increases opportunities for the virus to improve its transmissibility, through either adaptive mutation or reassortment.

每增加一例人间病例增强了该病毒通过适应性突变或重组提高其可传播性的机会。

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Scientists have discovered a group of people in Ecuador with a rare gene mutation that could reveal ways to extend the human life span.

科学家在一群厄瓜多尔人身上发现了一种罕见的基因突变，有望据此揭开长寿的谜底。

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Furthermore, a human mutation leading to IRAK4-deficient individuals has been well characterized.

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It could also, however, be a mutation of another human coronavirus.

FORBES: Magazine Article

Instead, they argued, a fortuitous mutation in the human brain may have triggered an explosion in human creativity 50, 000 years ago, leading to a sudden appearance of personal ornaments, skilfully-crafted art, novel tools and weapons.

BBC: NEWS | Science/Nature | Study reveals 'oldest jewellery'