阅读36套E15第一篇看不懂，求翻译！

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这一篇看了答案也不懂，主要是文章没读懂，尤其关于fitness那几句搞不懂。
According to natural selection
theory, a worker would enhance her fitness --or ability to
propagate her genes-by hatching her own eggs in addition
to or in place of the queen's. But a typical worker's fitness
would be diminished if other workers' sons, who have   
10    less genetic material in common with the worker,
supplanted the queen's sons (the worker's brothers).