张教授表示，在我们的祖先开始看到颜色后，一种对信息素信号通路十分重要的基因遭受了有害变异，使气味信号不能到达大脑。
After our ancestors began to see color, a gene important in the pheromone-signaling pathway suffered a deleterious mutation, making it impossible for the scent signals to reach the brain, Zhang said.
有一些变异不改变“单词”，即基因；有一些会改变单词但不会改变它的意思；而有一些变异则会改变单词的含义，产生有利或有害的后果。
Some do not change the "words" that are the genes; some change a word but not its meaning; and some change the meaning in a way that can be beneficial or harmful.
许多轻度的有益变异会随机丢失，而轻度有害的变异则会传播开来并在人群中固定下来。
Many slightly beneficial mutations can be lost by chance, while mildly deleterious ones can spread and become fixed in a population.
许多轻度的有益变异会随机丢失，而轻度有害的变异则会传播开来并在人群中固定下来。
Many slightly beneficial mutations can be lost by chance, while mildly deleterious ones can spread and become fixed in a population.
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