It's a mechanism that they have evolved in order to prevent foreign genes from entering a cell and being expressed.

它们进化出这种机制来,防止异源基因进入细胞并表达

耶鲁公开课 - 生物医学工程探索课程节选

And they do that to localize the source of the problem.

他们会不断的减小,寻找空间来定位问题源。

麻省理工公开课 - 计算机科学及编程导论课程节选