In most cases, the genetic dissimilarity between the two hosts is too great.

多数情况下，两个宿主间的 遗传基因差异太大。

To the wingless a more arresting phenomenon is their dissimilarity in every particular except shape and size.

对于没有翅膀的人类来说，一个更加饶有趣味的现象，却是这两个了形状大小之外，在每一个面都截然不同。