An important challenge to traditional (pre-1860) ideas about species was the observation that seemingly dissimilar organisms such as hummingbirds, humans, and whales have similar skeletal structures. This most directly suggested to biologists that .

Dissimilar organisms might have evolved from a distant, common ancestor.

Explanation:

First of all we should know species. Species is considered as a basic unit of taxonomic classification of an organism.

Initially, the scientists are agreed on this phenomenon that all distinct species are evolved gradually from common ancestor. Today, the species which are different from each other just like hummingbirds, humans and whales are from the same ancestor but with the time passage genetic mutation occurs and at the end dissimilar organisms we can see in our environment/surroundings.