Evolutionary trees are used to represent the relationships between organisms. Branches show places where speciation has occurred, and a new species has evolved.
In this evolutionary tree, species A and B share a recent common ancestor. Species A is therefore most similar to species B.
Species F and G also share a recent, common ancestor, however this common ancestor is different to the common ancestor of A and B. The common ancestor of F and G shared a common ancestor with species E. All seven species share a common ancestor at the bottom of the tree, probably from the distant past.
The information is collected from a variety of sources such as fossil records and DNA sequences. The more varied the evidence collected, the more likely the scientists are to be correct in their decisions about how closely related different organisms are.
In the evolutionary tree above, which two species were formed by only two speciation events?
A and B were formed by two speciation events. Following the tree from the bottom there are two branch points as we move up to A and B. Each branch point is a speciation event.
In the evolutionary tree above, which species is likely to look most like species C?
Species D is most likely to look like species C as they are the most closely related species on the evolutionary tree. They share a common ancestor that other species do not share.