Final answer:
Chimpanzees are the closest living relatives to humans on a phylogenetic tree, followed by gorillas, orangutans, and much less closely, dolphins. Over 98% genetic similarity between humans and chimpanzees indicates a recent common ancestor. Phylogenetic trees reflect these evolutionary relationships.
Step-by-step explanation:
Among the animals listed - chimpanzees, gorillas, orangutans, and dolphins - chimpanzees are the closest to humans on a phylogenetic tree. Humans and chimpanzees belong to the biological family Hominidae, which includes only four living genera: humans, chimpanzees, gorillas, and orangutans. These are part of a group known as the Great Apes, which also includes the bonobo, a close relative of the chimpanzee. The genetic similarity between humans and chimpanzees is over 98%, which indicates they share a more recent common ancestor with us than gorillas or orangutans do.
Gorillas and humans also share more than 97% of their DNA, but the similarity is slightly less than that with chimpanzees. Orangutans, while still closely related, are more distantly related to humans than gorillas and chimpanzees. Dolphins, although intelligent mammals, are not primates and are not closely related to humans on the evolutionary scale. They belong to a different order of mammals, the Cetaceans, which are more closely related to even-toed ungulates like hippos.
Therefore, when examining a phylogenetic tree, we find that the closest relatives to humans are chimpanzees, followed by gorillas, then orangutans, with dolphins being much less closely related. This closeness on the phylogenetic tree indicates a more recent common ancestor and reflects significant genetic and behavioral similarities. Phylogenetic trees and genetic studies have greatly helped in understanding these evolutionary relationships.