Is it possible that 2 organisms could be equally related to humans, but not equally related to each other?
It is possible to have two or more organisms that may be equally shown to be related to the human species, but not equally related to each other. The use of phylogenetic trees arranges organisms by shared traits or the development of a particular behavior, such as dwelling in trees as opposed to dwelling on the ground. I answered a question on phylogenetics a short while ago, which showed two divergent lines of ape-like mammals, and the deciding factor between the two was the existence of a tail, a prehensile grasping appendage which would make the mammal suitable for tree dwelling. All the old-world monkeys, the macaques, were in this line, while humans, gorillas, chimpanzees, and orangutans were in another, possessing no tail, making them more suitable for living on the ground. In this second lineage, gorillas and chimpanzees are linked together with humans, but are very different from each other, in both physical and mental capability.