Chimpanzees and gorillas more closely resemble each other anatomically than either resembles humans. For example, the hands of chimpanzees and gorillas are structurally similar and quite different from human hands. Genetic-distance data suggest, however, that humans and chimpanzees are more closely related to each other than either is to gorillas. Assuming that the genetic-distance data are correct, give two explanations for the observed anatomical similarity between chimpanzees and gorillas.
The anatomical structures of organs are generally closely related to the function they serve. For example, the morphology of the hands of chimpanzees and gorillas are more similar to each other than either is to humans’, since they are both knuckle-walking species, while human beings are bipedal. As a result, to explain the anatomical similarities between chimpanzees and gorillas with knowing that humans and chimpanzees are actually more closely related to each other, we may need to reconstruct the phylogenetic relationships among these three species, which has mainly two possibilities.
One possibility is that the common ancestor of humans, chimpanzees, and gorillas was a knuckle walker, and this locomotion was preserved in chimpanzees and gorillas, with human bipedal locomotion evolved from knuckle walking at a later stage. This is to say, the structural similarity between chimpanzees and gorillas is due to homology, with these characteristics descended from a common ancestor, and the differences in morphology of human beings are related to our derived characteristics.
Another possible explanation is that the common ancestor of all three species was not a knuckle walker. Instead, knuckle walking has evolved twice, independently in gorillas and chimpanzees, as the result of convergent evolution. Therefore, the structural similarity between chimpanzees and gorillas is due to analogy, with similar structures being “favored” by natural selection in these two species to solve similar adaptational problems. Humans are different from them because we have separately evolved bipedal locomotion, with a different strategy being “favored” by natural selection.
Comments