Similarly, the earth can exist as a biosphere precisely because of the diversity of organisms it contains. Animals are not capable of photosynthesis and would not survive if there weren't plants to trap the energy of sunlight. The human species is no different, and this alone is enough to raise serious questions about any effort to rank one human or group of humans against another. It is meaningless to ask whether one lymphocyte is better than another, or whether blood cells are better than nerve cells. Each is essential for the success of the others, and for the success of the larger whole.
Diversity is of even greater importance for the origin of successful biological systems.
The reason we exist in our current forms is that, over a long period of time, variants of the ancestors of humans, and before that, variants of the ancestors of the ancestors were produced. Natural selection acted on the pool of variationto yield what we now see as human beings, and the same is true of lions, wolves, maples, and piranha. Natural selection isn't interested in producing a perfect lion, maple, piranha or human being. Rather, the biological process aims to produce variants. This is the only way to be prepared for unknown challenges, times when the environment, the reality which selection reflects, changes in unpredictable ways.