Homo Sapiens Sapiens, 200,000 years old at least. In that time, our brows have receded, our chins have become less pronounced, and depending on the geographical region in which Humans have settled, they have gained numerous adaptations.
Among these are, almond Asiatic eyes with the double lid to deal with the colder temperatures and desert sands of central Asia, pale skin and light hair in northern areas along with an elongated nose that helps with temperature regulation and aides smelling. Extra body hair in some areas, little body hair in others to aid temperature regulation. Hair that grows straight, rather than curly, light colored eyes, and the list goes on.
All of these are regional adaptations to local environments that took place over the last two hundred thousand years. The time it takes for new species to form is measured in generations, thousands of generations.
Aside from that, the basic shape of all fish, mammals, and reptiles, has been consistent for millions and millions of years, and that is unlikely to change. That is, two arms, two legs, a nose with two nostrils. Two kidneys, two lungs, etc. This form hasn't changed because it is efficient, the underlying fractal pattern that governs the growth of our bodies can be compressed efficiently in the instruction manual that is our DNA.
This underlying structure is unlikely to change, hence, it is unlikely that any mammal, reptile, amphibian, or fish, will grow three eyes. It is important to note that the principle differences between, for example, Chimpanzees and Humans, are not actual differences in the content of DNA, but in what sequence and what way the genetic code is activated.
I never miss an opportunity to educate the internets.
