Life evolves because of mutations, genetic drift and natural selection. All individuals have hereditary material in the form of genes that are received from their parents, then passed on to their offspring. The offspring differs from the parent in minor random ways. If those differences are helpful, the offspring is more likely to survive and reproduce. This means that more offspring in the next generation will have that helpful difference. In this way, traits that result in organisms being better adapted to their living conditions become more common in descendant populations. These differences accumulate resulting in changes within the population. This process is responsible for the many diverse life forms in the world.
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Evolution doesn't have a specific path. As Charles Darwin said, it's not the strongest or the most intelligent of the species that survives, but the one that is the most adaptable to change. Natural selection and the random mutations can change the global biological map a lot. For example, the dolphins are actually descendants of terrestrial mouse-like mammals, who entered the water roughly 50,000,000 years ago. So... yeah... a mouse could evolve into a person... almost...
I think it's a good idea to begin this topic with a few older predictions about the future man.
If you think you know everything about Superman, think again. When Joe Schuster and Jerry Siegel created Superman back in the 1930s, they conceived him as a literally superhuman creature, and probably as neat an encapsulation of the popular idea of the future of man as there could be. In the original version of the story, Superman's Krypton was a world where evolution was millions of years more advanced than on Earth and whose inhabitants were possessed of superhuman abilities as a matter of course. The early Superman's powers didn't include anything magical such as flying or heat vision, but he was an idealised and exaggerated version of desirable human abilities. He was incredibly strong, fast, impervious to anything short of a direct hit from a tank round, incredibly intelligent and could see through solid objects, because his senses were more developed than those of ordinary mortals.
In 1933, anthropologist H. L. Shapiro wrote the article "Man—500,000 Years From Now
". in his article, Shapiro said that the man of tomorrow would have a larger brain, rounder and smoother features, a simpler digestive tract (if eating hadn't been made totally obsolete), fewer and smaller teeth, greater height, and only eight toes.
In 1893, H. G. Wells wrote a small article called "The Man of the Year Million", in which he speculated about what the human race of the year 1,000,000 AD would look like. The development of man's technology in the distant future has meant that he relies less and less on his body and more and more on his brain. The technology of the future will produce machines that will take care of all of the chewing and digesting of food, so that the human digestive system will be literally as simple as that of an intestinal parasite that soaks up its food by just sitting in a bath of nutrients. With the transportation systems of the future, legs, torsos, and practically all muscles will become useless and will wither away, until our descendents become huge brains that walk about on their hands.
But why wait so long? Why we can't just help ourselves to evolve from Homo Sapiens to Homo Superior? Are we supposed to wait around until evolution makes all the job for us? Not necessarily. In the '30s and '40s, Doc Savage was also one of the main inspirations for Superman, though Doc Savage was a fantasy hero with at least a nodding acquaintance with reality. Where Superman started out as a super-evolved being, Doc Savage was a pulp fiction ideal of what man could become through hard work, scientific training, and owning a secret gold mine in Central America. Able to outdo anyone anywhere at anything, he was the epitome of the idea that the way to become the man of the future was by willpower and exercise. From that point of view, everybody can evolve into Homo Superior!
But why evolve into a Homo Superior, when you can build one? If you are familiar with science fiction, you'll have loads of options. You can try vivisection like Dr. Moreau, cosmic rays, radium treatments, gland transplants, serums, hormones, electric charges, drugs and even cybernetic implants. Those implants may add "paranormal" abilities in the people of tomorrow, like telepathy and telekinesis.
Last but not least...
Remember that the future could be more surrealistic than we thought. According to some futurists, humans will achieve digital immortality by uploading their minds to computers by 2045. Is it possible the humans of the future dehumanized after all?