We as humans have been around for a while. Why are we not "mutated" to our environment.
Our species first appeared less than 200,000 years ago. That's not a very long time. We mutated from an earlier species,
Homo erectus, in about half a million years. That's a pretty reasonable speed.
A few species have developed more quickly, but many have also done it more slowly. The polar bear evolved from the black bear in just about 100,000 years, which was very fast. But there was tremendous environmental pressure favoring that evolution. An ice age presented an entire new habitat and food supply: colder weather requiring a thick layer of fat, a snow pack requiring white fur for camouflage, and an aquatic environment requiring adaptation to a marine life.
And while modern humans,
Homo sapiens, have existed in our current form for a long time, polar bears have been adapting almost right up to this moment. Their current dentition only stabilized about 10,000 years ago. And the polar bear can still mate and hybridize with the black bear--their ranges don't overlap so it seldom happens, but the DNA is compatible. Modern humans were also able to hybridize with
Homo neanderthalensis. As Arauca pointed out, Europeans have a noticeable mixture of Neanderthal DNA, because their ranges overlapped for about 20,000 years in Europe.
The bald eagle speciated from the sea eagle about ten thousand years ago. But those two birds are much more similar than brown bears and polar bears, or modern humans and Neanderthals.
I don't understand why humans are not "changing." We should have had changes like Darwin suggested right?
We are. Don't be so impatient. This process is much slower than you seem to believe. Your biology teachers didn't do a very good job.
Neanderthal's I think are a different class of human species, they don't count.
Yes.
Homo neanderthalensis and
H. sapiens are two distinct species. This was not known for sure until DNA analysis was possible, so older textbooks often count Neanderthals and us as two subspecies of a single species. But that's wrong.
Eskimos are adapted for the cold, Africans are adapted to tropical conditions, a large number of people have mutated so they can now digest milk into adulthood, Europeans have adapted to the plague... how many more examples do you need?
Those aren't necessarily mutations, just selective breeding. Those genes exist, but certain environments select for them.
For example, whenever a human population migrates south, the individuals with more melanin in their skin have a survival advantage because melanin blocks sunlight and prevents them from getting skin cancer. But when a population migrates north, the individuals with more melanin are at a disadvantage, because by blocking out sunlight it causes a vitamin D deficiency in latitudes where the sun is not directly overhead. This is why the Lithuanians have very light skin and the Bengalis have very dark skin, even though their ancestors, the Eastern Indo-Europeans, were a single tribe only 3,500 years ago.
There is no environmental pressure to grow fur - we wear coats.
The key mutation in humans was the expansion of the forebrain. In proportion to body size, it's about four times larger than any other primate. We have a singular ability to override instinctive behavior with reasoned and learned behavior. This allows us to overcome nature. Instead of having to mutate larger bodies, a higher fat content, shorter appendages and thicker hair to conserve body heat, we just kill other animals with our clever flint blades, eat their fat and wear their fur coats.
We don't even change skin tone as we migrate any more. People of African ancestry who live in Norway will always have dark skin because they take vitamin D supplements, and people of European ancestry who live in Somalia will always have light skin because they use sunblock. We have eliminated the need to evolve.
We don't even let ourselves evolve for health reasons. Anybody want to bet that Stephen Hawking has been cajoled into donating to a sperm bank, and it's being auctioned for big bucks to women who want it? Don't expect to find that in Wikipedia.
