This is a rather complicated question but I will answer for you the best I can. Humans, and all living organisms, evolved from a common ancestor billions of years ago. The very first life form is believed to have emerged about 3.6 billion years ago (1 billion years after the earth was formed) from what is called the “primordial soup”. The first animals didn’t appear on earth until 600 million years ago, and mammals did not exist until 200 million years ago. Our earliest human ancestors came to be about 200,000 years ago (pretty recent compared to the first life form).

For any living organism to remain on earth and survive, it must adapt to the environment that it lives in. There are many ways to adapt and survive on earth which is why there is so much diversity in living things. Animals were able to survive by gaining the ability to move and think, which they used to their advantage to hunt for food and keep away from things that might harm them. That is how our early ancestors came to be millions of years ago. We as humans gained a few special traits that gave us an advantage and allowed us to survive. We have highly evolved brains so that we can reason through problems and “out smart” our predators, and we our bipedal. Bipedalism means we have to ability to walk on two legs. There are many theories as to why humans evolved to walk on two legs. One of them claims that it was to help us move more efficiently when walking across the savannahs of Africa. Another theory claims that it was to help us reach for food in trees and carry it back to our communities to eat. A third model says that bipedalism may have helped with self defense. There are many more theories about how we gained the ability to walk on two legs, but no one knows for sure which is correct. Perhaps many theories are correct, or partly correct, as there were likely many advantages to being able to walk on two legs instead of four.

The reason that we grow and develop is that we (and many other living things) are complicated multicellular organisms. We have brains and hearts and lungs and many other organs that require time to become fully formed and functional. Even plants undergo development from seeds to flowers and trees. Women cannot carry full grown humans in their wombs, therefore we have evolved to develop from a single cell and grow into a small person, which is then born and grows into a full side person outside of its mother’s body. This is all part of adaptation to survival on this planet. Without the ability to adapt and the drive to survive, living organisms would have died out 3.6 billion years ago, right after they started living.

Hope that answered your question! If you have anymore, please ask!