Okay, this is going to be a long answer. You might want to read a paragraph at a time, think about it, and think about how *you* would interpret the evidence scientifically. Remember that science can only test things that obey natural laws.
People all over the world have different stories about where we came from. Almost all of these stories contain some supernatural force such as one or more gods or spirits. Science can not be used to test whether any of these stories is right, or even which supernatural story is the best. Any explanation that is scientific has to explain what we see without using any supernatural
explanations. This doesn't mean anyone else's
story is wrong, it just isn't science.
Scientists know we didn't actually
evolve from modern monkeys, but the evidence we
have suggests that we have the same ancestor that they do. There are several lines of evidence that lead scientists to believe that all forms of life evolved from only one or a few forms that first existed about 4 billion years ago. One line of evidence is fossils.
What is a fossil?In the deeper layers of the Earth's crust we find no fossils. Then we find fossils of simple organisms in younger layers. As we go up higher in the rocks, we start finding larger, more complex organisms along with the simple ones. Sometimes we see fossils that look like a step between older fossils and newer ones. As we travel through time (up the layers of rock), we also see some kinds of fossils disappear. These types of plants and animals probably went extinct.
The first primates appeared in the fossil record about 70 million years ago. (What is a primate?) In rocks that are about 3 million years old, the first human-like fossil skeletons were found. They aren't exactly like ours. They are smaller, and their brains would have been rather small compared to ours. They had large canine teeth. In even younger rocks, there are skulls that are larger and had bigger brains. Some of these lines went extinct.
The first skeletons that look like us appear in rocks that are about 200,000 years old.
A second line of evidence comes from looking at the bodies of modern animals. If we look at any
primate, we will find exactly the same bones, even
in primates that spend all of their time in the
trees. We have many other similarities, some you can see on the outside, some are internal, and
some are biochemical. We can use a variety of
tests to see them. For example, if you compare DNA
(what is DNA?), you will find that about 98% of our DNA code is just like that of chimpanzees. The other 2% is what makes us different from them.
Anther kind of evidence is developmental. If we study vertebrates (things with backbones and skulls) as they change before birth (or hatching) we see that at the earliest stage, all look the same. Months before we were born, all of us had gill slits and tails. These things disappeared as we developed inside our mothers. This suggests that our ancestors had a use for these things, even though we don't need them now. Our development is not an exact record of our evolution, but it can give us clues.
Another bit of evidence is found in
"useless" structures on living adult animals. For example, some species of snakes and whales have pelvic and leg bones even though they do not now have legs that are visible. These bones do not 'do' anything, so it seems likely that they're
'leftovers' from ancestors that had legs. Our own small fang-like canines don't have any obvious
use, but could be a leftover from the early
primates. Another such structure is the appendix, which is a "dead end" off your large intestine. In many animals this is a large structure that is used to help digest plants (the cecum). In us it is not only useless, it is dangerous. Many people die from appendicitis.
That is a brief look at the facts that led scientists to come up with an evolutionary explanation for where we came from.
While there are many stories of human origin that include supernatural forces, this is currently the only scientific one.