Mickiel, let's say the date was 200,000BC, and let's just assume people were still alive, but in primitive conditions. Ignore whatever the Bible says, this is just a hypothetical situation.
Now, let's say you had three male children: one grew to be tall and muscular, the second grew to be slightly stocky and hairy, and the third was small but agile. Furthermore, it would be fair to say that these children would not be exact replicas of you, right?
This is because of variation within a species. Every life form on the planet is going to have children with slightly different traits to them (but let's not go into why, okay?). Because of this fact, there is variation in a species.
Now let's say it suddenly became cold, and food became scarce. Now let's say, hypothetically, your tall and muscular child was able to survive because his longer limbs enabled him to conserve energy, so he didn't need to eat as much, despite the lack of food. At the same time, your slightly hairy and stocky child was better equipped to stay warm, despite the cold. But. Let's say the small and agile child died in the cold because he didn't have these advantageous traits.
This is called natural selection. The small and agile child did not have the traits required to survive in the environment, so he died, leaving this other two children to survive. This is an example of one of the basic postulates of evolution: that because organisms within a species will have slightly different characteristics, the organism with the best traits suited to help it survive will live on, while the people with the inferior traits will die.
Now let's say that your first son died younger than normal because of heart failure, leaving your second son to live on (the hairy and stocky one). And let's say your hairy and stocky child had children, two who were short, hairy and stocky, and one who was slightly taller. Now let's say that the one who was slightly taller died in the cold environment, and that the remaining two children had kids: one who was the same size as their parents, the second who was even smaller and slightly stockier, and the third who was even stockier than his parents, but about the same height. Let's say only the third child survived. Let's say he had kids. All of whom resembled him to an extent, but each with their own traits.
In comparison, you, the father, look like you do now.
This is how evolution works. It does not say that people "magically transform". It says that because of differences in your offspring, and because some of those differences are beneficial for life, the child with the best genes suited to survive, will survive, and pass on those genes. In all, evolution is the net sum of all inheritable adaptations.
So. In summary:
1. There is variation of traits within a species.
2. This variation of traits are because of differences in genes (DNA).
3. Species will compete for limited resources in a brutal world.
4. The species who is most successfully able to reproduce will do so, and carry on their genes.
5. Natural selection: the organism within a species who has the traits best suited for survival, will carry on their traits, while the organism with inferior traits will die out. As generations progress, only the beneficial traits come to exist, and species gradually change.
6. Proof of this lies in all of the different races of people on Earth. The theory of evolution explains why every race has slightly different traits.