prescriptive grammar - When do we not use definite article, "the"?

I have a question. Could you please explain why “the” is not used in the parts that I have indicated in bold? Why is "the" missing?

Little is known about the lives of early human beings. What we do know has been gathered through the study of ancient caves that scientists called archeologists believe early humans probably lived in.
The evidence suggests that the first human beings lived in caves along the southern coast of Africa. This region provided ample supplies of food as well as a warm climate.

The text above is from https://kidspast.com/world-history/prehistoric-humans/