Based on depth and distance from the shoreline, how many zones are found in ponds and lakes?

Humans are believed to have evolved in coastal regions in east africa. the region had an abundant supply of fish for early humanoids to eat. when scientists analyze the fads gene they see an interesting pattern. people whose families have lived in this area of east africa for generation show a high level of diversity in alleles for the fads gene. conversely, people whose families had migrated inland a moderate distance from sources of fish showed a much lower diversity for fads gene alleles. additionally, the fads alleles found in people whose family has lived inland for generation are almost all gene alleles which produce fads proteins with a high level of function and activity. how do anthropologists explain this?

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

What organ is the first to receive nutrients that have been absorbed from the digestive tract?