According to the concept of survival of the fittest if a population of birds eat worms

The fittest worms will survive the attack and the weaker worms will be eaten

Droughts cause very arid places such as a desert

Many archeologists and anthropologists disagree with dr. thorne's view.  thorne strongly believes that what many calls "homo erectus"  was in fact  homo sapiens,  and that they migrated out of africa almost 2 million years ago and dispersed throughout europe and asia. that's way different  from what scientists have always believed about the evolution of the species.