Explain why cells don't just continue to grow larger as organisms grow larger.

It is a matter of surface area to volume.  The ratio of surface area to volume decreases (as it gets larger, volume increases faster than surface area).  Because of this, cells can only intake so many nutrients and other things they need, meaning growth is limited.  

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.