Okay, so we've got lots of increases in brain size, and a few decreases. In the cases where we have decreases, we usually have body size decreases as well. More often than not, we have body size decreases which result in a disproportionately large brain size, but occasionally we have a body size increase which results in a disproportionately small brain size. And all of that brings us to the Hobbit.
The authors looked at Homo floresiensis in relation to the Dmanisi hominids, Homo habilis, and a Homo erectus from Ngangdong and found that if we use Dmanisi or habilis as an ancestor, the decrease in brain size and body size isn't exceptionally weird when compared to other primate groups. The mouse lemur decreased in both to a greater degree, for example.
But if you use the Ngangdong erectus as the ancestor, it is a really weird decrease.
So, I guess the question is, is it reasonable to use Dmanisi or Homo habilis as the ancestor and not Homo erectus? And of course, we don't know that yet!
Thanks for the link!
I thought the Dmanisi hominids were H. erectus. Or am I missing something?
It would be less difficult to explain how erectus descendants came to be on Flores than habilis descendants.
The Dmanisi hominids are a little strange. They've got a lot of derived traits that ally them with erectus or ergaster, but the cranial capacity is smaller than other erectines (Dmanisi hominids are around 600 cc, while Homo erectus is about 850-1100).
Plus, they are in Georgia, which is a lot further away from Flores than Ngangdong, which is in Indonesia.