1.8 Million-Year-Old Skull Suggests Three Early Human Species Were One 168
ananyo writes "A 1.8 million-year-old human skull dramatically simplifies the textbook story of human evolution, suggesting what were thought to be three distinct species of early human (Homo habilis, Homo rudolfensis and Homo erectus) was just one. 'Skull 5', along with four other skulls from the same excavation site at Dmanisi, Georgia, also shows that early humans were as physically diverse as we are today (paper abstract)."
Stuff we know and stuff we assume (Score:3, Interesting)
How do scientists know, when it comes to any prehistoric animal or human skeleton, when an individual becomes to a new species, to some sort of missing link or just-split subspecies, and not just a slightly different individual belonging to a known species?
I mean how do they know when a lightly larger bump on a skull is not normal variation and it's for sure a new species where all individuals will have that bump?
What puzzles me is that we find like 0.00000000001 of all living individuals from that time and species and yet we know it's relevant.
Re:Here'e the problem (Score:5, Interesting)
The true definition of species is a group that can and do inter-breed to make offspring. So, the line actually *IS* very clear cut... as soon as a mutation occurs that branches one set so they can no longer reproduce with the other, it is a new species. The problem is, determining that point in history using only archeology is very difficult and full of guesswork. Even if you have the DNA from all 3 sides of the tree, we aren't adept enough yet to be able to look at two pieces of DNA and say "yes these two could reproduce and make viable offspring", vs. "yes these two could reproduce but their offspring would all be sterile". That is when you form a new species.
Re:Here'e the problem (Score:5, Interesting)
A new species is _only_ formed when one line is split into two lines.
Yes, but pinpointing the "split", is quite a problem [wikipedia.org]. You don't need fossils to show this 'problem', it can be seen in what are known as "ring species" that are alive today.
Basically one species spreads both directions along a circular geological boundary. Despite the fact that all individuals along the expanding route can breed with the different races on either side of them, when the two expanding ends of the population meet at the other side of the boundary, they have become distinct species that can no longer interbreed. There is no point along the genetic line where the species forked, yet fork they did since each "end" of the route is a different species.
Another more linear example (like the fossil record) are the changes that occur as a species expands it's range up a tall mountain, there's a continuum of slight genetic variations from the species at the bottom of the mountain to the (different) species at the top. Again, there is no point on the genetic continuum where it can be said the species "split".
Sad comment on the "science" .... (Score:4, Interesting)
5 skulls leading to pronouncements on the species and its evolution?!
5 of several tens or hundreds of thousands is not statistically significant.
This is why creationism can survive, because it at times makes as much sense as the extraordinary extrapolations tossed out by scientists.
Make it right. Demand that the scientists also share possible margins of error (in this case HUGE).