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1.8 Million-Year-Old Skull Suggests Three Early Human Species Were One
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)."
It is not exactly like that. It is rather that any given sample along one line, regardless where it is on the timeline, belongs to only one and the same species, regardless of evolutionary change! A new species is _only_ formed when one line is split into two lines. And even more surprising, to many, then is that neither is the same species as their ancestor, for solely technical reasons.
Man, the real story here is the skull.
It dont really care what it suggests, the mere fact it was talking is creepy...
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.
That's pretty much the problem for the whole field. There are so few complete specimens (we're talking dozens, rather than hundreds) and they're generally so diverse geographically and chronologically that is becomes very difficult to say whether something was "species wide" or just individual variance. So you find a 4 foot tall skeleton on an island and you might be tempted to say "I've found a new miniature-species of human!", conveniently forgetting the fact that you only have one skeleton and dwarfism is a relatively common feature of the only human population we have a good sample of (modern us). That skeleton could have been the only 4 foot tall adult within a 100 mile and 100 year radius, and yet there's no way of telling unless you can find more specimens that agree or disagree. And those specimens may simply not exist to be found.
I've always found fields like archaeology & palaeontology particularly fascinating for this reason. It's one of the few areas of science where there will be some things that simply CANNOT be known, because no evidence has survived of it and we can't ever study the past directly. It is one of the only areas of modern study where there is a real sense of mystery that will never and can never be lifted. Every little discovery we make is like finding a single piece of a 100 million piece jigsaw- you learn something, but the balance of things not known is still colossal.
A new species is _only_ formed when one line is split into two lines.
Yes, but pinpointing the "split", is quite a problem. 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".
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.