Why aren't our evolutionary ancestors extinct?
- Thread starter EmmZ
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People have been breeding fruit, and selecting fruit, and grafting/cloning/propagating fruit, for thousands of years on at least five continents.john said:
All you have witnessed is artificial extinction. No one has ever seen anything go extinct naturally. So how do you know it ever happens ?john said:
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It depends on the speciation event.
Isolated populations can "drift" into a new species, randomly, with little or no selective pressure. This allopatric speciation can also lead to new species because of selective pressures. For instance, in the isolated Hawaiin island chain, Diptera (flies with two wings, like mosquitos, houseflies, or craneflies) were blown out there tens of millions of years ago. Presumably, there weren't enough predators out there to fill a "predatory bug" niche, so the Diptera ended up filling that niche through positive directional selection. In this case, a new and old species exist.
In alternative scenario, organisms with ancestral traits can survive in remote places where new better adapted plants haven't arrived, like the ancient cycads in Australia, or the ginko tree in Japan (which is believed to have been kept alive by cultivation in temples).
In remote places like Hawaii or Australia, the introduction of animals like the cane toad or rat, dog, pig and cat pose major problems to native flora and fauna, since the introduced organisms can outcompete the local ones. In such cases, we see "more evolved" species driving other ones to extinction.
In places where there aren't entirely new clades of organisms aren't being introduced, the ecosystem has been around since at least the ice age, one presumes that the species present are, for the most part, in equilibrium. The ones that would have gone extinct already have, and we've only been around a thousand years or so to observe and record any changes, most of which were due to us dicking with the environment.
But to more directly answer your question, in most cases, the ancestral species (proper term for your "gateway species") HAS died out, and only its descendants remain. Using phylogenetics, a logical process that looks at organisms that share similar characteristics (typically genetic) and groups them into trees, scientists can infer what the common ancestor looked like. At one point, the entire vertebrate line most likely looked something like this lancelet. But that lancelet itself is descended from an ancestor that we once shared about 500 million years ago- it has undergone extensive evolution since to stay adapted to its environment. Persistence can be a matter of luck or evolving the right things at the right time, or possessing the right suite of pre-adaptations that later allowed for diversification.
Enmos
Valued Senior Member
Fraggle Rocker
Staff member
The most recently evolved large animal species is the polar bear, which arose only 100,000 years ago and its teeth didn't attain their final shape until about 10,000 years ago. The polar bear is the descendant of curious grizzly bears who ventured into the artic region and found an abundant source of food there, but weren't suited for the local environment: an aquatic life during feeding season and temperatures vastly below freezing in the hibernating season. A few grizzlies happened to be bigger, have thicker fur, larger paws, or perhaps just sheer cussedness, and stuck it out. Some survived and some of their descendants had even better adaptation, through selection of genes that were already there or through mutation, and eventually the entire suite of polar bear characteristics was achieved. Meanwhile the grizzlies who remained in the subarctic and temperate zones were doing just fine the way they were and their descendants had no pressure to evolve.
The thing is, there's no "need" for anything.
Nature isn't thinking "well, I want only the best of the best alive, I don't need primitive forms aynomre, so I wipe them out".
Organisms with their particular hereditary traits and modifications just survive at different rates, at different places. Some become extinct, some don't, some are able to enter new territories or ecological "lifestyles".
And the "newer", even if "better" will not always be in an ecological position that would always cause primitive organisms to become extinct.
There will be quite primitive lifeforms that would still be perfectly able to keep living for generations and generations, and nature does not "bother" that they're primitive.
No, I realise my language conveyed emotion but I didn't mean to imply evolution was sentient.
Thanks for the other information, it's quite an intricate and detailed process, one I find immensely fascinating.
'fraid they are babe.
I read something in the New Scientist that claimed Orangutans may be our closest relative.
Care to comment?
http://www.amazon.com/Red-Ape-Orangutans-Origins-Revised/dp/0813340640
Care to comment?
http://www.amazon.com/Red-Ape-Orangutans-Origins-Revised/dp/0813340640
So then we dont know?
Enmos
Valued Senior Member
Enmos
Valued Senior Member
Ha, you said "deal". You're so clever Enmos 
OK, I see the tree chart. Tell me, is it possible for Orangutans to be lesser genetically similar but behaviourally more similar? I don't want to let this one go because I've seen Oragutans get post natal depression, that shows enormous emotional aptitude.
OK, I see the tree chart. Tell me, is it possible for Orangutans to be lesser genetically similar but behaviourally more similar? I don't want to let this one go because I've seen Oragutans get post natal depression, that shows enormous emotional aptitude.