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Author Topic:   Definition of Species
crashfrog
Inactive Member


Message 85 of 450 (569740)
07-23-2010 3:41 PM
Reply to: Message 83 by barbara
07-23-2010 1:11 PM


Re: Speciation discussion, expectations and reality
I don't know how science can build their models of speciation since humans have directly or indirectly affected the course of natural evolution.

But, of course this was the great insight of Darwin - it doesn't matter. Darwin was observing a breeder of pigeons - watching the breeder select the best-suited individuals from his flock to be mated with each other, and the worst-suited individuals become the sunday roast - when he realized it works the same way in the natural world.

In the natural world, those that are possessed of the adaptations crucial for survival in their environment survive and prosper, and most importantly <I>mate</I>, and those that do not quickly become someone's lunch. It's no different than the selection by the pigeon breeder, except that it's the natural world doing it all on its own, so he called it "natural selection."

Humans do have an effect on the species around us. Frequently a detrimental one. But to the species themselves, it doesn't matter. They don't and can't distinguish between a "natural" change in their environment and a human one.

DNA that is currently the model we are using to trace today's living organisms back to their ancestors is going to be difficult and very confusing and it is not going to make sense since human influence has changed the normal flow of gene mutation and natural selection is now not natural in many species that we share this planet of today.

We haven't. And even if we have it doesn't matter. To DNA there's no difference at all between a change in the environment due to natural causes (say, a forest fire) and a change in the environment due to human causes (say, logging.)

To DNA there is only random mutation and natural selection. The same phenomenon used by the pigeon breeder to alter pigeon populations is at work in nature, altering species by natural, unguided means.

Just this fact alone, we have to consider if humans have the ability to affect and alter nature, then some other mechanism also had the ability to alter global landscaping and all of the organisms that supported it in the past.

That mechanism is natural selection and random mutation.


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 Message 83 by barbara, posted 07-23-2010 1:11 PM barbara has not yet responded

  
crashfrog
Inactive Member


Message 130 of 450 (570736)
07-28-2010 2:11 PM
Reply to: Message 127 by Big_Al35
07-28-2010 9:19 AM


Re: Not even tangential to the original direction.
We DON'T have access to ancestral DNA so we can't deduce what you have deduced above.

We have access to it because they passed it along to their descendants when they reproduced.

So it would be safe to assume that an ancient fish was an ancestor of the modern fish.

And then the ancestor of that ancient fish would be something that was not a fish, some finless marine chordate perhaps.


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 Message 127 by Big_Al35, posted 07-28-2010 9:19 AM Big_Al35 has not yet responded

  
crashfrog
Inactive Member


Message 206 of 450 (573262)
08-10-2010 3:49 PM
Reply to: Message 204 by Big_Al35
08-10-2010 8:18 AM


Re: Species Definition vs what matters (and why)
If you think DNA can determine parenthood and lineage, why don't you think it can determine when species are related?

Since those are the same thing, how could DNA be used to do one and not the other?


This message is a reply to:
 Message 204 by Big_Al35, posted 08-10-2010 8:18 AM Big_Al35 has not yet responded

  
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