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Author Topic:   Definition of Species
caffeine
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Posts: 1655
From: Prague, Czech Republic
Joined: 10-22-2008
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(1)
Message 102 of 450 (570232)
07-26-2010 11:58 AM
Reply to: Message 92 by Big_Al35
07-26-2010 10:15 AM


Fish
But the ToE states that monkeys didn't evolve from fish...but fish-like creatures.

You do this stuff on purpose don't you?

Ok, fine I should've corrected you on that in your previous post. There, happy now? I didn't correct a mistake you made.

Under what silly definition of fish did monkeys not evolve from them? If we're defining 'fish' as synonomous with 'ray-finned fish' then monkeys didn't evolve from fish, but in this case lungfish aren't fish, sharks aren't fish and all manner of fossil fish groups aren't fish.

Of course monkeys evolved from fish. In a different post you asked what a 'fish-like creature' was. It's a creature like a fish. A fish is a scaly, aquatic vertebrate with fins. Monkeys, along with all other land vertebrates, evolved from scaly aquatic vertebrates with fins.


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caffeine
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Posts: 1655
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 5.7


Message 116 of 450 (570400)
07-27-2010 10:09 AM
Reply to: Message 104 by Big_Al35
07-27-2010 6:45 AM


Re: Complexity of an organism
Things can evolve into simpler forms if this turns out to be better for them. There was a famous experiment conducted with the virus Q-beta, which in the wild normal has a genome length of about 4,500 base pairs, and which creates four different proteins to do its work. Scientists watched it evolve after putting it in environment which already contained the enzyme and the nutrients it needed to replicate itself. Without any necessicity to make any proteins to deal with the challenges it normally faced, the genome eventually reproduced to only a couple of hundred base pairs - not enough to make any proteins and about the minimum necessary to replicate itself. Simplicity was selected for rather than complexity.

The reason people balk at the idea of fish evolving from monkeys isn't because they don't believe animals can get simpler. It's because fish have been around for hundreds of millions of years, while monkeys don't appear in the fossil record until about 35 million years ago. For fish to have evolved from monkeys, there would have to have been monkeys around for about 500 million years without leaving any trace of their existence, monkeys which evolved from ancestors who also left no trace, and who evolved into fish without leaving any trace of animals transitional between fish and monkeys. And then, of course, the rest of the terrestrial verebrates would have somehow had to evolve so as to look exactly as if monkeys were one of them when they finally appear - fitting on neatly to the primate branch of the tree, even at the molecular level.

This is how we know fish never evolved from monkeys.


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caffeine
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Posts: 1655
From: Prague, Czech Republic
Joined: 10-22-2008
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Message 125 of 450 (570662)
07-28-2010 6:51 AM
Reply to: Message 124 by Big_Al35
07-28-2010 6:11 AM


Re: Not even tangential to the original direction.
So if we found the common ancestor we could probably just assume that it was infact only the ancestor for a fish.

Why would you assume this? We know from DNA evidence, and from morphological similarities, that some fish are more closely related to land animals than they are to other fish. So, if we found the common ancestor of all fish, we'd know that it was also the ancestor of land vertrebrates.


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caffeine
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Posts: 1655
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 5.7


(1)
Message 129 of 450 (570687)
07-28-2010 10:07 AM
Reply to: Message 127 by Big_Al35
07-28-2010 9:19 AM


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

We donít have access to the ancestral DNA, no, but we do have access to the DNA of living animals, and this is how the family trees of life are constructed (or, more accurately, how they are refined). Letís say we have three animals Ė A, B and C Ė and we look at their genomes. The genomes of A and B turn out to be much more similar to each other than either is to the genome of C. We assume, then, that A and B share a common ancestor with each other more recently than either does with C. If A and B shared a common ancestor more recently than A and C, then A and B's genome should be more similar, having had less time to diverge from each other. Now imagine that A is a rabbit, B is a lungfish and C is a tuna, and you see why the tree of life is constructed as it is.

It's not just genetic evidence, by the way. Lungfish and coelacanths were grouped with land vertebrates long before there was DNA evidence for it, based on morphological evidence.

quote:
My point is that an ancestral fish was a fish and will have DNA to match this. It will also be more closely related to a modern fish than say a rabbit in terms of its DNA. So it would be safe to assume that an ancient fish was an ancestor of the modern fish.

The ancient fish will probably not have DNA significantly more similar to the modern fish than to rabbits. The DNA of fish has gone through hundreds of millions of years of mutations - just like those of rabbits, and the fish wouldn't be very much alike. The DNA of different fish is very different - a noted above, lungfish are more genetically similar to monkeys than to tuna, while tuna are more genetically similar to elephants than to sharks.

quote:
Now, if you are suggesting that the DNA of some modern fish is more closely related to a rabbits than it is to other fish then dare I say it.....fishy pun.....this would be a red herring. Because these fish are NOT the ancestors of rabbits. They are infact modern fish.

I'm not sure why you think this is relevant. The significant fact about these fish being lumped in with rabbits and monkey's genetically is that their ancestors diverged from those of other fish before they diverged from land vertebrates. This means that the common ancestor of all fish is also an ancestor of land vertebrates. So, even without any fossil evidence, we'd assume that land vertebrates eventually trace their ancestry to fish. This is the simpler explanation, because it just requires a creature that looks like a fish, one of whose descendent lines lost thi distincitve fishiness to become tetrapods. The other possibility, that the common ancestor was not a fish, would require the distinctive features of fishiness to have arisen at least three times independently in different lineages of fish ancestors. Monkeys evolving from fish is the simpler explanation (and, once fossil evidence is taken into account, the only sensible explanation).


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caffeine
Member
Posts: 1655
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 5.7


Message 165 of 450 (572332)
08-05-2010 9:48 AM
Reply to: Message 164 by Big_Al35
08-05-2010 9:43 AM


Re: Species Definition
quote:
We don't even know if TRex was a top predator or just a scavenger.

We can be fairly confident about it. We know that T Rex was not 'just' a scavenger, because fossils of prey animals have been found with wounds inflicted by Tyrannousarus teeth, which have since partially healed, suggesting an unsuccessful hunt.

I read an interesting article about this recently, which I've since lost. Get back to you when I find it.

ABE: Here we go - it was on Dave Hone's blog. Clear evidence has been found of both predation and scavenging in tyrannosaurs.

Edited by caffeine, : No reason given.


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caffeine
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Posts: 1655
From: Prague, Czech Republic
Joined: 10-22-2008
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Message 179 of 450 (572477)
08-06-2010 5:48 AM
Reply to: Message 170 by Big_Al35
08-05-2010 11:05 AM


Re: Species Definition
Yes, that's right...there maybe multiple TRex species. I don't disagree that a lot can still be gleaned from the fossil evidence. However, a lot cannot be gleaned from the fossil evidence. eg we don't know if the TRex was a predator or a scavenger.

As I already pointed out upthread, this isn't true. Evidence of both scavenging and predatory behaviour has been found for tyrannosaurids, which makes sense as most carnivores do both.

But I'm not sure why you think this is significant for species classification. There are all sorts of unanswered questions about the beahviour of living animals. It's a matter of debate whether honey guides lead honey badgers to bee hives - nobody knows for sure. Does this mean we should be dubious about its species classification?


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