Member (Idle past 271 days)
Message 23 of 42 (576605)
08-24-2010 6:09 PM
Reply to: Message 1 by sac51495
08-14-2010 2:38 AM
|The topic name - simultaneous evolution - indicates that this is to be a discussion of those characteristics that we see in the world around us which are mutually supportive of one another, and necessary to one another. The question is this: how would these things evolve in the world of an evolutionist?|
|msg 16 Dr A: I recommended that you study examples of "simultaneous evolution" that would show up in the fossil record.|
The specificity of proteins is another example. But note how it is resolved..
What the authors did was mine existing databases of DNA sequence data, pulling out the sequences of the steroid receptors from 29 different vertebrate species.
Then they charted the changes in the DNA sequence in the context of the tree of life as sketched out in the fossil record. The tree they assembled includes all the steroid receptors.
They used this tree to guide ... an analysis of the 3-D structure of the various postulated intermediates in the evolutionary pathway.
The authors accomplished this by making proteins from the "resurrected" genes, then crystallizing them and using X-ray diffraction techniques to determine their precise structures.
Examination of their receptor family tree revealed something interesting. Most vertebrates have highly specific receptors: the corticosteroid receptor isn't strongly stimulated by aldosterone, and vice versa. But some living vertebrates (skates, in particular) show a different pattern: the corticosteroid receptor isn't all that specific for cortisol. Because the ancestral receptor also lacked specificity (as shown in the 2006 paper), the authors concluded that the receptor acquired its discriminating taste at some point between the branching-off of skates (and their kin) and the separation of fish from tetrapods. Their Figure 1 is a little crowded, but it illustrates this nicely:
To follow the evolutionary narrative in this graph, start at the blue circle, which represents the ancestral receptor that was "resurrected" in the 2006 paper and that happily binds to both corticosteroids and aldosterone. (The graphs on the right side of the figure demonstrate the specificity, or lack thereof, of the receptors at different times in history.) There's a branch leading up and to the left, to the various GRs (corticosteroid receptors), and one leading up and to the right, to the MRs (aldosterone receptors). At the green circle, another branching event occurred, 440 million years ago, at which point certain groups of fishes (skates among them) branched off, up and to the right. The receptor at that point is an ancestral corticosteroid receptor, and it still isn't specific for corticosteroids. But the receptor at the yellow circle, in the common ancestor of tetrapods and bony fishes, is specific. The authors conclude that specificity arose between those two points, between 420 and 440 million years ago.
|I don't necessarily plan to get really into this discussion|
of course not.. you might get pinned down..
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