Joined: Sep. 2006
|Returning to the genetic markers.|
Imagine a table, and in the middle a perfectly stacked deck of cards ace to kings (call this the common deck). Either side of the table sits ‘Chimp’ and ‘Champ’ both with identical copies of the common deck. Both Chimp and Champ represent lineages to disparate organisms which share genetic markers.
To represent evolution in time both Chimp and Champ are asked to shuffle their cards for a few second - after this they lay their cards down and examine the similarities. It would be expected that both would have small sequences identical to each others and also to the common deck.
This is an interesting thought experiment. But can we determine a nested hierarchy from just two individuals, Chimp and Champ?
Let's assume common descent. If the mutation rate is very high, then genetic evidence (patterns in the deck of playing cards) will be scant or non-existent. This seems to be Acquiesce's point. If the mutation rate is very low, then there will be little evolutionary change.
Of course, it turns out that all organisms on Earth share at least some of their genetic material. Heredity is not random and humans share most of their genes with other apes. We observe the change in genomes and can determine the rate of change is consistent with the change observed over eons of time. So the deck is not "shuffled"; rather small changes accumulate over time.
The pattern of a nested hierarchy is not merely a similarity, but a correlation of various traits. For instance, having mammary glands implies having vertebrae. This can be explained by common descent of mammals from a common vertebrate ancestor. As there are thousands of such correlations, and empirical predictions can be made and verified, this is very strong scientific support for the Theory of Common Descent.
|Quote (Zachriel @ April 09 2007,16:42)|
|Accepting common descent tells nothing about the cause of it.|
Not "nothing" necessarily, but a reasonable distinction. We can accept common descent and reject natural selection as a mechanism.
Nevertheless, Common Descent implies that broad changes have occurred over long periods of time. Acceptance of this basic concept is important before discussing the mechanisms of this change. That's why IDers refuse to commit on something even so obvious. Any child at a natural history museum can see the truth of evolutionary change over time. And detailed scientific investigation only strengthens the case.
So, can we determine a nested hierarchy from just two individuals, Chimp and Champ? No, it takes at least four. And the more the merrier. It turns out that all extant and extinct species fit a single nested hierarchy of descent (with a possible exception at the very root of the tree — at the very limits of observation).
You never step on the same tard twice—for it's not the same tard and you're not the same person.