stevestory
Posts: 13407
Joined: Oct. 2005
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some bits from the salvador link I posted:
| Quote | 18 January 2007
What are the speed limits of naturalistic evolution?
scordova
What are the speed limits of naturalistic evolution? We know from experience it takes time to evolve a species. Would naturalistic evolution be fast enough in geological time to turn a cow into a whale, an ape-like creature into a human? What are the speed limits of evolution?
To give an illustration of just how hard it might be to evolve a population, consider that there are about 6.5 billion people on the planet geographically dispersed. Suppose a single advantageous mutation (say a single point mutation or indel) occurred in a single individual in one of those 6.5 billion people. How long would it take for that mutation to propagate such that every human on the planet had this mutation? It would be a pretty long time. Sufficient numbers of people would have to have their descendants exchange genes for centuries. And this measly change is but one nucleotide in 3,500,000,000 base pairs!
The Darwinists will argue, “but that wasn’t the way it was in the past, it was easier to evolve things millions of years ago.” Perhaps. Evolving a large geographically dispersed population is a colossal problem for Darwinian evolution as you can see. Thus (using DarLogic) since Darwinian evolution is true (cough), we must assume this implies populations in the past were much smaller and “well-stirred” (meaning geographic barriers are dismissed and every individual has the same chance of mating with anyone else in the population). Bear in mind also, the population can’t be too small either, since evolution needs a certain number of individuals to be generating a sufficient number of beneficial mutations.
Haldane
So given optimal conditions, how fast could we evolve a population? Haldane (pictured above), suggested that on average, 1 “trait” per 300 generation could be fixed into a population of mammals. In the modern sense, we can take this “trait” to even be a single nucleotide [in the traditional sense we look for phenotypic traits, but the problem of evolving single nucleotide in the genome still remains, thus for the sake of analysis a single nucleotide can be considered something of a “trait”].
But such change is obviously too slow to account for 180,000,000 differences in base pairs between humans and chimps. [chimps have about 180,000,000 base pairs more DNA than humans, if anyone has better figures, please post]. This poses something of a dilemma for the evolutionary community, and this dilemma has been dubbed, “Haldane’s dilemma”. If Haldane’s dilemma seems overly pessimistic, ponder the example I gave above even for a smaller population (say 20,000 individuals within a 200 mile radius ). In light of this, 1 nucleotide per 300 generations might not seem like a stretch. If anything, Haldane’s dilemma (even by his own admission) seems a bit optimistic!
(snipped stuff)
PS Two books relevant to this discussion by ID proponents are Genetic Entropy by respected Cornell geneticist John Sanford.
Genetic Entropy
and The Biotic Message by Electrical Engineer and pioneer of Discontinuity Systematics, Walter ReMine. |
Once again, we turn to the Index of Creationist Claims:
| Quote |
Claim CB121:
J. B. S. Haldane calculated that new genes become fixed only after 300 generations due to the cost of natural selection (Haldane 1957). Since humans and apes differ in 4.8 × 107 genes, there has not been enough time for difference to accumulate. Only 1,667 nucleotide substitutions in genes could have occurred if their divergence was ten million years ago.
Source:
ReMine, Walter J., 1993. The Biotic Message, St. Paul Science, Inc.
Response:
1. Haldane's "cost of natural selection" stemmed from an invalid simplifying assumption in his calculations. He divided by a fitness constant in a way that invalidated his assumption of constant population size, and his cost of selection is an artifact of the changed population size. He also assumed that two mutations would take twice as long to reach fixation as one, but because of sexual recombination, the two can be selected simultaneously and both reach fixation sooner. With corrected calculations, the cost disappears (Wallace 1991; Williams n.d.).
Haldane's paper was published in 1957, and Haldane himself said, "I am quite aware that my conclusions will probably need drastic revision" (Haldane 1957, 523). It is irresponsible not to consider the revision that has occurred in the forty years since his paper was published.
2. ReMine (1993), who promotes the claim, makes several invalid assumptions. His model is contradicted by the following:
* The vast majority of differences would probably be due to genetic drift, not selection.
* Many genes would have been linked with genes that are selected and thus would have hitchhiked with them to fixation.
* Many mutations, such as those due to unequal crossing over, affect more than one codon.
* Human and ape genes both would be diverging from the common ancestor, doubling the difference.
* ReMine's computer simulation supposedly showing the negative influence of Haldane's dilemma assumed a population size of only six (Musgrave 1999).
Links:
Williams, Robert, n.d. Haldane's dilemma. http://www.gate.net/~rwms/haldane1.html
References:
1. Haldane, J. B. S., 1957. The cost of natural selection. Journal of Genetics 55: 511-524.
2. Musgrave, Ian, 1999. Weasels, ReMine, and Haldane's dilemma. http://www.talkorigins.org/origins/postmonth/sep99.html
3. ReMine, Walter J., 1993. The Biotic Message, St. Paul Science, Inc.
4. Wallace, Bruce, 1991. Fifty Years of Genetic Load - An Odyssey. Cornell University Press. See particularly Chapters 5, 6, 8, and 9.
5. Williams. (See above)
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