MrDarwin

For part 1, I'm looking for conservative estimates on a couple of numbers that would have to be figured into Haldane's "dilemma":

(1) how long ago did modern humans (i.e., Homo sapiens) appear

(2) how long ago did humans and chimpanzees diverge from their most recent common ancestor?

After somebody provides these numbers, I'll work on part 2.

pangloss

Actually, Haldane did not seem to bother himself with the human-ape question - that is the darling of the creationist crowd.

I don't know who coined the term 'Haldane's dilemma', but it has been used for some time. The 'dilemma' is basically that due to the requirement for one gene to be replaced by a new one during evolution, that is, to go from one or a few in a population to the entire population, a elatively few genes can be replaced in a relatively long time (depending on a number of factors) in species with long generation times and few offspring, such as large mammals. It is observed that there are large differences between related species, and so the 'dilemma'. Haldane used a number of what many consider to be unrealistic assumptions in his formulation (from 1957) - he wrote in his 1957 paper that he believed that his numbers would probably need "drastic revision". For example, Haldane assumed a constant population size. In this sense, I see Haldane's formulations as roughly equivalent to the Hardy-Weinberg equation, sort of a null-hypothesis sort of thing.
Using Haldane's formulation, creationist Walter ReMine 'concluded' that in 10 million years, no more than 1667 beneficial mutations could have become fixed in the lineage leading to humans from an ape-like ancestor. Ignoring for now the fact that the number is off, ReMine 'concluded' - with not a shred of evidence, of course - that this is simply too few changes to account for the differences between humans and 'simians' (which is interesting, because ReMine rants and raves whenever someone compares humans to chimps...). He intimates in his silly book that there needs to be more than 500,000 changes. This is asinine on the face of it, since humans have only some 30-60,000 genes and probably a similar number of non-coding regulatory loci, not to mention the fact that we don't even know exactly what this 'ape-like ancestor' was. In ReMine's wacky world, evolution would HAVE to have altered and replaced the entire genetic complement of the lineage leading to humans more than once.

Shows the pitfalls of pontificating in areas well outside one's sphere of knowledge.

MrDarwin

Although we don't have precise numbers yet, we have estimates of two pieces of information that were not available in Haldane's time: the number of human genes, and the approximate genetic similarity between humans and chimpanzees.

Let's be conservative and take the higher number and say humans have 60,000 genes, and that chimps (as well as the common ancestor of the two species) also have 60,000 genes. This means that, if humans and chimps are 98.5% genetically similar, then as a rough estimate we differ significantly in approximately 900 genes, or each species differs by about 450 genes from our common ancestor.

We also have a better idea about when the common ancestor lived, and how long ago "modern" humans appeared.

Anybody want to do the rest of the math?

(Edited to add that I realize that I'm grossly oversimplifying, but gross oversimplification seems to be what creationists understand best!)

[ March 29, 2002: Message edited by: MrDarwin ]</p>

Automaton

This is indeed far far out of my sphere of knowledge pangloss, but isn't the "cost of selection" only due to the reestablishment of a stable population after a detrimental environmental change causes mass extinction except for those individuals with a certain slightly beneficial allele?

I agree, if all evolution proceeded this way, it would indeed be very very slow. Unfortunately for the creationists, the vast majority of evolution occurs due to survival of the fittest. Thus, I believe, rendering ReMine's "equations" moot.

pangloss

The 'cost' paid is the cost of replacing an allele with another. In order for one allele to replace another in a population, the other allele has to be 'snuffed out'. Those getting snuffed is the cost the population pays. The language is confusing, and the likes of ReMine play it to the hilt. If the new allele is beneficial to the point of, for example, only allowing those possessing to reproduce, then the replacement can be very rapid. It is when one assumes that the population size is constant and the new allel has only a minor selective advantage that the speed goes down.
ReMine is rendered moot by these simple facts:

1. He insists that Haldane's model is 'set in stone', despite the fact that there are many cases in which Haldane's limits are violated. ReMine simply ignores/hand-waves this all away.

2. ReMine does not know what the ape-like ancestor from which humanity evolved was, therefore, he cannot know how many mutations were 'required' to get here form there.

Yet he continues to insist that the number set by Haldane's model produces too few to account for human evolution.

It is his highly biased, egomaniacal (have you ever read this guy? sheesh...) , unsupported dogma-defending spewage and nothing more.

Automaton

Oh, I see. The problem is information on Haldane's dilemma is very, very scarcely available to the general non-scientist population (ie., me). And that which is available is usually some hack creationist's twisted misinformation regurgitated from ReMine or Spetner, which is hardly what one would call reliable. Even my local university library (which is huge) doesn't have many books that specifically deal with evolutionary biology, let alone ones that discuss the dilemma. And don't even get me started on trying to sift through the endless journal archives! I was looking for Haldane's original paper (and some of the later work on the dilemma) for a while, and never found anything of use, just some boring neutralist stuff by Kimura et al. Anyway, speaking of which, you wouldn't have a scanned copy of any relevent articles anywhere would you? It would be greatly appreciated by me and most likely a lot of the other non-scientists here who are interested in this sort of thing.

KC

If you live in the USA, and have access to a fax machine, I can fax you copies of Haldane's original paper and Grant and Flake's nice 1974 review paper of subsequent work regarding the subject.

Cheers,

KC

RufusAtticus

Could you post references for both these papers, so I know where to look?

-RvFvS

KC

Haldane's original paper was:

Haldane, JBS (1957) "The cost of natural selection", Journal of Genetics 55, 511-524

He wrote a subsequent paper on the subject:

Haldane, JBS (1960) "More precise expressions for the cost of natural selection", Journal of Genetics 57, 351-360

Grant and Flake's review paper was:

Grant,V and Flake,RH (1974) "Solutions to the Cost-of-Selection Dilemma", PNAS 71:10 3863-3865

Cheers,

KC

RufusAtticus

Thanks. I didn't want to search all of Haldane's work for the referance.

Maybe I should have just asked ReMine to give me a reference.

-RvFvS