The Talk.Origins Archive Post of the Month: September 1999

Subject:    ReMine's Dilemma OR size DOES matter
Newsgroups: talk.origins
Date:       September 17, 1999
Message-ID: 37e2b35b.2590293@news.cavva.com.au

(this is my THIRD try at sending this, the rest disappeared into the ether, but might turn up after 3 weeks, as a previous post did)

There has been some discussion on the newsgroups talk.origins and sci.bio.evolution over the last year or so regarding Walter ReMine's claims that a version of Dawkins' "weasel" program, which demonstrates the efficacy of selection, nevertheless demonstrates a serious limitation on the rate of evolution, in agreement with Haldane's Dilemma, a rate so low that Mr. ReMine claims this makes the current accounts of human origins (and other higher vertebrates) implausible
(see http://x38.deja.com/getdoc.xp?AN=294263986 and http://x38.deja.com/getdoc.xp?AN=315954300).

As I have written before, I can't for the life of me see how any Dawkins style "blind watchmaker" program will reproduce Haldane's Dilemma, as Haldane's Dilemma requires multiple genes (typically > 20,000), with a proportion of those genes having multiple alleles (see http://www.gate.net/~rwms/haldane1.html or Natural Selection, George C Williams, 1992, Oxford University Press, chapter 10). How a Dawkins style selection program, with only one "gene" and no population structure, could show Haldane's Dilemma, is not clear. Clearly many other people thought that, including Wesley Elsberry, who produced the Perl program "weasel.pl" (see http://www-personal.monash.edu.au/~ianm/whale.htm) to explicitly explore this claim, and Robert Williams, whose site I referenced above.

One problem is the difficulty in finding details on the program, as when asked on internet fora, Mr. ReMine simply refers questioners to his book, The Biotic Message (http://www1.minn.net/~science), a self-published volume that is relatively hard to come by (for example, see http://x24.deja.com/getdoc.xp?AN=339410120).

Fortunately, Will Pratt of the University of Nevada found a copy, and as a result Robert Williams was able to get a copy of David Wise's program MONKEY (see http://www-personal.monash.edu.au/~ianm/whale.htm), which ReMine used. As I also noted earlier, after running it several times, and looking at the code, I couldn't find any hint of Haldane's Dilemma in the program. What was I missing?

The answer is actually blindingly simple, and is an embarrassment to Mr. ReMine. Here are relevant excerpts from Mr. ReMine's book.

"That method of mutation is not true to nature [used by Dawkins]. In nature nothing counts mutations and assures exactly one in each progeny. A more realistic type of mutation should be used in the simulation so that each letter has a probability of mutation. Suppose we use this correct method of mutation while leaving the "average" rate unchanged (at 1 chance in 28). This subtle correction to the simulation nearly doubles the time needed to evolve the target phrase: to 86 generations."

"Then we reduce the reproduction rate to that of the higher vertebrates, say n=6. In a sexual species this would require the females to produce 12 offspring each. This is overly optimistic for many species. The simulation then goes into error catastrophe and does not reach the target phrase. We can eliminate the error catastrophe by lowering the mutation rate."

"Then by exploration we can find the mutation rate that produces the fastest evolution [footnote: in this case the optimum mutation rate is one in 56]. With this optimal mutation rate, on average, the target phrase is reached in 1663 generations - that is 62 generations per substitution."

"Thus the simulation - with its numerous unrealistic assumptions that favor evolution - is less than five times faster than Haldane's estimate of 300 generations per substitution. Ironically, this suggests that Haldane was too optimistic about the speed of evolution."
<end quotes>

Can you see where ReMine has made his error? I actually wasted a couple of hours comparing the effects of mutation rates on different programs before I realized it, but it should have been blindingly obvious (so I'm stupid, okay, but I was expecting something subtle).

Here's the key line: "Then we reduce the reproduction rate to that of the higher vertebrates, say to n=6."

Well, knock me down with a stick of mortadella and call me Jake. Mr. ReMine doesn't know how these programs work! In the vast majority of weasel simulations, including Wise's, the program takes a string, makes x copies of it with single letter mutations in one or more copies of the string, then chooses the best string and makes x copies of that with mutations, then chooses the best string from those copies, and makes x copies ad infinitum until the target string is reached. In many of these programs, the value x is a user entered variable called "number of offspring" or similar wording.

The important thing to note is that in Wise's program, Dawkins' original, Wesley Elsberry's weasel.pl and my WEASEL4.BAS (see sig) the "reproduction rate", i.e. number of offspring, IS ALSO THE POPULATION SIZE! Of course you will see only slow substitution in any of these programs when you only have 5 offspring, as there is only a TOTAL POPULATION of 5 strings at any one time![1]

Of course, in the real world, most organisms have populations of more than 5 individuals :-). Trying to compare the substitution rate in a population of 5 indviduals with the substitution rate in a population of between 10,000 to 100,000 individuals is a pretty big blunder to make, even allowing for the other problems in trying to compare this program with a real population. The information about "offspring" number isn't hidden, it's clear in the description given by Dawkins and in David Wise's documentation.

ReMine's argument totally collapses, without even having to point out the other, obvious problems.

Cheers! Ian
[1] Think about it, if you did do it the way Mr. ReMine thinks strings are reproduced, then in a few generations an exponentially growing number of strings will exceed the string space of any program.
=========================================================================
(Appendix: Wise's subroutine that generates the "population" from offspring number)

PROCEDURE spawn;

{  SPAWN copies the "parent" string (index 0) into each 
       "offspring" string and then performs the selected "mutation".
NOTE:  in each case, the letter position to be changed is selected at
       random AND the letter to be placed there is also selected at
       random.   }

VAR
  i, j, k :INTEGER;

BEGIN
  FOR i:=1 TO num_copies DO
    BEGIN
    s[i] := s[0];                { Copy the "parent" }
    IF (option <> 3) OR (i > 1)  { Do not change if first child and option }
      THEN                       { is 3(one child remains unchanged) }
        CASE method OF
          1 : s[i,(Random(msg_size)+1)] := letter_pool[Random(pool_size)];
          2 : FOR k:=1 TO num_changes DO
                  s[i,(Random(msg_size)+1)] := letter_pool[Random(pool_size)];
          3 : FOR j:=1 TO msg_size DO
                IF Random < mut_prob
                  THEN
                    s[i,j] := letter_pool[Random(pool_size)];
        END;  {CASE}
    diffs[i] := diff(s[i]);
    END;  {FOR i:=1 TO num_copies DO}
  i := min_diff;                  { find offspring closest to target }
  s[0] := s[i];                   { make the offspring the next parent }
  diffs[0] := diffs[i];           { save its difference for display  }
END;

Weasels, ReMine, and Haldane's Dilemma

Post of the Month: September 1999