Wednesday, May 15, 2019

Gelernter's Weak Arguments Against Darwinian Evolution in "The Claremont Review of Books"


The spring 2019 issue of The Claremont Review of Books has an essay by David Gelernter entitled “Giving Up Darwin” that summarizes some of the arguments against Darwinian evolution as developed by proponents of “intelligent design” theory at the Discovery Institute.  Gelernter is silent about the many objections to these arguments, and thus he conveys to his readers the impression that these arguments are irrefutable.  Actually, the arguments are so weak as to be easily refuted.

THE ORIGIN OF SPECIES
Gelernter makes four claims.  His first claim is that while Darwinian science rightly explains microevolution (changes within a species), it cannot explain macroevolution (the emergence of new species from ancestral species).  He mentions “changes to fur density or wing style or beak shape” as examples of “the fine-tuning of existing species,” which is microevolution as distinguished from the macroevolutionary origin of species.

He offers no evidence or argumentation to support this first claim.  He simply asserts it as if it were obviously true.  His reference to “beak shape” might be pointing to the famous studies of the finches in the Galapagos Islands by Peter and Rosemary Grant, who have seen changes in beak size and shape on the island of Daphne Major as evolution in action.  Gelernter seems, then, to be suggesting that this shows microevolution (changes within one finch species) but not macroevolution (changes leading to the emergence of a new finch species).

He is silent about the fact that the Grants have observed the evolution of a new species of finch.  In 1981, a large male cactus finch (Geospiza conirostis) mated with a medium ground finch (Geospiza fortis).  They produced offspring who have bred within the hybrid lineage for over 30 years.  Genetic analysis has recently confirmed that this is a distinctive species separate from the other 18 species of finches on the Galapagos Islands. (I have written about this herehere, and here.)

Gelernter is also silent about the fact that some intelligent design proponents (like Michael Behe) and some scientific creationists (like Ken Ham) have admitted that evidence like this proves the Darwinian evolution of new species.  Ham and others have conceded that Darwin proved that species are not fixed, and that new species can evolve, although they argue that since God created separate “kinds” of life in Genesis, this must mean that some taxonomic level of classification (perhaps “families”) must be God’s fixed creation.  Similarly, Behe accepts the Darwinian account of the evolution of species by common descent from ancestral species—including the common descent of chimps and humans.  (I have written about this herehere, and here.)

THE CAMBRIAN EXPLOSION
Gelernter’s second claim is that the “Cambrian explosion”—the seemingly sudden explosion of complex animal forms about 540 million years ago—denies the Darwinian theory of gradual evolution from ancestral forms, because the “predecessors of the Cambrian creatures are missing.”  He is silent about all the fossil evidence for evolutionary predecessors.  There is evidence for multicellular life appearing from about 590 million years ago in China.  Testate amoebae are known from about 750 million years ago.  There are transitional fossils within the Cambrian—such as lobopods (worms with legs), which are intermediate between anthropods and worms.  Most of the animal groups that we are most familiar with—mammals, reptiles, birds, insects, and spiders—appeared after the Cambrian.  Gelernter says nothing about any of this evidence for Darwinian evolution before, during, and after the Cambrian.

THE EVOLUTION OF PROTEIN MOLECULES
His third claim—to which he devotes the most space—is that Darwinian science cannot explain the evolution of protein molecules, because the construction of such complex molecules by random mutation is so incredibly improbable as to be impossible. 

A protein molecule is based on a chain of amino acids with 150 or more elements, with each one chosen from 20 amino acids.  He writes:

So how hard is it to build a useful, well-shaped protein?  Can you throw a bunch of amino acids together and assume that you will get something good?  Or must you choose each element of the chain with painstaking care?  It happens to be very hard to choose the right beads.

                                             .   .   .

What are the chances that a random 150-link sequence will create such a protein [that is functional].  Nonsense sequences are essentially random.  Mutations are random.  Make random changes to a random sequence and you get another random sequence.  So, close your eyes, make 150 random choices from your 20 bead boxes and string up your beads in the order in which you choose them.  What are the odds that you will come up with a useful new protein?

                                          .   .   .

The total count of possible 150-link chains, where each link is chosen separately from 20 amino acids, is 20150 [20 with 150 zeros].  In other words, many, 20150 roughly equals 10195, and there are only 1080 atoms in the universe.

Notice the reasoning here: the fundamental assumption that Darwinian scientists believe that protein molecules arose in evolution by a single all-at-once “at random” trial, and then the assertion that this is probabilistically impossible.  The problem, however, is that this is a “straw man” fallacy, because no Darwinian scientist believes that this is the way evolution works.  On the contrary, scientists believe that biomolecules evolved as the result of a long series of intermediate steps over long periods of time, in which each step was useful in a previous biological context; and this was not purely a “random” process, because while mutations might be random, natural selection is not—natural selection is a directional process that selects variations that are functional for survival and reproduction.  (Notice how, in the second of the three passages quoted above, Gelernter uses the word “random” 6 times in 3 sentences.)
Gelernter treats complex, functional organic structures as vanishingly tiny targets in large search spaces.  He then assumes that evolution must search this space of equiprobable outcomes blindly and randomly to find its target by accident.  This allows him to conclude that the probability of evolution randomly hitting its target in this huge search space is ridiculously improbable.  But this is utterly irrelevant to how evolution by natural selection actually works.
Evolutionary searches take as their starting points already functioning structures.  Evolution never does a global search of all possibilities.  Rather, evolution undertakes a sequence of local searches in the neighborhoods of functional organic structures.
Consider, for example, the human alpha-globin molecule, which is a part of hemoglobin that performs an oxygen transfer function in the blood stream.  This is a protein chain based on a sequence of 141 amino acids.  Choosing from the 20 amino acids common in living systems, the number of potential chains of length 141 is 20141, which is roughly 10183.  And, of course, Gelernter would say that this number is so enormous that the probability of a random search hitting this tiny target—the human alpha-globin molecule—is so low as to be impossible.
But this ignores the fact that a large class of alpha-globin molecules can perform the essential oxygen transfer function, and there is a great variety in alpha-globin molecules across animal species.  This variation shows the record of evolutionary descent.  Humans and chimpanzees have the same arrangement of alpha-globin genes, while other primates show differences from humans and chimps, but similarities to other mammals.
This indicates that the evolution of the human alpha-globin molecule did not search randomly for its target in a huge search space, as Gelernter assumes.  Rather we should say, it started with the alpha-globin molecule of the common ancestors of humans and primates.  The alpha-globin molecules of our primate ancestors functioned well for them.  By starting there, evolution could move step-by-step to select the alpha-globin molecules that would function well for us—to enhance our survival and reproductive fitness.  What matters is not the rarity of functional proteins in the whole conceivable search space of possible amino-acid combinations, but rather isolation within that portion of the space that must be searched (in this case, the variety of functional alpha-globin molecules among primates as the starting point for natural selection in the evolution of the human alpha-globin molecule).
Gelernter asks: “Can you throw a bunch of amino acids together and assume you will get something good?”  Well, no.  But this question is irrelevant to how evolution really works.

THE EVOLUTION OF BODY PLANS
Gelernter’s fourth claim is that Darwinian science cannot explain “the big body-plan changes required by macro-evolution,” because the major mutations required for such big changes in body plans would be fatal.  But in making this claim, he is silent about the emergence over the past 30 years of “evolutionary developmental biology” (Evo-Devo), which resolves this problem.  (Sean Carroll has provided some of the best surveys of this research.) 
The question is how to explain the remarkable diversity of animal life forms, and particularly, how to explain the diversity of animal species from ancestral species. We might assume, as Gelernter does, that the diverse forms of animal bodies must arise from radically different genes. So, for example, we might think that the wing of a fly and the arm of a human being require major genetic mutations. In fact, however, the "tool kit genes" for building animal bodies are remarkably similar across all animals. This became apparent when the human genome project showed that human beings have only about 22,000 genes, which is about the same number as other animals.

The differences between animal species come not from differences in their "tool kit genes" but differences in their "genetic switches," which are devices in DNA that tell tool kit genes when, where, and how to act. The gene controlling the formation of a fly's wing is the same as the gene controlling the formation of a human arm. The difference arises during embryonic development as regulatory genes turn the other genes on and off at different times and places in the body.

The beauty of this explanation is that it allows us to explain the origin of new species. Small changes in the timing and pace of these genetic switches can lead to the evolutionary development of new species. So, for example, a fish with fins can evolve into a fish with primitive legs for crawling onto land, when small changes in the genetic switches move from creating fins to creating legs.

This same evolutionary mechanism can explain what makes us uniquely human, with our human capacities for thinking, feeling, and acting. Our human uniqueness depends on the uniqueness of our brains in their size and complexity. The evolution of those brains from smaller and simpler primate brains could arise from evolutionary changes in the genetic regulation of the development of primate brains and nervous systems.

As a consequence of that evolution of the brain, we human beings can debate the truth of Darwinian science and of alternatives like intelligent design theory and scientific creationism.  If we use our brains properly, we can see through the specious arguments against Darwinian evolution, like those offered by Gelernter.
I have written a series of posts on the evidence for evolution (herehere, and here.)

3 comments:

Roger Sweeny said...

I fear your number three would not convince Gelertner. He would simply say, "I don't doubt that it is a small step from primate alpha-globin to human alpha-globin. I think micro-evolution is possible. It's the getting from nothing to primate alpha-globin that seems impossible. From nothing to ten to the 183rd power is a search through an almost infinite space. Effectively impossible; we both agree on that. Now, if you can give me a reason to believe it is possible to go from nothing to one amino acid and then to two and eventually to twenty with a complicated folding mechanism thrown in, well maybe ..."

Larry Arnhart said...

If "getting from nothing" means explaining the origin of life, then, yes, that remains a mystery.

But if one can explain the evolution of human alpha-globin from primate alpha-globin, that would seem to be what Gelernter identifies as "macro-evolution--the emergence of new forms of organism, versus mere variation on existing forms."

Or are you suggesting that he could say that the entire evolutionary history of life from the first form of life to humans is "mere variation on existing forms"? If so, then he would be conceding that Darwinian evolution can explain the whole history of life, but not the origin of life.

Roger Sweeny said...

I'm suggesting that he would say going from one 141 amino acid protein to a slightly different 141 amino acid protein is "microevolution" and not a big deal. That it is not a reason to believe in "macroevolution".

That in order to convince him, you would have to show smaller, less complex proteins evolving into larger, more complex proteins. Maybe not necessarily all the way back to the first one--as you say, "the origin of life ... remains a mystery"--but definitely not beginning with 141 amino acids either.