Thursday, February 7, 2013

H Allen Orr on Mind and Cosmos by Thomas Nagel; New York Review of Books.

Orr has written a thoughtful and calm critique of Nagel's new book. Nevertheless, along with the hysterical critics, he fails to engage nagel's oint - even those he quotes at length. Below is a critical example. I hope to add more.


Nagel believes that materialism confronts two classes of problems. One, which is new to Nagel’s thought, concerns purported empirical problems with neo-Darwinism. The other, which is more familiar to philosophers, is the alleged failure of materialism to explain consciousness and allied mental phenomena.

Nagel argues that there are purely “empirical reasons” to be skeptical about reductionism in biology and, in particular, about the plausibility of neo-Darwinism. Nagel’s claims here are so surprising that it’s best to quote them at length:

[I am adding the numerals – D.G.]

I would like to defend the untutored reaction of incredulity to the reductionist neo-Darwinian account of the origin and evolution of life. (1) It is prima facie highly implausible that life as we know it is the result of a sequence of physical accidents together with the mechanism of natural selection. (2) We are expected to abandon this naïve response, not in favor of a fully worked out physical/chemical explanation but (3) in favor of an alternative that is really a schema for explanation, supported by some examples. (4) What is lacking, to my knowledge, is a credible argument that the story has a nonnegligible probability of being true. There are two questions. (4a) First, given what is known about the chemical basis of biology and genetics, what is the likelihood that self-reproducing life forms should have come into existence spontaneously on the early earth, solely through the operation of the laws of physics and chemistry? (4b) The second question is about the sources of variation in the evolutionary process that was set in motion once life began: In the available geological time since the first life forms appeared on earth, what is the likelihood that, as a result of physical accident, a sequence of viable genetic mutations should have occurred that was sufficient to permit natural selection to produce the organisms that actually exist?

[[Let’s take stock. Nagel is making five points. (1) Our intuition rebels at the thought that life is the result of an unguided process. (2) We are supposed to abandon that intuition (3) in favour of an idea which at present is only a schema, not an articulated theory. (4) The chief schematic element is the lack of any reason to believe that the probability of truth of the idea is non-negligible. This lack of reason applies to specific areas: (4a) the origin of life [self-replicators], and (4b) adequate sources of variation based solely on accidental changes to genetic material. Note that (4), (4a) and (4b) point out lack of reason to believe in non-negligible probability.

Now let’s look at Orr’s discussion below and see if we can find answers to these five points.]]

Nagel claims that both questions concern “highly specific events over a long historical period in the distant past, the available evidence is very indirect, and general assumptions have to play an important part.” He therefore concludes that “the available scientific evidence, in spite of the consensus of scientific opinion, does not in this matter rationally require us to subordinate the incredulity of common sense.”

[[Right, since very indirect evidence for highly specific events in the distant past does not give adequate reason to believe in non-negligible probability of truth.]]

This conclusion is remarkable in a couple ways. For one thing, there’s not much of an argument here. Instead Nagel’s conclusion rests largely on the strength of his intuition. His intuition recoils from the claimed plausibility of neo-Darwinism and that, it seems, is that.

[[Look at that sentence again. What happened to points (2)-(4b)!?!]]

(Richard Dawkins has called this sort of move the argument from personal incredulity.) But plenty of scientific truths are counterintuitive (does anyone find it intuitive that we’re hurtling around the sun at 67,000 miles per hour?) and a scientific education is, to a considerable extent, an exercise in taming the authority of one’s intuition. Nagel never explains why his intuition should count for so much here.

[[Again, look at (2)-(4b). Is there any comparison to the motion of the earth here? Is the motion of the earth a highly specific fact in the distant past for which we have only very indirect evidence?]]

As for his claim that evolutionary theory is somewhat schematic and that it concerns events that happened long ago, leaving indirect evidence, this is partly true of any historical science, including any alternative to neo-Darwinism, e.g., the one that Nagel himself suggests.

[[So what? We are discussing a reason to abandon a strong intuition. Maybe other historical sciences do not challenge such intuitions. Or maybe they too should be rejected!]]

In any case, a good part of the evidence for neo-Darwinism is not indirect but involves experiments in which evolutionary change is monitored in real time.2

[[Don't worry about the footnote. It refers to evolutionary change in bacteria only, and that has been roundly criticised here: [download the pdf and look for bacterial speciation].]]

More important, Nagel’s conclusions about evolution are almost certainly wrong. The origin of life is admittedly a hard problem and we don’t know exactly how the first self-replicating system arose. But big progress has been made. The discovery of so-called ribozymes in the 1980s plausibly cracked the main principled problem at the heart of the origin of life.

[[Read that sentence again. “Plausibly cracked the main problem.” That means we do not know for sure the main problem has been cracked. And even if it has – the main problem indicated that the natural origin of DNA-proteins is impossible. Plausibly cracking that problem only shows that it is possible. But Nagel’s claim is that we have no reason to think it is probable. Noting Orr says here relates to Nagel’s point. ]]

Research on life’s origin had always faced a chicken and egg dilemma: DNA, our hereditary material, can’t replicate without the assistance of proteins, but one can’t get the required proteins unless they’re encoded by DNA. So how could the whole system get off the ground?

Answer: the first genetic material was probably RNA, not DNA. This might sound like a distinction without a difference but it isn’t. The point is that RNA molecules can both act as a hereditary material (as DNA does) and catalyze certain chemical reactions (as some proteins do), possibly including their own replication. (An RNA molecule that can catalyze a reaction is called a ribozyme.) Consequently, many researchers into the origins of life now believe in an “RNA world,” in which early life on earth was RNA-based. “Physical accidents” were likely still required to produce the first RNA molecules, but we can now begin to see how these molecules might then self-replicate.

Nagel’s astonishment that a “sequence of viable genetic mutations” has been available to evolution over billions of years is also unfounded.3 His concern appears to be that evolution requires an unbroken chain of viable genetic variants that connect the first living creature to, say, human beings. How could nature ensure that a viable mutation was always available to evolution?

[[Hmmm – “his concern seems to be….” – does that not sound like an invitation to a straw man? “I guess this is bothering Nagel, so here is the answer….” But nothing in Nagel’s words suggest so naïve an idea. Even taking all the extinctions into account, and without species chauvinism [or order, or class chauvinism], Nagel says that the evidence for availability of mutations does not make the story probable. Nothing Orr says casts doubt on Nagel’s statement.]]

The answer is that it didn’t. That’s why species go extinct. Indeed that’s what extinction is. The world changes and a species can’t find a mutation fast enough to let it live. Extinction is the norm in evolution: the vast majority of all species have gone extinct. Nagel has, I think, been led astray by a big survivorship bias: the evolutionary lineage that led to us always found a viable mutation, ergo one must, it seems, always be available. Tyrannosaurus rex would presumably be less impressed by nature’s munificence.4