Explaining Darwinism to an Accountant

[The_Barbarian]

Barbarian observes:
Neither of these is strictly true

(attempt to show otherwise)

"At the first step, consisting of all the processes leading to the production of a new zygote (including meiosis, gamete formation, and fertilization), new variation is produced. Chance rules supreme at this step, except that the nature of the changes at a given gene locus is strongly constrained." Ernst Mayr What Evolution Is, p120

It’s more than just that. You see, the likelihood of mutations at different locations is different. So it’s not really random there, either.

DNA loss and evolution of genome size in Drosophila.
by: DA Petrov
Genetica, Vol. 115, No. 1. (May 2002), pp. 81-91.
Mutation is often said to be random. Although it must be true that mutation is ignorant about the adaptive needs of the organism and thus is random relative to them as a rule, mutation is not truly random in other respects. Nucleotide substitutions, deletions, insertions, inversions, duplications and other types of mutation occur at different rates and are effected by different mechanisms. Moreover the rates of different mutations vary from organism to organism.

Barbarian asks:
For the latter, I don’t know of anything random about natural selection. Can you tell us about it?

"This second step is a mixture of chance and determination. Clearly, those individuals with characteristics providing the greatest adaptedness to the current circumstances have the greatest probability of survival. However, there are also many chance elimination factors, so that there is no pure determination even at this step. Everything is somewhat probabilistic." Ibid

Taking Mayr’s statement as evidence that natural selection is random is like saying gravity is random, since rocks fall downhill, but sometimes, through unexpected circumstances, they get moved uphill. Neither gravity nor natural selection are random at all, but intervening effects can alter what they do.

This stuff seems pretty basic; I thought you would have known it … but I get the feeling your objections are more personal than professional.

Take a look. Often, words mean different things in science than they do to the layman. “Random” in mutations, means we can’t predict when one will happen, not that all of them are equally likely, or even that we can’t predict a pattern of mutations. Sometimes, we even know the cause:

Intragenic Variation of Synonymous Substitution Rates Is Caused by Nonrandom Mutations at Methylated CpG
Journal of Molecular Evolution
Kazuhisa Tsunoyama, Matthew I. Bellgard and Takashi Gojobori
Abstract. It has been observed that synonymous substitution rates vary among genes in various organisms, although the cause of the variation is unresolved. At the intragenic level, however, the variation of synonymous substitutions is somewhat controversial. By developing a rigorous statistical test and applying the test to 418 homologous gene pairs between mouse and rat, we found that more than 90% of gene pairs showed a statistical significance in intragenic variation of synonymous substitution rates. Moreover, by examining all conceivable possibilities for the cause of the variation, we successfully found that intragenic variation of synonymous substitutions in mammalian genes is caused mainly by a nonrandom mutation due to the methylation of CpG dinucleotides rather than by functional constraints.

When you make an intelligent objection I’ll be happy to reply but your petulant carping is uninteresting and not worth the time it takes to respond.

If you’ve actually read Mayr’s book, you should have picked up these facts.

To be fit means to possess certain properties that increase the the probability of survival. This interpretation is equally applicable to the “nonrandom survival” definition of natural selection.
Ernst Mayr, What Evolution Is p. 118

Read the whole book. It’s a wonder of clarity, summing up evolutionary theory. But he’s already taught you something, albeit by trial and error.

 

[hecd2]

There are two steps to Darwinian evolution: random mutations which are purely chance

Depends what you mean by pure chance. Biologists say that mutations are random. They do *not *mean, when they say this, that mutations are uncaused, or that they occur with equal probability in all genes, or that all mutations at a given locus are equally probable. What they mean is that mutations are not biased to improve the fitness of the individual.

and natural selection which is a mix of chance and determinism.

Yes, I agree with that.

Will it continue? Well, it is more likely to do so than to recover the huge host of functions that it has lost. Really, for C rudii, there is only one viable trajectory.

This is where it gets more interesting. If there is only one viable trajectory then the outcome is not determined by chance but is predetermined - the game is rigged, the dice are loaded.

But, as I pointed out, evolution is not a process of pure chance and no biologist would claim that it was. The direction of evolution is determined both by the environment and by the history and state of the organism. Tetrapods cannot grow a third pair of limbs, so if they evolve flight, they have to give up the use of their forelimbs to dedicate them to the function of wings. In this case, Carsonella has lost a huge part of its functional genome, hence my prediction.

I don’t believe that deterministic (directed) evolution requires active interference; it can also be brought about by the predetermination of what trajectories are viable. This is what I find significant in your comment predicting how Carsonella will evolve.

Well then, we agree. It is a fallacy promoted by creationists that evolution is purely random and that it can do anything. It is not and it cannot - it is restricted by developmental biology, and by the fitness of organisms in their environment. But note that the trajectories available to Carsonella, in its environment, are immensely more restricted than the trajectories available to free-living organisms. So I cannot predict how, say, Mus musculus will evolve in a million year’s time. Nor would it have been possible to predict, given the starting point of the first placental mammal, that they would evolve into elephants, whales, bats and humans. Nor would we expect to see the same outcome if we could rewind the tape, just as we wouldn’t expect our parents to give birth to us and our siblings, if we could rewind the tape. We should be wary of making predictions about the direction of evolution except in simple cases, such as the one we have been discussing, or cases such as loss of sight in dark cave dwellers.

Alec
evolutionpages.com

 

[Ender]

Biologists say that mutations are random. They do *not *mean, when they say this, that mutations are uncaused, or that they occur with equal probability in all genes, or that all mutations at a given locus are equally probable. What they mean is that mutations are not biased to improve the fitness of the individual.

Agreed. A lot of the argument is over the precise meaning of “random.”

The direction of evolution is determined both by the environment and by the history and state of the organism.

Environment: yes; state: yes; history … I’m not so sure.

But note that the trajectories available to Carsonella, in its environment, are immensely more restricted than the trajectories available to free-living organisms. So I cannot predict how, say, Mus musculus will evolve in a million year’s time.

I accept this. Taking it further, we can look at an organism in a restricted situation (Carsonella) and make a reasonable prediction as to where it will probably evolve where with Mus we cannot make a prediction simply because there are too many options for us to quantify. This, however, may represent only a defect in our knowledge. We assume that Mus can evolve in any number of different ways because we are incapable of distinguishing true paths from imaginary ones; it may actually be that Mus is as restricted in its evolutionary destinations as is Carsonella.

Nor would we expect to see the same outcome if we could rewind the tape, just as we wouldn’t expect our parents to give birth to us and our siblings, if we could rewind the tape.

I don’t think the analogy holds; I’m not convinced that evolutionary history wouldn’t more or less repeat itself. The time periods would surely be different but I’m not sure the organisms would be.

Ender

 

[hecd2]

Agreed. A lot of the argument is over the precise meaning of “random.”

hecd2:

                          The direction of evolution is determined both by the environment and by the history and state of the organism.

Environment: yes; state: yes; history … I’m not so sure.

Perhaps I wasn’t as clear as I could have been. By organism here, I mean population of organisms, and by history I mean evolutionary history. I gave the example earlier of flying tetrapods (ie birds and bats) - because of the evolutionary history of the tetrapod clade, tetrapods are limited to four limbs - if they evolve flight they have to dedicate one pair of limbs to wings. They are developmentally incapable of growing wings and retaining four legs.

I accept this. Taking it further, we can look at an organism in a restricted situation (Carsonella) and make a reasonable prediction as to where it will probably evolve where with Mus we cannot make a prediction simply because there are too many options for us to quantify. This, however, may represent only a defect in our knowledge. We assume that Mus can evolve in any number of different ways because we are incapable of distinguishing true paths from imaginary ones; it may actually be that Mus is as restricted in its evolutionary destinations as is Carsonella.

Well there isn’t one path taken in most cases - evolution shows constant radiation of species from ancestors. I don’t see how we can predict, even in retrospect knowing the evolutionary history, the radiation of the earliest eutherians 125 million years ago into bats, rhinos and whales. And I don’t see how you can say that there were not an almost infinite number of other possible pathways not taken. Sure there are some convergences - sharks, icthyosaurs and dolphins show some similar features - but they are still very different creatures. Organism space is vastly multidimensional and although the paths through it are only a small fraction of the total space available they still represent a practically unlimited variety of creature.

On the other hand, your argument might be that everything is predetermined and that the appearance of randomness is a human illusion resulting from our imperfect knowledge. There are two problems with that: one scientific and one philosophical.

The scientific issue is that quantum uncertainty is truly random - our inability to predict a quantum event remains even if we know everything there is to know about the state of the microsystem. Go here for a discussion of the different meanings of randomness in science that I wrote in response to Cardinal Schoenborn’s attack on science; look in particular at the section titled Dice at the Royal Court:
evolutionpages.com/Schoenborn_critique.htm

The philosophical problem is that strict determinism seems to do away with free will.

Nor would we expect to see the same outcome if we could rewind the tape, just as we wouldn’t expect our parents to give birth to us and our siblings, if we could rewind the tape.

I don’t think the analogy holds; I’m not convinced that evolutionary history wouldn’t more or less repeat itself. The time periods would surely be different but I’m not sure the organisms would be.

See above. I don’t see how we can expect to see the same species evolve unless you accept strict determinism.

Alec
evolutionpages.com