Friday, December 02, 2005


The following passage is a complete section from Richard Dawkin's book, THE ANCESTOR'S TALE. So clear, so beautiful and, I believe, if read with care, a description of just how inhibited all animal freedoms are, specially the paragraph which relates the situation of beavers raised in a cage.

You know, I like to imagine I'm free, and I say that I started to get interested in all these matters when I picked up the book, CONSCIOUSNESS EXPLAINED by Daniel Dennett, as if I made a choice to pick that book up. Yet, what led me to that book. An accident? Or something else that had flown into my consciousness. Was it the book that I picked up in my 20s, called, THE ORIGINS OF CONSCIOUSNESS IN THE BREAKDOWN OF THE BICAMERAL MIND? Why did I pick that book up? What was in my head when I picked it up, what trigger? How had the synaptical pattern which caused me to pick up the book arrived in my head? Back, back, back the search goes to find the original synapse, or the formation of that connection, which led me to pick up the book. If nothing else, all the synaptical connections in my brain commence in pre-conscious experiences even as far back as to my experiences in my mother's womb.

This is a long one, more than 2,000 words, but fascinating unless you're a fundamentalist Christian and have all the answers anyway.

[Open quote.] THE BEAVER'S TALE

A 'PHENOTYPE' is that which is influenced by genes. That pretty much means everything about a body. But there is a subtlety of emphasis which flows from the word's etymology. "Phaino" is Greek for 'show', 'bring to light, 'make appear', 'exhibit', 'uncover', 'disclose', 'manifest' The phenotype is the external and visible manifestation of the hidden genotype. The Oxford English Dictionary defines it as 'the sum total of the observable features of an individual, regarded as the consequence of the interaction of its genotype with its environment' but it precedes this definition by a subtler one: 'A type of organism distinguishable from others by observable features.'

Darwin saw natural selection as the survival and reproduction of certain types of organism at the expense of rival types of organism. 'Types' here doesn't mean groups or races or species. In the subtitle of The Origin of Species, the much misunderstood phrase 'preservation of favoured races' most emphatically does not mean races in the normal sense. Darwin was writing before genes were named or properly understood, but in modern terms what he meant by 'favoured races' was 'possessors of favoured genes'.

Selection drives evolution only to the extent that the alternative types owe their differences to genes: if the differences are not inherited, differential survival has no impact on future generations. For a Darwinian, phenotypes are the manifestations by which genes are judged by selection. When we say that a beaver's tail is flattened to serve as a paddle, we mean that genes whose phenotypic expression included a flattening of the tail survived by virtue of that phenotype. Individual beavers with the flat-tailed phenotype survived as a consequence of being better swimmers; the responsible genes survived inside them, and were passed on to new generations of flat-tailed beavers.

At the same time, genes that expressed themselves in huge, sharp incisor teeth capable of gnawing through wood also survived. Individual beavers are built by permutations of genes in the beaver gene pool. Genes have survived through generations of ancestral beavers because they have proved good at collaborating with other genes in the beaver gene pool, to produce phenotypes that flourish in the beaver way of life.

At the same time again, alternative cooperatives of genes are surviving in other gene pools, making bodies that survive by prosecuting other life trades: the tiger cooperative, the camel cooperative, the cockroach co-operative, the carrot cooperative. My first book, The Selfish Gene, Could equally have been called The Cooperative Gene without a word of the book itself needing to be changed. Indeed, this might have saved some misunderstanding (some of a book's most vocal critics are content to read the book by title only). Selfishness and cooperation are two sides of a Darwinian coin. Each gene promotes its own selfish welfare, by cooperating with the other genes in the sexually stirred gene pool which is that gene s environment, to build shared bodies.

But beaver genes have special phenotypes quite unlike those of tigers, camels or carrots. Beavers have lake phenotypes, caused by dam phenotypes. A lake is an extended phenotype. The extended phenotype is a special kind of phenotype, and it is the subject of the rest of this tale, which is a brief summary of my book of that title. It is interesting not only in its own right but because it helps us to understand how conventional phenotypes develop. It will turn out that there is no great difference of principle between an extended phenotype like a beaver lake, and a conventional phenotype like a flattened beaver tail.

How can it possibly be right to use the same word, phenotype, on the one hand for a tail of flesh, bone and blood, and on the other hand for a body of still water, stemmed in a valley by a dam? The answer is that both are manifestations of beaver genes; both have evolved to become better and better at preserving those genes; both are linked to the genes they express by a similar chain of embryological causal links. Let me explain.

The embryological processes by which beaver genes shape beaver tails are not known in detail, but we know the kind of thing that goes on. Genes in every cell of a beaver behave as if they 'know' what kind of cell they are in. Skin cells have the same genes as bone cells, but different genes are switched on in the two tissues. We saw this in the Mouse's Tale. Genes, in each of the different kinds of cells in a beaver's tail, behave as if they 'know' where they are. They cause their respective cells to interact with each other in such a way that the whole tail assumes its characteristically hairless flattened form. There are formidable difficulties in working out how they 'know' which part of the tail they are in, but we understand in principle how these difficulties are overcome; and the solutions, like the difficulties themselves, will be of the same general kind when we turn to the development of tiger feet, camel humps and carrot leaves.

They are also of the same general kind in the development of the neuronal and neurochemical mechanisms that drive behavior. Copulatory behavior in beavers is instinctive. A male beaver's brain orchestrates, via hormonal secretions into the blood, and via nerves controlling muscles tugging on artfully hinged bones, a symphony of movements. The result is precise coordination with a female, who herself is moving harmoniously in her own symphony of movements, equally carefully orchestrated to facilitate the union. You may be sure that such exquisite neuromuscular music has been honed and perfected by generations of natural selection. And that means selection of genes. In beaver gene pools, genes survived whose phenotypic effects on the brains, the nerves, the muscles, the glands, the bones, and the sense organs of generations of ancestral beavers improved the chances of those very genes passing through those very generations to arrive in the present.

Genes 'for' behaviour survive in the same kind of way as genes 'for' bones, and skin. Do you protest that there aren't 'really' any genes for behavior; only genes for the nerves and muscles that make the behavior? You are still wrecked among heathen dreams. Anatomical structures have no special status over behavioural ones, where 'direct' effects of genes are concerned. Genes are 'really' or 'directly' responsible only for proteins or other immediate biochemical effects. All other effects, whether on anatomical or behavioural phenotypes, are indirect. But the distinction between direct and indirect is vacuous. What matters in the Darwinian sense is that differences between genes are rendered as differences in phenotypes. It is only differences that natural selection cares about. And, in very much the same way, it is differences that geneticists care about.

Remember the 'subtler' definition of phenotype in the Oxford English Dictionary: 'A type of organism distinguishable from others by observable features'. The key word is distinguishable. A gene 'for' brown eyes is not a gene that directly codes the synthesis of a brown pigment. Well, it might happen to be, but that is not the point. The point about a gene 'for' brown eyes is that its possession makes a difference to eye colour when compared with some alternative version of the gene—an 'allele' The chains of causation that culminate in the difference between one phenotype and another, say between brown and blue eyes, are usually long and tortuous. The gene makes a protein which is different from the protein made by the alternative gene. The protein has an enzymatic effect on cellular chemistry, which affects X which affects Y which affects Z which affects . . . a long chain of intermediate causes which affects . . . the phenotype of interest. The allele makes the difference when its phenotype is compared with the corresponding phenotype, at the end of the correspondingly long chain of causation that proceeds from the alternative allele. Gene differences cause phenotypic differences. Gene changes cause phenotypic changes. In Darwinian evolution alleles are selected, vis a vis alternative alleles, by virtue of the differences in their effects on phenotypes.

The beaver's point is that this comparison between phenotypes can happen anywhere along the chain of causation. All intermediate links along the chain are true phenotypes, and any one of them could constitute the phenotypic effect by which a gene is selected: it only has to be 'visible' to natural selection, nobody cares whether it is visible to us. There is no such thing as the 'ultimate' link in the chain: no final definitive phenotype. Any consequence of a change in alleles, anywhere in the world, however indirect and however long the chain of causation, is fair game for natural selection, so long as it impinges on the survival of the responsible allele, relative to its rivals.

Now, let's look at the embryological chain of causation leading to dam-building in beavers. Dam building behaviour is a complicated stereotypy, built into the brain like a fine-tuned clockwork mechanism. Or, as if to follow the history of clocks into the electronic age, dam building is hard wired in the brain. I have seen a remarkable film of captive beavers imprisoned in a bare, unfurnished cage, with no water and no wood. The beavers enacted, 'in a vacuum' all the stereotyped movements normally seen in natural building behaviour when there is real wood and real water. They seem to be placing virtual wood into a virtual dam wall, pathetically trying to build a ghost wall with ghost sticks, all on the hard, dry, flat floor of their prison. One feels sorry for them: it is as if they are desperate to exercise their frustrated dam-building clockwork.

Only beavers have this kind of brain clockwork. Other species have clockwork for copulation, scratching and fighting, and so do beavers. But only beavers have brain clockwork for dam-building, and it must have evolved by slow degrees in ancestral beavers. It evolved because the lakes produced by dams are useful. It is not totally clear what they are useful for, but they must have been useful for the beavers who built them, not just any old beavers. The best guess seems to be that a lake provides a beaver with a safe place to build its lodge, out of reach for most predators, and a safe conduit for transporting food. Whatever the advantage it must be a substantial one, or beavers would not devote so much time and effort to building dams. Once again, note that natural selection is a predictive theory. The Darwinian can make the confident prediction that, if dams were a useless waste of time, rival beavers who refrained from building them would survive better and pass on genetic tendencies not to build. The fact that beavers are so anxious to build dams is very strong evidence that it benefited their ancestors to do so.

Like any other useful adaptation, the dam-building clockwork in the brain must have evolved by Darwinian selection of genes. There must have been genetic variations in the wiring of the brain which affected; dam-building. Those genetic variants that resulted in improved dams were more likely to survive in beaver gene pools. It is the same story as for all Darwinian adaptations. But which is the phenotype? At which link in the chain of causal links shall we say the genetic difference exerts its effect? The answer, to repeat it, is all links where a difference is seen. In the wiring diagram of the brain? Yes, almost certainly. In the cellular chemistry that, in embryonic development, leads to that wiring? Of course. But also behaviour—the symphony of muscular contractions that is behaviour—this too is a perfectly respectable phenotype. Differences in building behaviour are without doubt manifestations of differences in genes. And, by the same token, the consequences of that behaviour are also entirely allowable as phenotypes of genes. What consequences? Dams, of course. And lakes, for these are consequences of dams. Differences between lakes are influenced by differences between dams, just as differences between dams are influenced by differences between behaviour patterns, which in turn are consequences of differences between genes. We may say that the characteristics of a dam, or of a lake, are true phenotypic effects of genes, using exactly the logic we use to say that the characteristics of a tail are phenotypic effects of genes.

Conventionally, biologists see the phenotypic effects of a gene as confined within the skin of the individual bearing that gene. The Beaver's Tale shows that this is unnecessary. The phenotype of a gene, in the true sense of the word, may extend outside the skin of the individual. Birds' nests are extended phenotypes. Their shape and size, their complicated funnels and tubes where these exist, all are Darwinian adaptations, and so must have evolved by the differential survival of alternative genes. Genes for building behaviour? Yes. Genes for wiring up the brain so it is good at building nests of the right shape and size? Yes. Genes for nests of the right shape and size? Yes, by the same token, yes. Nests are made of grass or sticks or mud, not bird cells. But the point is irrelevant to the question of whether differences between nests are influenced by differences between genes. If they are, nests are proper phenotypes of genes. And nest differences surely must be influenced by gene differences, for how else could they have been improved by natural selection?

Artifacts like nests and dams (and lakes) are easily understood examples of extended phenotypes. There are others where the logic is a little more... well, extended. For example, parasite genes can be said to have phenotypic expression in the bodies of their hosts. This can be true even where as in the case of cuckoos, they don't live inside their hosts. And many examples of animal communication—as when a male canary sings to a female and her ovaries grow—can be rewritten in the language of the extended phenotype. But that would take us too far from the beaver, whose tale will conclude with one final observation. Under favourable conditions the lake of a beaver can span several miles, which may make it the largest phenotype of any gene in the world. [Close quote.]

No comments: