"What do we really mean by the phenotypic effect of a gene? A smattering of molecular biology may suggest one kind of answer. Each gene codes for the synthesis of one protein chain. In a proximal sense that protein is its phenotypic effect. More distal effects like eye colour or behaviour are, in their turn, effects of the protein functioning as an enzyme. Such a simple account does not, however, bear much searching analysis. The “effect” of any would-be cause can be given meaning only in terms of a comparison, even if only an implied comparison, with at least one alternative cause. It is strictly incomplete to speak of blue eyes as “the effect” of a given gene G1. If we say such a thing, we really imply the potential existence of at least one alternative allele, call it G2, and at least one alternative phenotype, P2, in this case, say, brown eyes. Implicitly we are making a statement about a relation between a pair of genes {G1, G2} and a pair of distinguishable phenotypes {P1, P2}, in an environment which either is constant or varies in a non-systematic way so that its contribution randomizes out. “Environment”, in that last clause, is taken to include all the genes at other loci that must be present in order for P1 or P2 to be expressed. Our statement is that there is a statistical tendency for individuals with G1 to be more likely than individuals with G2 to show P1 (rather than P2). Of course there is no need to demand that P1 should always be associated with G1, nor that G1 should always lead to P1: in the real world outside logic textbooks, the simple concepts of “necessary” and “sufficient” must usually be replaced by statistical equivalents.
Such an insistence that phenotypes are not caused by genes, but only phenotypic differences caused by gene differences (Jensen 1961; Hinde 1975) may seem to weaken the concept of genetic determination to the point where it ceases to be interesting. This is far from the case, at least if the subject of our interest is natural selection, because natural selection too is concerned with differences (Chapter 2). Natural selection is the process by which some alleles out-propagate their alternatives, and the instruments by which they {196} achieve this are their phenotypic effects. It follows that phenotypic effects can always be thought of as relative to alternative phenotypic effects.
It is customary to speak as if differences always mean differences between individual bodies or other discrete “vehicles”. The purpose of the next three chapters is to show that we can emancipate the concept of the phenotypic difference from that of the discrete vehicle altogether, and this is the meaning of the title “extended phenotype”. I shall show that the ordinary logic of genetic terminology leads inevitably to the conclusion that genes can be said to have extended phenotypic effects, effects which need not be expressed at the level of any particular vehicle."
I was much interested by these very general matters of selection, but took most of my ideas from David L Hull (replicators and interactors) rather than Dawkins.
18 March 2013 at 17:34
Matthew C. said...
"A pretty big set of necessary assumptions...
A pretty big class of problems which are routinely ignored."
Ah, but it has to be. Or otherwise, God is real, therefore life has purpose, therefore we are NOT to rut around like the beasts of the field and there are actual expectations on us.
18 March 2013 at 18:38
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Natural selection is about incremental modification of already-existing forms or traits.
There is no problem about this happening - I mean that traits such as body size and structure or behaviours and abilities are modified by natural selection - obviously they sometimes are modified by selection (whether natural or artificial).
But there are difficulties which an explanation using natural selection must acknowledge.
One is this: How do we know what are the forms which natural selection modifies?
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From the open-ended complexity of an organism - the limitless ways in which we might analyze its structure, behaviour and everything about it - how do we decide what are its 'traits' in order that we can potentially explain how they have evolved?
What is the objective evidence that a hand, or a wing, or a particular patten of food seeking behaviour is a trait? - something unitary, cohesive, which can be explained?
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It seems 'obvious' to us that a hand is a trait - but that obviousness may be denied, or it may be an artifact of our own evolution. To an amoeba a hand is not a trait. If somebody doubts that a hand is a trait, how can they be convinced?
This is the deepest metaphysical problem of using natural selection as an explanation - the problem of explaining how we know what it is that has to be explained.
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This problem has only one answer: that the knowledge of what has to be explained, if it is to be valid, must come from outside of the discourse of natural selection: thus natural selection cannot be an ultimate explanation.
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Natural selection operates within the discourse that tells us what needs to be explained - it just does - so the discourse that tells us what needs to be explained is more ultimate than natural selection.
Consequently, natural selection must be (and I mean must be - this is logically entailed) just one way of explaining what it is that needs to be explained.
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Consequently, in relation to discussing the status of natural selection (the philosophical meta-subject which is evaluating the validity of natural selection as a discourse, rather than the specific instances of proposed natural selection - which are just normal science) the discourse that must be made explicit is that which describes what is a species, what is an organism, what is a trait.
How seldom this is addressed by those who argue for the ultimate and universal validity of natural selection...
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(Obviously that meta-discourse which tells us what natural selection validly does, cannot itself use the explanation of natural selection! Natural selection cannot be used to validate natural selection; when the validity of natural selection is the matter being evaluated!)
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From this we can infer that natural selection is based on assumptions concerning the nature of reality - that there are species (or some equivalent of organisms related by descent), that there are organisms as basic units of explanation, and that organisms may be analyzed into traits each of which can evolve by natural selection (with some significant degree of autonomy), and that we can recognize all these - that we humans can look-upon the natural world and validly perceive that there are such entities as species, organisms and traits, and we recognize what they are individually and specifically.
A pretty big set of necessary assumptions...
A pretty big class of problems which are routinely ignored.
"What does natural selection operate upon?"
3 Comments -
You raise an important point that tends to go unnoticed.
Richard Dawkins mentions this issue in his book The Extended Phenotype:
http://scilib.narod.ru/Biology/Dawkins/Phenotype/Dawkins_R.-Extended_Phenotype.html#11
"What do we really mean by the phenotypic effect of a gene? A smattering of molecular biology may suggest one kind of answer. Each gene codes for the synthesis of one protein chain. In a proximal sense that protein is its phenotypic effect. More distal effects like eye colour or behaviour are, in their turn, effects of the protein functioning as an enzyme. Such a simple account does not, however, bear much searching analysis. The “effect” of any would-be cause can be given meaning only in terms of a comparison, even if only an implied comparison, with at least one alternative cause. It is strictly incomplete to speak of blue eyes as “the effect” of a given gene G1. If we say such a thing, we really imply the potential existence of at least one alternative allele, call it G2, and at least one alternative phenotype, P2, in this case, say, brown eyes. Implicitly we are making a statement about a relation between a pair of genes {G1, G2} and a pair of distinguishable phenotypes {P1, P2}, in an environment which either is constant or varies in a non-systematic way so that its contribution randomizes out. “Environment”, in that last clause, is taken to include all the genes at other loci that must be present in order for P1 or P2 to be expressed. Our statement is that there is a statistical tendency for individuals with G1 to be more likely than individuals with G2 to show P1 (rather than P2). Of course there is no need to demand that P1 should always be associated with G1, nor that G1 should always lead to P1: in the real world outside logic textbooks, the simple concepts of “necessary” and “sufficient” must usually be replaced by statistical equivalents.
Such an insistence that phenotypes are not caused by genes, but only phenotypic differences caused by gene differences (Jensen 1961; Hinde 1975) may seem to weaken the concept of genetic determination to the point where it ceases to be interesting. This is far from the case, at least if the subject of our interest is natural selection, because natural selection too is concerned with differences (Chapter 2). Natural selection is the process by which some alleles out-propagate their alternatives, and the instruments by which they {196} achieve this are their phenotypic effects. It follows that phenotypic effects can always be thought of as relative to alternative phenotypic effects.
It is customary to speak as if differences always mean differences between individual bodies or other discrete “vehicles”. The purpose of the next three chapters is to show that we can emancipate the concept of the phenotypic difference from that of the discrete vehicle altogether, and this is the meaning of the title “extended phenotype”. I shall show that the ordinary logic of genetic terminology leads inevitably to the conclusion that genes can be said to have extended phenotypic effects, effects which need not be expressed at the level of any particular vehicle."
18 March 2013 at 17:18
You may be interested by the Appendix on Systems Theory to my book from a decade ago (before I was a Christian and a Reactionary!)
http://www.hedweb.com/bgcharlton/modernization-imperative.html
I was much interested by these very general matters of selection, but took most of my ideas from David L Hull (replicators and interactors) rather than Dawkins.
18 March 2013 at 17:34
"A pretty big set of necessary assumptions...
A pretty big class of problems which are routinely ignored."
Ah, but it has to be. Or otherwise, God is real, therefore life has purpose, therefore we are NOT to rut around like the beasts of the field and there are actual expectations on us.
18 March 2013 at 18:38