DEVELOPMENTAL SYSTEMS THEORY [Type the document subtitle]
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What is developmental systems theory?1 Developmental systems theory is an answer in the units of selection debate. The question, somewhat simplified, is: what is the unit of selection in evolution. In other words, what is it exactly that is being selected for and against, in natural selection? The layman’s answer is that the unit of selection is the organism; the animal is selected for or against. Dawkins, in his influential The Selfish Gene, argued instead that the genome inside the organism is the unit that is acted upon during selection. Developmental systems theory broadens the selection unit to include any of the developmental resources that are replicated by later generations. For example, orthodoxy would not consider a rabbit’s burrow to be part of the unit of selection. Developmental systems would deny this. The burrow plays a part in the development of the rabbit, influences later generations and is also replicated in later generations by younger rabbits making new burrows. It is thus similar enough to the gene to be considered as part of the selection unit. The fundamental point made by premier DST proponent Susan Oyama is that the information in the life cycle of an individual is itself a product of becoming, of ontogenesis2. This is all-important for DST. The information passed between generations is not given a unique status that excludes it from evolutionary explanation. It is instead recognised that beginning the evolutionary story with a central focus on DNA is arbitrary. After all, DNA itself neither completely preexisted evolution, nor did it arise from random disorder 3. Bearing this is mind, one cannot avoid the conclusion that DNA and the gene are also products of evolution. DST rejects classifying phenotypic causes into the traditional groups of genetic and environmental. This is because they have a more holistic view: genetic and environmental factors are just imaginary subsets. What is really the case is that genes and the environment are both parts of the developmental system that most organisms find themselves in. The division of this system into the groups mentioned is arbitrary because they do not differ in the way they would need to for the distinction to be of use. I will use DST in this essay to refer both to Developmental Systems Theory and to Developmental Systems Theorists. Hopefully no confusion will arise. If only someone more simple minded than Susan Oyama was given the task of naming the theory perhaps this wouldn’t be needed… 2 Griffiths & Gray, 1994, p. 285 3 Oyama, 1985, p. 3 1
Development Systems Theory – Ben Dempster
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For example, it is often cited in defence of the dichotomy that genes differ greatly from environmental factors because one is the cause of ‘innate’ traits and the other, merely ‘acquired’ ones. This distinction is challenged by DST too. Experiments supposedly demonstrating the distinction are question begging to the extreme. The aim of such experiments is to hold environmental factors constant while altering the genome; the result is an affected phenotype which is then considered evidence that genetic causes are to be distinguished. However, this is merely a function of the method of experimentation used. If the accepted view had been that genetic and environmental factors were two sides of the same coin, the isolation experiment would have run differently. An experimenter could isolate any number of the multitude of causes and end up with a different dichotomy every time. As DST constantly points out to the rest of the biology world, arbitrariness is rampant. By a similar method, DST renounces the traditional separation of biological and cultural mechanisms. They argue that cultural inheritance and influence is just another kind of biological influence. Once again the division is attacked by highlighting similarities between aspects of biology and culture. Cultural and biological inheritance are not as different as one might initially believe. Culture passes itself down through the generations via many methods: verbal transmission, such as teaching, information vaults (libraries, the internet) and imitative behaviour are all methods used to sustain cultural information over time. The same is true in biological evolution. Objectors propose smaller generation times and horizontal inheritance as points of difference between cultural and biological evolution. However, generation times are only small in cultural terms if we assume the same taxonomic system should be used of human cultures and biological systems. Such an assumption should be rejected. Horizontal inheritance is no stranger to biological evolution either; processes like plasmid exchange and hybribization attest to this 4. Furthermore, cultural mechanisms have been excluded from biological consideration for so long because of the misguided assumption that culture is a largely human enterprise. Humans, in the modern scientific world, like to consider themselves outside of the natural selection. A large part of this is due to the intricate, complex culture we have – it gives the impression that we have moved on from the animal world. Of course, this is far from the truth, study reveals many primates have at least as much interaction as we do that must qualify as culture. Because humans and other animals have what can be classed as a culture, we are wrong to distinguish it from other biological events along these lines. 4
Griffiths & Gray, 1994, p. 302
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4|Page DST also rejects as false the interactor / replicator distinction. Their argument for this claim rests on re-evaluating the Weismannian dogma that DNA is the cause of both genetic and somatic (i.e. the organism) material. If this Weismannian view is correct, we have obvious categories for interactors and replicators; the somatic individual is the interactor, and the DNA is the replicator. If, however, Weismann’s picture is false, one can argue that such division is again arbitrary, that it doesn’t correctly carve up the natural world. A few counterexamples are enough to show that this picture is recklessly oversimplified. Consider the choices that one’s parents made in deciding to be together, and, eventually, the decision to mate. This can hardly be said to be a direct effect of DNA, this choosing, unless we are willing to equate the ‘Gene’s Eye View’ with genetic determinism. So, one must ask, in what sense is the DNA the replicator and the individual the interactor here? The interactions that the individual is involved in have a direct relation to the replication of DNA. Without certain interactions, there would be no replication. With this is mind, it is difficult to see how the interactor / replicator distinction distinguishes anything in reality. Another method of persuasion DST has to convince us replication / interaction distinctions are groundless is a broadening of the notion of inheritance. If we believe, as gene selectionism does, that DNA is the only inheritance mechanism, it is a short step to conflating this singular inheritance with the existence of a specialised replicator. If, on the other hand, DST can show us inheritance has multiple methods, the replicator / interactor distinction becomes too difficult to make out. This is because without a unique system of inheritance, replicators can be too varied in nature for the simplified distinction to make sense. The existence of multiple inheritance systems is exactly what DST demonstrates. Epigenetic inheritance factors are a perfect example. Not just DNA is transmitted during the process of sexual reproduction, but also many things such as DNA methylation systems as well as information from the mitochondria 5. Surely this phenomena is better explained by citing alternative inheritance mechanisms than by classing the mitochondrial information as part of the ‘stable’ environment? The new approach that DST takes to evolution requires a restatement on many of the issues evolutionary theory usually discusses. Because what is considered important for evolution in the DST picture is the interactions between developmental resources, the unit of selection becomes the life cycle as a whole, not any specific part of it. How can a demarcation be made between one life cycle and the next? Every life cycle begins with the same kinds of developmental resources as the previous 5
Sterelny & Griffiths, 1999, p. 95
Development Systems Theory – Ben Dempster
5|Page generation. The individual is reconstructed from comparatively basic ingredients in successive generations. This, in turn, means the catch phrase for evolution is not survival of the fittest, where fitness is defined as fittedness to a stable environment. Instead, it is differential replication of different life cycles. An effective evolutionary product is one that has appropriately structured resources present in each generation. Competition in evolution is characterised by DST as the commonly occurring situation where certain resources are part of multiple developmental systems. Assumedly, these resources are limited, and differential ability to secure access to such resources is linked to the difference in fitness on the old evolution model.
Is developmental systems theory. a good solution to the units of selection problem? The traditional method for determining the worth of DST in the face of the unit of selection debate is to contrast it with its big rival, the Gene’s Eye View. This theory attempts to entrench the genetic / environmental dichotomy by giving genetic factors more importance. If this succeeds, the situation for DST is obvious: if genetic factors can be distinguished as more important, the distinction between genetic and all other factors will not be so arbitrary. One common tactic is to contend that genetic replication is more ‘direct’ than other forms. A clear example of this is the fidelity with which genetic codes are transmitted to later generations. But is genetic replication really so direct? This must rest on the immediacy of the process that takes place when DNA is transmitted. The most recent studies suggest that such directness is simply non-existent in genetics. The DNA to protein process is very complex. The messenger of DNA, RNA, is what assembles the amino acids into protein 6. This in itself is substantial: DNA is far from direct in making somatic material.Furthermore, it is common for the RNA construction to 6
Sterelny, 1999, p. 103
Development Systems Theory – Ben Dempster
6|Page be abnormal, or ‘wrong’7. Because of this, it is not true that DNA is faithfully represented by its RNA messenger. In turn, we cannot call DNA replication direct. With regards the fidelity of DNA copying, evidence can be offered to show other copying mechanisms are equally faithful. The style and shape of a rabbit’s burrow can be passed from parent to offspring if that offspring finds a new habitat and reproduces another similar burrow. The similarity of rabbit burrows shows them to be an excellent example of h-fidelity replication. It has also been claimed, in defence of gene selectionism, that genetic factors have greater importance because they have more specific effects. Isolation experiments, which hold environmental factors constant, supposedly show that the existence of different genes translates into different specific traits. Thus, if one has gene X, one is almost certain to get the genetic disease X1. On the other hand, environmental factors are purported to have a more vague role. If one suffers from bad nutrition there are a great number of phenotypic outcomes, such as weakness, lack of growth and less efficient immune system. So, the gene selectionist argument goes, gene X has a direct outcome, whereas environmental factors have unspecific effects. Unfortunately, the difference between genetic and environmental factors cited above is actually already a product of the objectionable dichotomy. Note that in the imaginary isolation experiment above, all genetic factors but one are excluded. The same is not true of the environmental factors when discussing nutrition. Nutrition is not just one environmental factor that can be signified all at once. Instead, whether or not an individual has bad nutrition depends on a great number of environmental factors. Hence, all the non-specific effects show is that the cause too is non-specific; something we would consider obvious when considering the number of developmental resources that contribute to nutrition. Moreover it is begging the question to say genetic effects are specific and environmental effects are not when the experimental set-up already presumes all environmental causes can be classed as one. Consider how ridiculous the ploy seems when inverted: genetic causes are non-specific because a person’s DNA (as one unit) can produce so many different phenotypes. A further attempt to discredit DST by imparting special significance to the gene involves the assertion that DNA is the information in evolution. This ploy can accept that environmental causes are important; they are necessary and sufficient conditions for the ‘decoding’ of the information stored in the genome. The method makes the genome the most important factor, though, because without the information stored within it, the individual would never eventuate. 7
Sterelny, 1999, p. 103
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What must first be emphasised in a DST response is that the developmental systems view is not trying to subvert the genome as a vital part of the biological process. The same cannot be said for naïve followers of Dawkins with regards the environment. With this in mind, DST can agree that whatever it is the genome has is vital for development, without having to accept the further (and much bolder) claim that genes have information but the environment doesn’t. There are two ways the conception of information can be taken. One is inappropriate for biology and the other squares much better with DST than with gene selectionism. The first is the semantic or intentional view of information. Information, on this assessment, is the product of some intentional system, and contains semantic information about that system. A conversation is a good model for such a system. It is the product of the intentions of the humans involved in the conversation, and the words have semantic content. Thus, what gets spoken in a conversation is information. The difficulty with importing this view into biology is that is near impossible to give a coherent account of what one could mean by intention. One only needs to sketch a few of the problems to see it is a doomed suggestion. Who is the intentional agent in biology? If one’s answer is God, one can only claim in response that this rejects ontological parsimony (Razor style). By using God to justify biology, one must in turn justify the existence of God, certainly no straightforward task. Other possible candidates for the intentional agent in the biological system are notoriously hard to come by. In what sense can we say evolutionary systems have intention, other than by claiming, with Dawkins, that individuals are survival machines? And can one reasonably class the survival instincts of biological individuals as intentional? I suggest one cannot. An individual survives if its development goes well according to the available resources. This survival does not depend on any intention of the individual itself, otherwise lower animals, which we do not consider intentional agents, wouldn’t be part of evolution. The other way to understand information is as like a physical property. This is known as mathematical information theory. This theory suggests that there is an information flow between two systems as long as there is covariance between them. Thus, system A and system B contain information about each other as long as one can correctly infer anything about B from knowledge of A, or vice versa. On this account, any covariance is called information, regardless of the relevance that the information has. Hence, radio static is information about the
Development Systems Theory – Ben Dempster
8|Page radio (informing me it is receiving power) – even if it is useless to me most of the time. An important consequence of the mathematical theory of information is that channels and sources can be switched around gestalt style. So, if we considered a message coming via a Morse code machine, we could call the sender a source and the wire a channel and vice versa. The sender is a source of information about whatever message she wants to send. The wire is a source of information about the sender: if the wire is active, I know there is someone using the machine at the other end. This way of seeing information has a big impact on the units of selection debate. If the information in evolution is from a non-intentional system, which seems the more plausible option, mathematical information rules apply to it. This means the genome can be seen as the source and the environment as the channel, but this is mere stipulation; the distinction does not exist in reality. Any covariance at all between two systems counts as an information flow. So, trees are a source of information about beavers just as beaver DNA is a source. One can distinguish between sources, but there is no reason to think that genome supremacy must be privileged in the system. The upshot is that DST stacks up favourably when compared to the more naïve strains of the Gene’s Eye View. DST certainly answers some biological mysteries better than alternatives. Oyama’s ontogeny of information conception is correct to emphasise that DNA and genetic inheritance are themselves a product of evolution. These prior processes must have had non-genetic bases, hence genetic inheritance is neither pervasive nor unique. Furthermore, the ‘standard environment’ which is assumed in the background of isolation experiments simply does not exist. Dawkins claims causality is mostly statistical for biology8. Yet, one cannot interpret ‘standard’ in the statistical sense, otherwise it will make little sense to talk of apple seeds ‘coding’ for apple trees, given that only a small proportion of seeds actually achieves treehood. If such a standard is non-existent, we cannot assume there is a distinct difference between stable environmental factors on one hand and information bearing genetic ones on the other. On the whole, therefore, I contend DST is a good answer to the units of selection debate. Gene selectionism as an alternative is unappealing, at least in its unsophisticated version. Some suggest that the genetics / environment dichotomy may be arbitrary but still useful9. Multiple replicator theory suggests that the replicator / interactor distinction is still a handy one. However, given 8 9
Dawkins, 1982, p. 11 Sterelny (unpublished)
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9|Page that these theorists allow that an animal can be considered as both replicator and interactor, the distinction easily breaks down 10. The end result here is that DST is a fresh response to the selection debate that benefits from a lack of arbitrary assumptions about the genome.
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Sterelny, Smith & Dickerson, 1996, p. 399
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Bibliography Bateson, P.P.G. 1976. “Specificity and the Origins of Behaviour,” Advances in the Study of Behaviour, 6, pp. 1-20 Dawkins, R. 1982. The Extended Phenotype, Oxford: Oxford University Press Griffiths, P.E. and Gray, R.D. 1994. “Developmental Systems and Evolutionary Explanation,” The Journal of Philosophy, 91 (6), pp. 277-304 Oyama, S. 1985. The Ontogeny of Information, New York: Cambridge University Press Sterelny, K. (unpublished manuscript) “Niche Construction, Developmental Systems and The Extended Replicator” Sterelny, K. and Griffiths, P.E. 1999. Sex and Death: an Introduction to Philosophy of Biology, Chicago: University of Chicago Press Sterelny, K., Smith, K. and Dickerson, M. 1996. “The Extended Replicator,” Biology and Philosophy, 11 (3), pp. 377-403
Development Systems Theory – Ben Dempster