Mind in Evolution
From The Evolving Mind, Chapters 3 and 4.
We can be very confident that our earth has supported a continuous process of the evolution of the structure of living organisms. More tentatively, we can also trace how the ‘internal’ dimensions of animals – their minds – have evolved. It is fairly clear that the capacity of animals’ minds has been limited by the size, complexity, and degree of centralization of their nervous systems, so that the evolution of physical form has constrained the evolution of mind. But has the feedback worked in the other direction too? Did mind play an active role in evolution, or was the human mind just ‘an accidental afterthought in a quirky evolutionary play’, as the biologist S.J. Gould puts it?[i]
Natural selection leads to increasing adaptation to a specific environment; it tends to promote specialization. In the mind, specialization is served by very specific inborn habits and instincts, which evolve by natural selection. But mind has an element which works in the opposite direction, particularly if individual learning and cultural traditions are possible: mind can be flexible. It can adapt an animal by coming up with behaviours that suit unexpected circumstances.
Because of its great adaptability, it turns out that mind has indeed been active in evolution. In particular, through behaviour, it can influence the process of natural selection itself. Apparently, behaviour can direct selection.
Behaviour-led Selection: An Example
Here is a plausible example of how animals’ behaviour can direct the evolutionary line their species follows.[ii] As always in biological evolution, change is very slow, or if there are fast changes, they are very rare. This means that complete examples of behaviour-led selection have not been observed occurring in nature. In addition, fossil evidence for behaviour as opposed to structure is very hard to come by. So my example is of what may have happened, not of something that definitely did happen.
The only mammals that survived the dominance of the dinosaurs were little shrew-like creatures, probably living in the undergrowth of woods and forests, and feeding by night on small animals such as insects. They had smallish brains and used their noses rather than their eyes to sense their surroundings. By 80mya, some of these insectivores had taken to the trees, giving rise to the order of primates, mammals such as monkeys, apes, and humans. Some of the earliest fossil primates were rather like bushbabies with buck-teeth, having big, forward-facing eyes, and large brains. How did the change in habitat and structure come about?
Imagine a particularly fearless early mammal running up a low branch one night. Perhaps it is being pursued by a predator; perhaps it is in pursuit of a large and juicy beetle; or perhaps it feels a vague stirring of curiosity. It finds up the branch a snug hole, and spends the dangerous daylight hours asleep there. It is safer from predators, flooding, and other dangers than its relatives, who still hide by day in burrows, under rocks, or in piles of leaves. So it teaches its own young to sleep a little above ground level. Perhaps other members of the same species imitate it, or discover the new behaviour for themselves.
Because of the extra safety, individuals with the new behaviour survive better and leave more offspring (which follow the new tradition) than conservative individuals, and scrambling into low branches every morning becomes the norm throughout the population, probably within a few dozen generations. What is more, the pioneering behaviour has opened up a new ecological niche for the species – the trees. Trees offer safer nesting holes, and also a new range of insect foods; perhaps berries and fruits, too. Our pioneering insectivore may be tempted to spend the whole time in the new habitat.
A change of environment, a new ecological niche, means new selection pressures, and this is where the conventional evolutionary mechanisms come into play. The animals are spending time in trees. However, they are not adapted for climbing but for scampering about in the leaf litter. Any mutations will be strongly selected for if they tend to develop hands that can grasp the branches, a bushy tail for balance when jumping, good binocular vision for safe climbing and finding food, and so on. So first we had a behavioural change which introduced the animal into a new environment, and then naturally selected inherited variations changed the animal’s structure. Even before the change of structure, incidentally, the new climbing behaviour could become an innate, inherited behaviour rather than one that has to be learnt afresh by each baby mammal. Natural selection sometimes ‘prefers’ instinctive to learnt behaviours, because they can be carried out more quickly and automatically, freeing the attention for other tasks.[iii], [iv]
Behaviour and Niche Change
The example of ancient insectivores discovering life in the trees showed how innovations in behaviour can open up a new environmental niche. The finding of new niches has been a vital part of animal evolution. Evolution requires not just natural selection but also a change in niche, and behaviour-led selection can be involved in niche change. If the environment alters, or if some individuals stray into a new environment, behavioural changes are very likely to play a role in helping them to survive. For example, if our primitive insectivores were plunged into a series of severe winters, behavioural innovations in making cosier nests might well prevent the extinction of the population for long enough for thicker and thicker fur to arise by the natural selection of inherited variations in fur length.
The potential for new behaviours is also, presumably, often important when an animal is faced with changes in local habitat and geography, food supply, predators, or competitors. If the insectivore lives mainly on slugs but the slugs die out, it must turn to another food or starve to death. (We must not forget here an even more direct way in which animal choice influences evolution. That is the selection of a preferred mate, whose genes will mix with the suitor’s genes to contribute to the next generation.)
New species are thought to arise usually by the splitting of an existing species, so we need some mechanism which isolates the population from any remaining members of the species still following the old life-style, so that the new and old groups do not interbreed. Some isolation mechanisms themselves involve changes in behaviour, so that behaviour-led isolation should be added to behaviour-led selection as a factor in evolution.
For evolution to proceed, reproductive isolation and niche change must occur together. In animals that can change their behaviour, new behaviours are likely to be the commonest way for that to come about. As the biologist C.H. Waddington observed:
Animals … live in a highly heterogeneous ‘ambience’, from which they themselves select the particular habitat in which their life will be passed. Thus the animal by its behaviour contributes in a most important way to determining the nature and intensity of selection pressures which will be exerted on it.[v]
It is through behaviour-led selection that animals may affect the future course of the evolution of their own species. Individual choices and preferences ensure that evolution does more than merely grope randomly into new areas. By way of recapitulation, here is how the philosopher Karl Popper summarizes this view:
At first sight Darwinism … does not seem to attribute any evolutionary effect to the adaptive behavioural innovations of the individual organism. This impression, however, is superficial. Every behavioural innovation by the individual organism changes the relation between that organism and its environment: it amounts to the adoption of or even to the creation by the organism of a new ecological niche. But a new ecological niche means a new set of selection pressures, selecting for the chosen niche. Thus the organism, by its actions and preferences, partly selects the selection pressures which will act upon it and its descendants. Thus it may actively influence the course which evolution will adopt. The adoption of a new way of acting … is like breaking a new evolutionary path.[vi]
[i] Gould, S.J., Wonderful Life, Penguin, Harmondsworth 1991, 233.
[ii] A similar example was given by H.W. Conn in 1900, quoted in Hardy, A., The Living Stream, Collins 1965, 179.
[iii] Reid, R.G.B., Evolutionary Theory: The Unfinished Synthesis, Croom Helm 1985, 244; Bateson, P., ‘The Active Role of Behaviour in Evolution’ in M.-W. Ho and S.W. Fox, Evolutionary Processes and Metaphors, 191–207, Wiley 1988, p6 of preprint. But John Maynard Smith (‘The Birth of Sociobiology’, in New Scientist 26 September 1985, 50) doubts that the behaviours themselves would become genetically fixed.
[iv] Behaviour-led selection is a specific form of the ‘organic selection’ independently proposed by C. Lloyd Morgan in Britain and J. Mark Baldwin and H.F. Osborne in America. The history and status of the idea of organic selection is reviewed by R G B Reid, Evolutionary Theory, (Croom Helm 1985, 239–247). It is also discussed by (among others) the following biologists: Julian Huxley (Evolution, the Modern Synthesis, Allen & Unwin 1942, 523), G. Simpson (‘The Baldwin Effect’, in Evolution, vol 7 (1953), 110–117), E. Mayr (Animal Species and Evolution, Harvard University Press 1963, 95, 106–7, 604–5), A. Hardy (The Living Stream, op cit, 154–5, 162–207. Hardy gives a number of other references to writing on organic selection in The Living Stream and Darwin and the Spirit of Man (Collins 1984)), C.H. Waddington (The Evolution of an Evolutionist, University Press, Edinburgh 1975, 89, 279–281), J. Piaget (Behaviour and Evolution, Routledge & Kegan Paul 1979 (1st edn 1976), xiv–xv, 15–45, 134–145), Patrick Bateson, (‘The Active Role of Behaviour in Evolution’, in M.-W. Ho and S.W. Fox, op cit, 191–207). The philosopher of science Karl Popper is an enthusiastic proponent of behaviour-led selection as the source of direction in evolution. (Objective Knowledge, Clarendon, Oxford 1972, Chapter 7, and Unended Quest, Collins 1976, 173–80.) Interestingly, standard university textbooks on biology or evolution rarely mention organic selection or the Baldwin Effect (as it is also known), and negligible experimental work has been done on its behavioural aspect.
[v] Waddington, ‘Evolutionary Systems, Animal and Human’, in Nature, vol 183, 1634–8. Waddington included the selection of niches by behaviour in his ‘exploitive system’ (‘Evolutionary Adaptation’, S. Tax (ed), The Evolution of Life (Chicago 1960)).
[vi] Popper, Unended Quest, op cit, 180 (Popper’s emphasis).