The importance of moving from evolution as abstraction to particular history

Given the diversity of philosophical conclusions that can be drawn from natural selection when considered in abstract terms, it is vital that actual data from natural history (and physics where applicable) be used to help us narrow the options. It is no longer possible for informed commentators to characterise evolution as pure contingency or deterministically convergent upon a single end-point. The question has instead become: to what degree is evolution on Earth (and elsewhere in the universe) constrained and which of the four views above is closest to the actual state of affairs?

Thankfully, recent work in palaeontology and palaeobiology has made considerable headway towards resolving this debate. According to Cambridge palaeobiologist Simon Conway Morris, the constraints may be very great indeed, which lends support to the ‘universal biology’ view. In his recent book Life’s Solution: Inevitable Humans in a Lonely Universe he explores which aspects of the history of terrestrial biology appear to be constrained by universal laws and which may be due to chance. Interestingly, rather than argue that one or the other factor dominates, he suggests they both do.

Conway Morris supports his argument in two ways: by showing how terrestrial DNA-based biochemistry is demonstrably superior to alternatives, and by showing how different organisms have converged upon the same solution when independently facing similar problems. One particularly interesting case is chlorophyll. According to Conway Morris, it is difficult to conceive of an alternative mechanism for photosynthesis. In fact, terrestrial evolution has converged upon chlorophyll even though it is poorly optimised for converting the particular wavelengths of light received from our Sun. This leads him to wonder if life on planets orbiting different kinds of stars would also converge on chlorophyll.Importantly for our next discussion, he considers intelligence to be universally adaptive, and so an inevitable outcome of natural selection given sufficient time and resources. In fact, if there are intelligent extra-terrestrials he expects them to be pseudo-mammalian bipeds with stereo camera eyes.

However, there is another side to the story. While many of the basic building blocks of life are plentiful, the chances of there being a hospitable planetary environment in which life can begin and flourish, are remote in the extreme. Here there are no known laws that can influence the likelihood. Our Earth owes its biology-enabling nature to a long list of accidents which make Earth-like planets unlikely elsewhere. This leads Conway Morris to guess that life is not common, i.e. it is a ‘lonely universe.’

Conway Morris’s work is of great help as we try to add flesh to the abstract bones of natural selection and determine the degree of constraint it is under. However, it is still early in the debate. Ironically, the data driving Conway Morris’s view comes mainly from the Burgess Shale fossils in British Columbia and the K-T extinction. This is the same data that led Gould to the opposite conclusion. Gould emphasised the large number of species that did not make it through the K-T extinction, and concluded that life on Earth today is due to our ancestor’s lucky survival through this catastrophe. Conway Morris, however, believes that the drive to convergent solutions is powerful enough to overwhelm events even as disruptive as the K-T extinction. Where Gould consider the K-T impact one (among many) contingent causes of the rise of the mammals, Conway Morris suggests it only brought it forward by some thirty million year” and “although there may be a billion potential pathways for evolution to follow from the Cambrian explosion, in fact the real range of possibilities and hence expected end results appear to be much more restricted.”

While there is a need for further research and debate it looks as though the view of biological history as essentially a capricious random walk with arbitrary end-points may be headed for extinction. If Conway Morris is correct and evolution is highly constrained by universal laws this finding will mark an important milestone in the philosophy of biology and philosophy of science in general.

If there is evidence for a ‘universal biology’ it will link evolution with the ‘fine-tuning’ and Anthropic Principle debates in astrophysics. It was recognised several decades ago that a number of physical constants have values that allow for life where other configurations of constants would preclude it. Thus far it has not been possible to argue persuasively that the laws of physics give rise to life, but by coupling cosmic fine-tuning with Conway Morris’s work, this kind or argument is now a possibility. Importantly, there is currently no ‘scientific’ explanation for why the constants have these particular life-related values. Speculations vary between postulating an infinity of universes where the values are randomised by some as yet unknown process, and the admission that the values are simply ‘given.’

New data may yet point in the opposite direction and so support Monod’s view, but it is now conceivable that scientific data could come to support the view that the universe is fine-tuned for intelligent life. The debate over convergence has added urgency to the closely related question of directionality in evolution, to which we now turn.

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