Naturalist Alfred Russel Wallace died in November 1913. James Le Fanu looks at his legacy and its impact on evolutionary theory.
When invited to contribute to a conference on evolution held, appropriately enough, in the Galapagos Islands, I seized the opportunity to fulfil a long-held ambition to swim with turtles.
The setting was magical — a white beach littered with sea lions nursing their young, on the nearby rocks battalions of dragon-like marine iguanas basked in the early morning sunshine, a pair of magnificent frigate birds soared aloft like piratical pterodactyls, while tiny bright yellow warblers flitted through the undergrowth. Then plunging into the sea, there they were — two large turtles gliding effortlessly through the water seemingly indifferent to my presence. It was as though I had strayed into some other strange, timeless and dreamlike world.
Later that morning, back in the conference hall, speakers presented their papers on recent developments on evolutionary biology elaborating on that insightful explanation by the Galapagos’s most famous visitor, Charles Darwin for the presence of so many closely related species of birds and reptiles scattered throughout the islands.
The finch
The Galapagos is home to 14 different species of finch, each with its own distinctive plumage. But it was the variation in their beaks, reflecting the difference in their feeding habits, that suggested they might be descended from a common ancestor — whether nutcracker shaped for eating seeds, curved for probing flowers or long and slender for catching insects. ‘Seeing this gradation and diversity in this small closely related group of birds’, Darwin wrote, ‘one might readily fancy an original species had been modified for different ends.’
The proposed mechanism of natural selection acting on random genetic mutations certainly provides a plausible explanation for those variations in beak morphology. It is much less certain, however, whether it also accounts for the profundities of anatomical form — exemplified, for example, by those green turtles and their close relatives, the famed giant Galapagos tortoise. The protection against potential predators of their heavy inflexible shells has ensured their survival for an astonishing 250 million years during which they would have witnessed the massive geological upheavals that formed the continents and oceans.
Major redesign?
But those shells also have several drawbacks, readily overlooked if obvious on reflection. They are formed by the fusion of their bony parts, including the external limb girdles of scapula and pelvis from which the fore and hind limbs are suspended. Thus, to retain their mobility, they had to undergo a major ‘redesign’ where the limbs arise from within the body cavity — as though, if it could be imagined, our arms were attached to the inner wall of the ribcage and protruded outwards on either side of the neck. No other creatures do this.
Nor is that all, for enclosed within that bony carapace neither turtle nor tortoise could breath, as do all other reptiles and mammals, by the movement of the chest wall drawing air in and out of the lungs. And so, again uniquely, they possess two novel muscles that act a like bellows; the retraction of one expanding the lungs sucking in air and the contraction of the other expelling it.
Mating
The further constraint imposed by that bony shell is the seemingly insuperable impediment to mating when both male and female are wearing, as it were, an inflexible sheet of armour. And so here the male possesses a concealed phallus which, when the need arises, massively extends like a hydraulic cylinder to half the length of his body with which he ‘services’ the female partner beneath him.
Challenge to evolutionary theory
The contribution of the iconic inhabitants of the Galapagos Islands to our understanding of biology is thus highly ambiguous. Those finches’ beaks have come to symbolise in the public imagination the power of science to explain the wondrous diversity of form and attributes of the living world. But that might seem a trivial fact when set against the challenge to current evolutionary theories posed by those extraordinary unique anatomical innovations without which neither Galapagos turtle nor tortoise could have happened — let alone persist unchanged throughout those almost unimaginable eons of time.
Those attending conferences on evolution tend not to dwell on such ‘difficulties’. They are, however, scarcely novel, having been frequently and forcibly expressed by no less than the co-discoverer of the theory of natural selection himself, the brilliant Victorian naturalist and explorer, Alfred Russel Wallace. His story is familiar enough. Towards the end of his epic eight-year expedition through the Malayan archipelago, Wallace had an epiphanous insight when struck down by a bout of malaria, that the combination of minor variations in form and the struggle for survival could give rise to new species. This led him to write a scientific paper on this theme which he sent to Darwin with whom he regularly corresponded. Darwin, fearful that the all-important priority would go to Wallace (‘and all my originality will be smashed’) arranged for it to be read alongside a letter of his own describing the same theory at a meeting of the learned Linnean Society.
An ‘organising life principle’
2013 marks the 100th anniversary of Wallace’s death, prompting renewed interest in his subsequent apostasy — as it is commonly portrayed. His arguments, as set out in his magnum opus The World of Life published in 1910, have a surprisingly familiar ring. The first concerns the enigma of the origins of the earliest forms of life whose properties of ‘nutrition, growth and reproduction’, Wallace argued, defy any suggestion they could be the ‘mere consequence of complex chemical interactions’. Then he insists that biological marvels such as the strength and lightness of a bird’s feather or the metamorphosis from larvae to butterflies presuppose some ‘organising life principle’. He is not convinced by evolutionary explanations for the phenomenon of colour in plants and animals: ‘Why should the homely gorse be clothed in golden raiment and the prickly cactus adorned with crimson bells?’ And, finally, there is the excep-tionality of man whose mental faculties set him too far apart from the rest of creation to be ‘explained away’ as the consequence of a known materialist process. Rather, Wallace maintained, it is necessary to infer a Directive Mind and Ultimate Purpose behind appearances. It is interesting to speculate how different common perceptions might be were the biology curriculum to encompass not just those variations in beak morphology of the Galapagos finches, but also Wallace’s evolutionary metaphysics.
