We generally chart the start of modern science as we know it from Francis Bacon, one of the major English figures of the Renaissance period. It is Bacon, writing in the first decades of the 17th century, who is usually credited with spelling out the principles of empirical science and the role that experiments should play in hypothesis testing. The great irony, however, is that, despite his enormous influence on the later generations of scientists from Newton onwards, Bacon himself never touched a test tube. He simply set the scene from his armchair and told the scientists how they ought to proceed.
In fact, the real credit for establishing genuine empirical science based on careful observation and the deduction of causal explanations belongs to Aristotle, that paragon of genius who established the so-called Peripatetic school at the Lyceum in Athens almost 2000 years before Francis Bacon was even a gleam in his mother’s eye. Originally a pupil of Plato, Aristotle broke with Plato’s idealism when he spent a dozen years on various Aegean islands after his master’s death. There, he developed his own empirical approach to philosophy.
Yet Aristotle has always had something of a bad reputation among both scientists and philosophers – mainly thanks to Bacon, who railed against the mind-numbing influence Aristotle had on the philosopher-theologians of the medieval period. For Bacon, Aristotle was the big baddy who was single-handedly responsible for all the worst habits of the intellectual trivialisers of the medieval period. But if Bacon genuinely thought this, it must have been because he never bothered to read Aristotle at first hand. For even the most casual perusal of Aristotle’s writings reveals a formidable intellect spanning everything from moral and political theory to logic, physics and biology. And it is in his biology that Aristotle’s genius really shines through. Unlike his physics, Aristotle’s biology is marked by an extreme emphasis on observation. The ancient Greeks regarded unencumbered thought as the highest form of existence (hence their enthusiasm for geometry). As far as they were concerned, messing about with the real world was something to which even consenting adults ought not admit. Soothsayers digging around in the entrails of sheep to predict the future was about as much as they considered decent. Aristotle certainly did his fair share of naked cogitation – after all, he invented formal logic and laid down the rules of argument as we know them today. But his real contribution was surely to put forward the then heretical view that if you want to know about the world, you must dissect and scrutinise it, not just think about it. So great was this break with Greek cultural norms that Aristotle felt obliged to devote several chapters of one of his major books on biology, The Parts of Animals, to justifying his empirical approach.
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But it paid off. Aristotle’s biology has stood the test of time in a way that his physics (which very conspicuously lacked an empirical dimension) has not. His major biological works (The Parts of Animals, The Natural History of Animals and The Reproduction of Animals) read almost like modern textbooks.
You might argue that this is simply because, unlike say physics, biology itself has not progressed much since Aristotle’s day. But that claim would be difficult to justify, if only because Aristotle’s biology fell into obscurity within a few generations of his death. (Indeed, all of Aristotle’s writings were lost: what we now have, we have only because a set of manuscripts was rediscovered by chance in a cellar in 80 BC, some 250 years after his death.) His reputation among the medieval scholars rested entirely on his achievements in logic and metaphysics. In stark contrast, they clearly considered his biology to be second-rate, for they frequently corrected his writings to save him from what they obviously considered to be embarrassing mistakes.
SAVING FACE
One example of this comes in Aristotle’s discussion of the honeybee. After presenting a lengthy summary of the bees’ biology, full of detailed observations of what bees actually do when they collect nectar from flowers and return to place it in the cells of the honeycomb to make honey, we suddenly find an apparently throwaway sentence asserting that, of course, we know this is not true because honey really comes from the air not from flowers. No evidence, no hypothesis testing, just a simple statement of ‘how it really is’. This has to be the work of a later commentator who, surprised to find the great master apparently making a claim that did not conform with the medieval view of things, added a correction to save the master’s face. His biology had to be rediscovered by later generations.
Time after time, Aristotle gets it right. He recognised the distinction between homologous and analogous parts – that some features of unrelated animal species are similar because they derive from the same common ancestor (like feathers and scales), whereas others represent convergent evolution from unrelated ancestors (like the wings of birds and insects). He realised from his detailed studies of anatomy that dolphins are mammals and not fishes (something that was not appreciated by some of the great founding fathers of modern taxonomy like the Swiss naturalist Charles Bonnet even as late as the end of the 18th century). He discovered that some sharks, certain dogfish for example, give birth to live young. This was not formally known until it was described by Steno in the 1650s.
He realised for the first time that the seed of a plant is equivalent to the embryo in animals; that the mammalian fetus is fed directly through the umbilicus (not by sucking on the villi that line the uterine wall as everyone had previously supposed); that some reef fish only occur in the female form (they are all genetically female, with the dominant female transmuting into a male); that the egg-white in a bird’s egg is not the equivalent of the mammal’s milk (the yolk is the nourishment for the growing embryo before it hatches); and that the sex of the embryo is determined at some very early stage in its development. He correctly described the biology of the honeybee, recognising that there is only ever one queen per hive (though he persistently calls her the ‘leader’ or ‘king’), that the worker bees are female and the drones are male, that there is always a small stock of new queens (‘leaders’) being hatched in a separate part of the hive; and that the bees collect pollen and nectar from flowers which they ‘vomit’ into the cells of the honeycomb. The biology of the honeybee was not correctly described again until the 1740s.
As a purely descriptive anatomist, Aristotle was second to none. He correctly described the Eustachian tube that links the middle ear with the throat: it was not to be described again accurately until the Italian Bartolomeo Eustachio did so in 1550. His account of the embryology of the chick developing in the egg was not bettered until the work of the great 17th century anatomist William Harvey. He was the first to describe the ana-tomy of the hyena correctly, recognising the distinction between males and females – the hyena had been thought to be a hermaphrodite, a belief that persisted even as late as the early part of this century in certain circles. He correctly described the way in which grasshoppers make their characteristic sounds by rubbing their legs against their wings, though he got it wrong in the case of both bees and cicadas. He realised that, in the octopus family, one arm is specialised for use as a copulatory organ for sperm transfer to the female. He discussed at great length the difference between epigenesis – the idea that an embryo develops gradually from a single undifferentiated egg cell – and preformation – the long since discredited theory that an egg (or sperm) contains a fully formed miniature individual – in the embryological development of organisms (anticipating a major debate in 19th century biology). He also anticipated the theory of cell-streams – the morphogenetic movement of cells along particular pathways that occurs when the germ layers are taking up their final positions in the body – a theory that was to become one of the cornerstones of modern embryology.
Although Aristotle did not have a theory of evolution (he thought species were more or less fixed for all time), he nonetheless understood the nature of adaptation (that organs are generally well adapted to the purpose they serve in the life of the animal). ‘Nature,’ he observes, ‘makes the organs to suit the work they have to do, not the work to suit the organ.’ Moreover, it is clear that he had recognised many of the principles that lie at the heart of modern evolutionary biology. He noticed, for example, that there is an inverse relationship between litter size and both the birth weight of individual infants and the amount of care given to each by the parents. Species tend to go for one of two extremes: many small babies with limited parental care (as in dogs) or one large offspring at a time on whom all the attention is lavished (as in humans and other higher primates).
He noticed that larger animals need larger ranging areas and that the body weight of animals of a given species depends on the quality of the habitat it lives in (both general principles of modern ecology). He identified a number of principles of reproduction that have only been reconfirmed within the last few decades in evolutionary biology: that there is a last-in/first-out principle in fertilisation among birds (that the sperm of the last male to mate is invariably the one that fertilises the egg), that there is an inverse relation between the effort devoted to reproduction and longevity (individuals who expend a lot of energy on reproduction tend to die prematurely); that large animals are less fecund than small ones; that males generally compete for access to females with whom to mate (rather than vice versa); and that female mammals eat more when they are pregnant.
And his marine biology was not bettered until marine biology became a discipline in its own right after the Second World War. He correctly noted, for example, that cartilaginous fish are linked together during mating. Marine biologists have commented that his knowledge could only have come from a close examination of fishing catches over several years or from direct observation.
No one gets it right all the time, of course. Inevitably, even Aristotle made mistakes, some of them astonishingly crass when seen with the benefit of hindsight. He realised that the male and female each make a separate contribution to conception, and that the male’s contribution comes in the form of sperm. But he thought that the female contribution took the form of menstrual blood. Among other claims that strike us as bizarre today are the suggestions that small insects like fleas and bugs are created out of mud more or less spontaneously, that eels don’t breed at all; that the larvae are the eggs of insects (in fact, they are the stage after the egg); that nerves are full of blood; that mice are so prolific that even the embryo is already pregnant; that the testes play a rather minor role in reproduction; and that menstruation occurs because of a periodic build-up of blood in the small veins far from the centre where blood is produced.
Some of these errors are, perhaps, understandable. After all, the European eel does not breed in Europe: it breeds in the Sargasso Sea in the mid-Atlantic and this was not discovered until the great age of exploration when Columbus came across it by chance during his first voyage to the Americas in 1492. After hatching in this mid-ocean tangle of seaweed, the leaf-like larvae drift eastward on the ocean currents to arrive as young elvers off the coast of Europe. And we can understand Aristotle’s mistakes about microscopic details like the development of fleas and bugs: after all, as late as the 18th century, it was still widely believed that swifts spent the winter buried in the mud at the bottom of village ponds.
In fact, if you look carefully at the things that Aristotle got right and those that he got wrong, they divide out rather neatly into things he could see or dissect with his own hands and things that he could not see either because they occurred in places he could not get to or because they require a microscope to see their details.
And, to give Aristotle his due, he does repeatedly caution his readers against assuming that he has got it right. ‘The facts have not yet been sufficiently ascertained,’ he warns in case after case. ‘If at any time in the future they are ascertained, then credence must be given to the direct evidence of the senses rather than to theories.’ Here is the master scientist at work. Although he was not the first empiricist among the ancient Greek philosophers – he himself repeatedly acknowledges the influence of predecessors like Empedocles and Democritus, albeit usually while correcting their mistakes – he was surely the greatest in both the scope of his interests and the meticulousness of his observations. Nothing was so trivial that it did not excite his interest. Modern science surely owes this canny old Greek’s ‘look and learn’ philosophy much more than it suspects.
Robin Dunbar is Professor of Biological Anthropology at University College London.
