or even a clearer exposition of, what Darwin was supposed to have meant by his term “natural selection”, Spencer misunderstood Darwin’s scientifically grounded theory, and he misapplied it as an endorsement of his sociological philosophy. The scientific historians, and philosophers, who have examined Spencer’s ideas have concluded that he saw evolution as a purposeful progression of the physical world, including all biological organisms, the human mind, and human culture and society. Unfortunately it was Spencer’s sociological concept of survival of the fittest, as opposed to Darwin’s scientific concept of natural selection, that led to the inaptly named Social Darwinism of the early nineteenth century, with all of its unfortunate ramifications.
There was never any true scientific foundation to Spencer’s ideas, but since they conveniently fitted with some of the prevailing prejudices of class, and the ethnic and racial bias of the late nineteenth century, extending into the first half of the twentieth century, they became deeply ingrained and influenced political and social belief. It is tragic that Spencer’s ideas still influence a lot of non-scientists today, so that one frequently hears the expression “survival of the fittest” raised in defence or excuse of some prejudicial action. So ingrained did Spencer’s ideas become that, during his lifetime, Darwin himself was put under a lot of pressure, by Spencer and others, to change his basic premise, but, although he briefly flirted with Spencer’s idea, he quickly recovered his senses and returned to his original concept.
Why am I making such a fuss of this when it might be argued that a similar concept of “fitness” is central to Darwinian theory even today? Of course fitness is a core concept to evolutionary biology, but this Darwinian expression is far from the judgemental notion proposed by Spencer. What then did Darwin really imply with his theory of evolution by means of natural selection, and how does the Darwinian concept of “fitness” differ from Spencer’s notion of “the survival of the fittest”?
Admirers of David Attenborough’s Blue Planet series will have observed how, in the warmth of summer, the female Atlantic lobster, a species that can grow up to 20 kilograms in weight, decides that the time has come to lay her eggs. She has already mated – often this happens as soon as she has moulted – but for seven months she has skulked from view in the freezing, deeper waters of the ocean, safe from predators and winter storms and patient in her determination to choose the most opportune moment for her offspring. But now her mind is made up, she is obliged to trudge her month-long marathon to the sandbanks of the warmer, surface waters, where, on her arrival, she must first do battle, claw for claw, with other lobsters to take control of her favoured sheltered pit. Here at last, some eight months after first fertilisation, she deposits her 20,000 or so eggs, which tumble into the pit from grape-like clusters beneath her abdomen, and from which her young emerge within minutes to take advantage of the warmth and limited shelter afforded by their mother’s endurance, discrimination and fortitude in battle. In the case of other marine invertebrate animals, such as sea urchins, and certain species of fish, a single spawning may give rise to millions of eggs. This behaviour, and the very production of vast numbers of potential offspring, is closely linked to what biologists actually mean when they talk about fitness in its true evolutionary meaning.
Fitness, from the Darwinian perspective, is a measure of how successful an individual is in his or her ability to reproduce and thus to contribute to the broad genetic pool of the species. It is a very simple, non-moralistic and non-judge-mental concept, the real emphasis of which is on reproduction. But, as we see with the lobster, this is more complex than merely laying eggs, or, in the case of human beings, bearing young in a womb. The individual has first to survive in the competitive theatre of life and then to compete with others of the same species for reproduction, and further to make possible, even in such limited life histories as that of the lobster, the survival of as many offspring as possible. In fact evolutionary biologists will usually measure comparative fitness of an individual within a species and what they look for is the proportional contribution of an individual’s genes to the species gene pool in a single generation.
Humans do not give birth to millions of eggs at a very early stage of embryological development, but rather to highly developed infants, which demands that they be nurtured for a very long period of time in the womb. For this purpose evolution has designed the human uterus as a single chamber, roughly the shape of an inverted pear, which is optimally designed for bearing a single foetus. The highest recorded number of living offspring born to a human mother in a single pregnancy is the eight babies born to an American mother in January 2009, all of whom lived. They were not conceived in the normal way but through assisted fertility treatment, and it is unlikely that all would have lived without the assistance of modern obstetric care. Indeed, obstetricians rightfully regard any increase above the normal single offspring as carrying an increased risk to both mother and offspring, even for twins.
Fitness, in human terms, is clearly more complex than we see in lobsters, but nevertheless the same basic non-Spencerian considerations apply, in terms of relative fitness.
The modern Darwinian concept of natural selection is brutally simple and depends on a system of probability, amenable to calculus. Where an individual of any species acquires some slight advantage in terms of survival over its fellows, it is more likely to survive long enough to have offspring, and if the advantage is hereditary, the offspring in turn will enjoy the same advantage over their own generation, so the advantage in time becomes part of the evolving species. From the fitness point of view, the hereditary advantage gives the individual, and its offspring at every subsequent stage of reproduction, the chance of making a bigger contribution to the species gene pool than the average member of the species. It’s really that simple. We can see, from the Darwinian standpoint, that relative fitness is a way of measuring advantage from a natural selection point of view. In time, particularly if the affected group within a species is isolated, geographically or otherwise, from the remainder of the species, an accumulation of such hereditary changes – or a rapidly developing major change – will so alter the affected group that they are no longer capable, or likely, to reproduce with members of the original species. This is the perfectly reasonable Darwinian explanation of how new species arise in a linear-with-branching pattern from ancestral species.
The creation of new species from old is termed “speciation”. Spencer, who was influenced by the French evolutionary biologist, Lamarck, believed that evolution was driving all of life, and most particularly the human species, towards a higher, utopian, destiny. But it is clear that Darwin’s theory of evolution by means of natural selection embraces no such ideal. On the contrary, selection works through the biological necessities of survival and comparative success in reproduction, which have nothing to do with morality, and have no in-built drive towards a philosophic, or religious, ideal of individual or societal perfection.
The concept of natural selection, as proposed by Darwin, was both logical and amenable to experimental confirmation, so that, in spite of considerable opposition from both Church and rivals within his own field, it appealed to the majority of scientists, and eventually to the educated society of his day. However, it embodied a weakness of which Darwin himself was well aware. For selection to work, it demanded a source, or sources, of hereditary change, which would give rise to the key advantages in survival, and thus relative fitness, of one individual, or group, over the others of its own species. Today we know that this implies some sort of genetic, or genomic, innovation, but Darwin was hampered by the ignorance of the mechanisms of heredity in his day. The very concept of genetics was unknown and the enlightenment of DNA would be unavailable until almost a century after publication of The Origin of Species. What Darwin achieved, given the science of his day, was, without exaggeration, world-changing. We cannot criticise him if he was obliged to fall back on now-outmoded concepts of parental mixing, or blending, as if the quaint notion of pedigree could somehow supply what we now realise to be the vast genetic and genomic change necessary to give rise to biodiversity. It was an inherent weakness in his theory that was unlikely to go away.
Thus it was not altogether surprising that, at Oxford, in 1894, during his presidential address to the British Association for the Advancement of Science, the Marquis of Salisbury
