Abstract
Charles Robert Darwin was born 200 years ago on 12 February 1809 in Shrewsbury, Shropshire, England. His landmark work The origin of species was published in November 1859, hence it seems fitting that our November edition is dedicated to his massive scientific achievement. The son of a physician, Charles commenced studying medicine at the University of Edinburgh but seems to have had little enthusiasm for it and little more for theology, his father' second choice. Both at Edinburgh and Cambridge his childhood interest in natural history seems to have captivated him, with his establishing a number of valuable contacts including Professor of Botany, the Reverend John Henslow. Henslow it was who later put Darwin' name forward as a suitable gentleman companion and naturalist to accompany Captain Robert Fitzroy on HMS Beagle's famous voyage to chart the coastline of South America.
While on this 5 year voyage that involved a return to England via New Zealand and Australia, Darwin amassed a vast number of specimens and data that kept him busy for the rest of his life [1,2]. His limited time in Australia and New Zealand was not the highlight of his voyage, but the strangeness of Australia' animals stimulated his reflections on the origin of species.
The origin of species was revolutionary in its day. Darwin was not the first to propose an evolutionary theory of life but he was the first to develop a comprehensive theory based on natural selection. Doing so won him both friends and enemies, the latter including Richard Owen, a leader of the scientific establishment. Another, the Bishop of Oxford, Samuel Wilberforce, is famously known to have verbally and publicly duelled with Thomas Huxley, Darwin' champion, interrupting Huxley' speech at an Oxford debate to ask him whether it was on his grandmother' or grandfather' side that he was related to an ape. Huxley is said to have replied that he would rather “have a miserable ape for a grandfather than a man possessed of great means of influence and yet who employs… that influence for the mere purpose of introducing ridicule into a grave scientific discussion.” [3].
The origin of species was published after more than 20 years deliberation. What is striking about reading it today is Darwin' meticulous attention to detail and how tame its message now seems. This suggests that his ideas have been thoroughly integrated into modern scientific and even lay thought. Darwin' contemporary and close friend, Captain Fitzroy, sadly thought otherwise. Despite a continued successful naval career, Fitzroy, an intensely but inflexibly religious man of great fortitude, competence and generosity became severely depressed about his own involvement in what he viewed as sacrilegious results from his friend Darwin' theories from their 5 years together on the Beagle. He never came to terms with this and 5 years after the publication of The origin of species he fatally cut his throat [4]. The origin of species was followed in 1871 by The descent of man, in which Darwin finally took the plunge and included Homo sapiens in deliberations and developed his ideas on sexual selection.
Today 150 years after the publication of The origin of species virtually all of biology uses evolution as its foundation. Psychiatry still manifests a reticence, however, about evolution that would have done Bishop Wilberforce proud. It remains more the exception than the rule that relevant psychiatric papers give proper consideration to the wealth of evolutionary data and knowledge that are now available. Studies on the genetics of mental disorders seldom interpret the findings within an evolutionary framework.
The desirable marriage of genetics with evolutionary theory was emphasized back in 1973 by evolutionary geneticist Theodosius Dobzhansky in his provocative paper, “Nothing in biology makes sense except in the light of evolution” [5]. Jaak Panksepp in his exceptional text published in 1998, Affective neuroscience: the foundations of human and animal emotions, more recently called for the coming together of evolution with genetics in the study of neuroscience [6].
Without the coming together of evolution and genetics in the study of mental disorders, it is unlikely that the current diagnostic framework, captured by DSM-IV and ICD-10, will be validated. Most of the mental disorders reflect distress, dysfunction, dyscontrol, disadvantage, disability, inflexibility, irrationality, syndromal pattern, and statistical deviation. There have now been enough genomewide association studies of the major mental disorders to know that there are not going to be simple associations between any one gene and any of the major mental disorders. Yet genes are the building blocks of contemporary neuroscience, so we need to consider the phenotypes we currently call disorders. One possibility is that genes are relevant to mental disorders because they influence our tendency to approach, tendency to withdraw, reactions to stressors, need for others, our cognitive styles and capacity, and our responses to rewards and punishments. Another possibility is that there are multiple rare genes with large effects. One gene, however, may be related to more than one disorder, and one disorder may have multiple genes that confer risk.
It is also possible that genes contribute to high frequencies of mental disorders because their disadvantages may have in some ways been offset by characteristics that are or were advantageous in ancestral evolutionary environments. Attention-deficit–hyperactivity disorder is often a disadvantage in our sedentary modern cultures but may have been an asset in ancestral environments. Simply put, some disorders may have been or still be adaptive, increasing the likelihood that the associated genes will be transmitted to future generations. Evolutionary psychiatry, however, is by no means limited to all things adaptive, and to assume adaptiveness without evidence is scientifically unacceptable. Darwin required a massive amount of observations before he would accept the theories of adaptations to which they pointed.
Another very common aspect of this paradox is that a small dose of a characteristic may be adaptive while a large dose is maladaptive. In male organisms both height in humans and the size of ornate tail feathers in peacocks carry advantages in terms of sexual selection. They advertise male fitness, both in terms of health and potential competitive strength. The reason these traits have not escalated to more absurd proportions, however, is that to do so would carry liabilities with respect to natural selection. Trade-offs may be involved. For instance, the large human brain carries many benefits, but at the price of elevated perinatal and maternal mortality [7].
There are other issues in the adaptiveness paradox [8]. If a characteristic is maladaptive in the current environment, time will be required for its elimination. Elimination will be even more extended if the characteristics cause only modest reductions in fitness. Further, if the disorders emerge only after peak reproductive periods, for example. Alzheimer' and Huntington' diseases, the maladaptive traits will be more likely to persist. Also some pathology may be clinically unfounded: fevers may actually shorten some infections provided the clinician' enthusiasm for intervention does not interfere with this [9].
The increasing recognition of the importance of epigenetic research is another reason for the coming together of neuroscience with evolutionary theory. The increasing use of the term ‘epigenetics’ almost suggests that it is new, yet it has been integral to evolutionary psychiatry, even though evolutionary psychiatry at times has been guilty of neglecting to link the macro perspective of evolutionary theory with the micro perspective of genes. Genes provide potential that generally has to be activated by the environment: chemical, social or other. Gardner coined the term ‘sociophysiology’ in recognition of the major contribution of social processes to health or adverse psychophysiology [10]. External events activate physiological phenomena. Social ranking and ingroup–outgroup dynamics are two examples of powerful social influences on health that have been under-utilized by traditional psychiatry. Far from being merely a cultural source of inequity, social ranking pervades the human and animal world. The politics of ingroup–outgroup phenomena was exploited by former president Bush in his call to the world that ‘You are either with us or against us’. In everyday life away from politics group affiliation fosters health while outgroup status does the reverse.
While biopsychosocial psychiatry is widely espoused, the reality is that the three domains of the biological, psychological and social are too often conceived of as unrelated. Approaches such as those captured by the terms ‘sociophysiological’ or ‘psychobiological’ are more likely to provide a framework for true integration. Let us illustrate: a young male primate has unsuccessfully challenged an alpha male. In addition to licking its physical wounds it retreats to the periphery of the group and for some months its behaviour appears socially withdrawn, uncharacteristically timid, weary, lacking in motivation, almost as if it were ill. Depression in this instance serves the survival function of preventing a further challenge that might incur fatal, or other serious, retribution. Where is the separateness of biology, psychology and sociology? Evolutionary psychiatry may provide the ultimate integration of the related biological, psychological and social domains.
Research increasingly is suggesting that many mental disorders, particularly depression and anxiety states, exist in animals. Animal behaviourists have routinely acknowledged the importance of natural selection and adaptations with respect to such disorders. Psychiatrists have tended to emphasize the obvious human differences from animals. Animal psychiatry is one step further removed. Yet the detection of true commonalities in human and animal psychopathology would go a long way towards clarifying true pathophysiological or diagnostic entities, their causation, their phenomena and moderating variables.
In this issue, which recognizes the contribution of Darwin to our intellectual heritage, we challenge psychiatry to take up the task of integrating our clinical practice into an evolutionary framework, for as Dobzhansky might have said, nothing makes sense in psychiatry except in the light of evolution. This is not a simple challenge, because our understanding of the evolution of human behaviour and consciousness is far from complete. Much may be gained by exploring neglected domains, for many new ideas and lines may be revealed.