/ 27 November 2009

A slow evolution of theory

This year marks the 200th anniversary of Charles Robert Darwin’s birth. And this week — Tuesday November 24 — marks the 150th anniversary of the publication of the first edition of his greatest work, The Origin of Species by Means of Natural Selection.

In this Darwinian year, literally hundreds of celebrations have taken place all over the world.

In South Africa alone there was a birthday party at the Wits Institute for Human Evolution on February 12, the date of Darwin’s birthday.

In Durban the Natural Science Museum was the venue for a Darwin Now exhibition, sponsored by the British Council, which I had the privilege of opening on September 9.

When the International Union of Biological Sciences held its first meeting in Africa — at the University of the Western Cape — the programme included a symposium on Darwin’s life and works on October 12.

Darwin was a gentle, neurotic Englishman who, after his abortive start with the study of medicine at Edinburgh — where he couldn’t stand anatomy — turned to theology at Cambridge. He was passionate about beetles and hunting and he tells us that he spent three happy and healthy years at Cambridge.

Then, at the age of 22, he set off on board HMS Beagle on the circumnavigation of the globe (1831 to 1836).

His specimen collecting, especially in the coastal regions and islands of South America, gave him the facts and thoughts that were to provide the warp and woof from which his theory of the origin of species by means of natural selection was to be woven.

Hear his own words: ‘The voyage of the Beagle has been by far the most important event in my life, and has determined my whole career — I have always felt that I owe to the voyage the first real training or education of my mind; I was led to attend closely to several branches of natural history, and thus my powers of observation were improved.”

But he cannot resist adding, ‘though they were always fairly developed —”

He continues: ‘The above various special studies were, however, of no importance compared with the habit of energetic industry and of concentrated attention to whatever I was engaged in, which I then acquired.

Everything about which I thought or read was made to bear directly on what I had seen or was likely to see; and this habit of mind was continued during the five years of the voyage. I feel sure that it was this training which has enabled me to do whatever I have done in science.”

The essence of Darwin’s vital contributions was twofold. He was not the first scholar who held that species had changed with time or evolved; even his grandfather, Erasmus Darwin, was a confirmed evolutionist — as is clear from a perusal of Zoonomia, the two volumes of which were published in 1794 and 1795.

It was, however, Charles Darwin’s lot to produce so voluminous and so systematic a body of evidence as to make the acceptance of evolution irresistible.

Second, it was not enough to produce the evidence that living things had evolved: what was needed was a hypothesis to explain how evolution could have occurred — and that was the concept of natural selection.

Again, he was not the first person to voice this idea: his grandfather, Erasmus, had also toyed with this notion, while his contemporary, Alfred Russel Wallace, alighted on the same idea while he was in the throes of intermittent fever, probably malaria, on the isle of Ternate in the Moluccas or the Spice Islands of today’s Indonesia.

As Frank Spencer put it, the solution of the species problem came to him (Wallace) in a serendipitous flash, whereas Darwin had first adumbrated the theory soon after the return of the Beagle.

Darwin’s patient, dogged, painstaking development and elaboration of natural selection over 20 years — even though he did not publish it during that time — was in sharp contrast with the feverish flash that carried Wallace to the same hypothesis.

It was not surprising that the principal authorship of natural selection is attributed to Charles Darwin, while Wallace himself, with customary generosity of spirit, proposed that this mechanism of evolution should be called Darwinism.

Scientists in South Africa are no less interested in the Darwinian anniversaries this year than are those elsewhere. An extra little zest of motivation flows from the visit of the Beagle to the Cape between May 31 and June 18 1836, in the last of the five years at sea.

Our colleagues in the Cape, justifiably proud of the Darwin link, have produced a delightful pamphlet, The Darwin Trail: Retrace Charles Darwin’s Visit to the Cape.

They point out that of the 13 ports where the Beagle called, on its homeward voyage from South America to England, the ship stayed longer at Simon’s Town Bay than anywhere else, except for the Galapagos Islands.

At Simon’s Town Darwin reported there was nothing worth seeing! Even on his journey to Cape Town on a gig, he reported that ‘the country is very desert; and with the exception of the pleasure which the sight of an entirely new vegetation never fails to communicate, there is very little of interest”.

However, he changed his tune over the next few weeks. During his visit Darwin was enthralled to have dinner with Sir John Herschel, whose Introduction to the Study of Natural Philosophy he had read at Cambridge, as he had Humboldt’s Personal Narrative.

He knew of Andrew Smith’s illustrations of the animal life of South Africa and was jubilant to receive a personal copy from him.

Darwin’s recognition of the geological significance of the Sea Point contact played a part in the evolution of his ideas on catastrophic changes in the history of the rocks and of life.

When HMS Beagle arrived back in England in 1836, it was to mark the onset of chronic, intermittent illness that persisted for the rest of his life, another 46 years.

Theories abound on the nature of Charles Darwin’s ailment. It seems he was almost certainly the victim of a family neurotic tendency, signs of which were evident among his forebears and descendants.

But was a double pathology operating in his case?

In 1959 Saul Adler published an amazing quotation in the form of a hitherto neglected passage in the Journal of Researches During the Voyage of HMS Beagle (CR Darwin, 1860). In 1835 the Beagle had dropped anchor in Valparaiso.

Darwin and a party of ships’ officers set out from Santiago to cross the Andes by way of the Portillo Pass. Travelling northwards on the pampas Darwin encountered the Benchuca, ‘the great black bug of the pampas”.

He described how he and the officers spent several nights in the huts of local people at Luxan village, south of Mendoza.

During the night he and the officers were ‘attacked” by this reduviid bug, which sucked their blood and changed from a flattened form to a full, rounded and swollen shape, almost like a grape.

At the time when Darwin was exposed to the bite of these assassin bugs, it was not known that this creature was the most important vector of a parasite, Trypanosoma cruzi, shown 75 years later to be the causative agent of Chagas’s Disease.

Not all bugs are infected with the trypanosome, but the province of Mendoza has a relatively high incidence of this disease. Thus Darwin was definitely exposed to the possibility of infection at least once, as Adler unearthed in l959.

I explored this account in my essay on the centenary of The Descent of Man (1871), which I presented as an Orenstein Lecture on September 30 1971.

At that time I stated that Darwin’s post-Beagle medical history was compatible with his having been a chronic sufferer from Chagas’s Disease, but I was forced to conclude — as Adler had done — that we shall never know for sure.

However, I added that ‘it is equally true that there is not sufficient evidence on which to exclude Chagas’s Disease from the differential diagnosis”.

It is amazing to realise that the major published works of Darwin, those monumental monographs — The Origin of Species, Variation Under Domestication, The Descent of Man and The Expression of the Emotions, including his (and Alfred Russel Wallace’s) theory of natural selection — were published when Darwin was aged 50 and older and were torn from a body and mind racked by illness and pain.

If we bear this in mind, we cannot help but doubly and trebly admire his accomplishments. It impels one to the general conclusion that the presence of disease, whether of mind or of body — or both, as in this case — is no absolute hindrance to great research achievements.

After decades when I and others strove to have the teaching of evolution introduced into South African schools, it is gratifying that this has now come to pass.

I am sure that the chronic invalid, Charles Darwin, would have cause to rejoice — and to record a double- dash, better day in his log-book of wellness and unwellness.

Professor Phillip V Tobias is honorary professorial research fellow in the school of anatomical sciences at the University of the Witwatersrand’s Medical School and is a member of the Institute for Human Evolution. This article is based in part on an address he delivered to the International Union of Biological Sciences, meeting for the first time in Africa, at the University of the Western Cape on October 12 and, in part, on his opening address to the Charles Darwin Exhibition in the William Cullen Library of Wits University on November 22. The latter address also opened the exhibition to mark the 75th anniversary of the opening of the William Cullen Library