DAVID HULL AT SEVENTY

       This last June (2005) David Hull and I took a trip to Scotland to visit Glen Roy. This is a small valley, in the shadow of Ben Nevis, off the Great Glen of Scotland that splits the highlands in two. In fact, we stood at the mouth of the glen on June 15, David’s seventieth birthday. It was a typical Scottish summer’s day – cold and wet. Yet for both of us, two people who have written extensively through their academic careers on Charles Darwin, it was a terrific thrill. Why was this?

      In his Autobiography, Darwin rather presents himself as lazy dolt, especially when he was at school. In fact, this is rather misleading. In those days, school (what Americans would call “high school” and what the English perversely call “public school,” meaning private school) had an uninterrupted diet of classics, first Greek and then Latin, and then Greek again. Anyone interested in science was considered a weirdo and a bit thick. Darwin was interested in science – he and his older brother experimented with chemistry – and this interest continued while he was at university, first somewhat unsuccessfully training to be a doctor at Edinburgh University and then somewhat more successfully training to be an Anglican clergyman at Cambridge University.

       By the time he graduated in 1831, he and others were starting to realize that, although he was not mathematically gifted, he had real talent both as an observer of nature and as a theoretician. Through a friend of a friend, Charles Darwin then set off for five years on HMS Beagle, spending most of the time going around and over South America but ultimately all the way around the world. Although he joined the ship as a kind of companion to the captain, rapidly he evolved into the ship’s naturalist and made major collections which were shipped back to England. By the time he returned, Darwin had established his status of one’s of the country’s really good, up-and-coming young scientists.

      Darwin of course was to make his mark as a biologist, the father of evolutionary theory. But his early work was as a geologist – he had a crash course before the Beagle voyage with Adam Sedgwick the professor of geology at Cambridge, and it was this science that really engaged him in the first ten years of his career as a scientist. Around the time that Darwin set off on his trip, British geologists were divided into two camps. On the one side, there were the so-called “catastrophists” like Sedgwick who thought that the earth was cooling and that it was being made ready for humans, and that every now and then it was interrupted by a major upheaval. On the other side, there were the “uniformitarians,” led by the Scottish-born geologist Charles Lyell, who argued that the processes of the present are enough to explain all of the events of the past, given enough time, and that the earth is in a kind of steady state, with no essential change from one era to another. The assumption that the processes are unchanging, known technically as “actualism,” is not the same as the assumption that the earth is in a steady state. One can be an actualist and think that the earth is directionally getting cooler. I presume that this is the position held today by most geologists.

      Lyell’s steady-state assumption was part and parcel of a religious commitment to a God who does not interfere with the creation. This is known as “deism,” as opposed to the belief in a God who does interfere, “theism.” Christians are theists. Traditionally, Unitarians – with whom Lyell worshipped – are deists. They think that Jesus was just a good bloke but not the son of God. Hence, the miracles associated with his name did not involve actual interference with the laws of nature. Darwin took with him the first volume of Lyell’s seminal Principles of Geology (the other two volumes were sent out as they appeared). He was seduced by the approach. It fitted nicely with the religious move he was then making from the theism of Christianity to a kind of deism, which latter persisted right through the writing of the Origin (all of those comments about the Creator were meant literally). Towards the end of his life, Darwin’s religion faded into a kind of agnosticism. (The Wedgwoods, the family of Darwin’s mother and his wife, were Unitarians.) At once, Darwin faced the major problem that confronted any uniformitarian. If the earth is in a steady state, then how do you account for the seeming changes – the fact that Paris once was much warmer, if one judges from the palm trees to be found in the fossil record?

      Lyell had proposed his “grand theory of climate.” He argued that the world is like a massive water bed – as one part gets depressed (for instance a river mouth by the weight of the silt accumulating from the erosion of mountains higher up), other parts will get elevated. This causes a redistribution of land and sea – note it is a redistribution brought by movement up and down rather than to and fro as supposed by plate tectonics – and with this distribution comes change in climate. It is fortuitous that today the poles are frozen and the equator is hot – it could have been the other way around. Thus we have an explanation of hot places now cold or conversely. There is some change, but always within limits and never final or unidirectional. (In case this all sounds somewhat ad hoc, we can point out that Lyell lived in Britain, much warmer than its latitude suggests because of the Gulf Stream.) Darwin did two notable pieces of geologizing and both should be understood within the Lyellian framework, most particularly within the Lyellian steady-state framework.

David and Michael at Down House

      First was his theory of coral reefs. One finds in the tropics that islands are frequently surrounded by circular reefs of coral. Sometimes the reefs are there with no islands. Lyell himself had supposed that extinct volcanoes just broke the surface of the water and coral grew on their rims. Darwin pointed out how unlikely it was that so many volcanoes would fortuitously just break the water’s surface. He suggested rather that coral (which can only live at the water’s surface) first accumulates around the edges of islands, and then these islands start to sink (presumably under the weight of the coral) and the coral keeps growing upwards to remain at the water’s surface. Sometimes the islands vanish entirely but the coral reef remains. Although hardly earth shattering (nice metaphor!), this is properly generally regarded as a very nice piece of science, and borings of coral reefs confirms that Darwin was right. The second geological exercise was less successful – Darwin himself acknowledged it to be his biggest mistake – but it too was part of the Lyellian steady-state picture. (Indeed, Lyell himself mentioned the phenomenon in the Principles and speculated along the lines that Darwin was to follow.) Glen Roy is, as I have said, a small valley up in the Scottish highlands. It is notable because around its sides are three parallel tracks or “roads” as they are known. What caused these roads? Some had thought that they might be ancient hunting paths, but by Darwin’s time general opinion was that they were the beaches of long-gone water in the valley. What was the nature of the water and where is it now? There were two hypotheses. One was that it was the sea, which has now retreated and the other was that it was a lake which has now vanished. Darwin opted for the sea hypothesis, arguing that the glen has risen along with the rest of northern Scotland, as a Lyellian might expect. The sea has now run out. One might however except to find sea shells on the roads, and in 1838 Darwin dashed up to Scotland to see for himself. He did not find any such shells, but in a move to be repeated in the Origin when faced with no fossil evidence before the Cambrian, he argued that one would not expect to find evidence!!! He argued that natural processes would have dissolved any such shells. And so this was the position taken in the paper Darwin published, the only one that he placed in the prestigious Transactions of the Royal Society, appearing in 1839. (The referee was Adam Sedgwick.)

      Although Sedgwick was the leading catastrophe theorist, relations between the two geological camps were very warm and friendly. This was not a division to cause personal ruptures, as was evolution. Although, as it happens, for all that Sedgwick was vehement against the Origin, he still stayed friendly with Darwin, referring to himself as a “son of a monkey.” Darwin was not stupid in arguing for the sea hypothesis. If there was a lake, where now is the barrier at the entrance to the valley? The answer, as was given in the early 1840s by the then-Swiss ichthyologist Louis Agassiz (later to move to Harvard and oppose the evolutionary thinking of Asa Gray), was that there was a lake and that it was dammed in by a glacier, which has since melted. Knowing all about these things from his home land, Agassiz was able immediately to point out that the rocks at the entrance to the glen have the striated marks of glaciation, as one would expect. Many years later, Darwin recognized that Agassiz was right and that he himself was wrong.

      Why did it take so long for the truth to be recognized? Was Darwin just being stubborn? In part, this is clearly true, but that it itself is no fault. Popper may be right about falsification (I myself think Popper is a lot more right than many of today’s philosophers of science allow), but there is no sin in holding on to a hypothesis until one is forced into the ground. Sometimes such an attitude pays big dividends. However, for Darwin (and Lyell) the problem was that Agassiz was using Glen Roy to support his theory that the world had been partly covered by ice – the Ice Age Theory, in fact. Again you might say, so what? We now agree that Agassiz was right. There were ice ages. The trouble was that Agassiz located this theory in a catastrophic view of history – bad news for the uniformitarians Lyell and Darwin – and linked this to God’s actions in the world – really bad news for the deists. (Amusingly, when the Calvinist Agassiz crossed the Atlantic, leaving his first wife behind to die alone, he then married a Boston Brahmin and adopted her religion, namely Unitarianism!) So you see, there is really quite a story to Glen Roy and that is why it was such a thrill and a privilege to stand in it on June 15, 2005, the seventieth birthday of my best friend and the man to whom in this world I owe more than to any other person, except my beautiful wife Lizzie. For those who want to dig more deeply into the Glen Roy affair, the definitive starting place is Rudwick, M J S. 1974. Darwin and Glen Roy: a 'great failure' in scientific method? Studies in the History and Philosophy of Science 5: 97-185.