The first part of The Island of the Colorblind was an interesting and sometimes inspiring account of people overcoming a rare visual defect.

The second part was overtly about Lytico-bodig, which is much more debilitating and degenerative, and therefore depressing. The good news is that the disease is dying out, but Dr. Sacks seemed a bit chagrined to think that the disease would disappear before its cause could be definitively identified.

Part 2 was also a grim reminder of the consequences of conquest. Melville described the idyllic life of a Polynesian; Jack London visited 65 years later and found "some dozen wretched creatures, afflicted by leprosy, elephantiasis, and tuberculosis."

But the second section was secretly a hymn in praise of the cycad, an ancient survivor, which inspired a visit to the Botanic Garden on Sunday.

I mentioned earlier that the end notes (expanded in a later edition) in a Sacks book are wonderful. Here are two.

68 It is sometimes said (the term goes back to Charcot) that patients with Parkinson’s disease have a ‘reptilian’ stare. This is not just a picturesque (or pejorative) metaphor; normal access to the motor functions, which gives mammals their delicate motor flexibility, is impaired in parkinsonism; this leads to alternations of extreme immobility with sudden, almost explosive motion, which are reminiscent of some reptiles.

Parkinson himself was a paleontologist, as well as a physician, and his 1804 book, Organic Remains of a Former World, is one of the great pioneer texts of paleontology. One wonders whether he may have partly regarded parkinsonism as an atavism, a reversion, the uncovering, through disease, of an ancestral, ‘antediluvian’ mode of function dating from the ancient past.

Whether or not this is so of parkinsonism is arguable, but one can certainly see reversion to, or disclosure of, a variety of primitive behaviors in post-encephalitic syndromes on occasion, and in a rare condition, branchial myoclonus, arising from lesions in the brain stem. Here there occur rhythmic movements of the palate, middle-ear muscles, and certain muscles in the neck – an odd and unintelligible pattern, until one realizes that these are the only vestiges of the gill arches, the branchial musculature, in man. Branchial myoclonus is, in effect, a gill movement in man, a revelation of the fact that we still carry our fishy ancestors, our evolutionary precursors, within us.

75 The Copernican revolution in the sixteenth and seventeenth centuries, with its revelation of the immensity of space, dealt a profound blow to man’s sense of being at the center of the universe; this was voiced by no one more poignantly than Pascal: ‘The whole visible world is but an imperceptible speck,’ he lamented; man was now ‘lost in this remote corner of Nature,’ closed into ‘the tiny cell where he lodges.’ And Kepler spoke of a ‘hidden and secret horror,’ a sense of being ‘lost’ in the infinity of space.

The eighteenth century, with its close attention to rocks and fossils and geologic processes, was to radically alter man’s sense of time as well (as Rossi, Gould, and McPhee, in particular, have emphasized). Evolutionary time, geologic time, deep time, was not a concept which came naturally or easily to the human mind, and once conceived, aroused fear and resistance.

There was great comfort in the feeling that the earth was made for man and its history coeval with his, that the past was to be measured on a human scale, no more than a few score of generations back to the first man, Adam. But now the biblical chronology of the earth was vastly extended, into a period of eons. Thus while Archbishop Ussher had calculated that the world was created in 4004 B.C., when Buffon introduced his secular view of nature – with man appearing only in the latest of seven epochs – he suggested an unprecedented age of 75,000 years for the earth. Privately, he increased this time scale by forty – the original figure in his manuscripts was three million years – and he did this (as Rossi notes) because he felt that the larger figure would be incomprehensible to his contemporaries, would give them too fearful a sense of the ‘dark abyss’ of time. Less than fifty years later, Playfair was to write of how, gazing at an ancient geologic unconformity, ‘the mind seemed to grow giddy by looking so far into the abyss of time.’

When Kant, in 1755, published his Theory of the Heavens, his vision of evolving and emerging nebulae, he envisaged that ‘millions of years and centuries’ had been required to arrive at the present state, and saw creation as being eternal and immanent. With this, in Buffon’s words, ‘the hand of God’ was eliminated from cosmology, and the age of the universe enormously extended. ‘Men in Hooke’s time had a past of six thousand years,’ as Rossi writes, but ‘those of Kant’s times were conscious of a past of millions of years.’

Yet Kant’s millions were still very theoretical, not yet firmly grounded in geology, in any concrete knowledge of the earth. The sense of a vast geologic time filled with terrestrial events, was not to come until the next century, when Lyell, in his Principles of Geology, was able to bring into one vision both the immensity and the slowness of geologic change, forcing into consciousness a sense of older and older strata stretching back hundreds of millions of years.

Lyell’s first volume was published in 1830, and Darwin took it with him on the Beagle. Lyell’s vision of deep time was a prerequisite for Darwin’s vision too, for the almost glacially slow processes of evolution from the animals of the Cambrian to the present day required, Darwin estimated, at least 300 million years.

Stephen Jay Gould, writing about our concepts of time in Time’s Arrow, Time’s Cycle, starts by quoting Freud’s famous statement about mankind having had to endure from science ‘two great outrages upon its naive self-love’ – the Copernican and Darwinian revolutions. To these, Freud added (‘in one of history’s least modest pronouncements,’ as Gould puts it) his own revolution, the Freudian one. But he omits from his list, Gould observes, one of the greatest steps, the discovery of deep time, the needed link between the Copernican and the Darwinian revolutions. Gould speaks of our difficulty even now in ‘biting the fourth Freudian bullet,’ having any real, organic sense (beneath the conceptual or metaphoric one) of the reality of deep time. And yet this revolution, he feels, may have been the deepest of them all.

It is deep time that makes possible the blind movement of evolution, the massing and honing of minute effects over eons. It is deep time that opens a new view of nature, which if it lacks the Divine fiat, the miraculous and providential, is no less sublime in its own way. ‘There is grandeur in this view of life,’ wrote Darwin, in the famous final sentence of the Origin, ‘that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.’