Some 543 million years ago, the "Cambrian explosion" took place - the most decisive event in the history of life. Within a very few million years, the number of marine invertebrate phyla leapt from three to today's 38; the short, simple food chains of late Precambrian time were abruptly replaced by multitrophic and competitive ecosystems, and predators appeared for the first time. Marine animals with hard shells proliferated dramatically, fully organised and differentiated on their first appearance.
Whereas this phenomenon has been extensively researched, some mystery remains as to why it happened and at the time it did. Was it driven by physicochemical changes in the environment, for example warming of the oceans, flooding of continental shelves, increased availability of phosphorus following oceanic overturn, the build-up of free oxygen? And what of biological factors? Can traditional concepts fully explain life's big bang? Andrew Parker thinks not.
In his fascinating book, Parker, a biologist who has specialised in light and colour in living animals, develops a novel hypothesis, that of the Cambrian light switch. Put simply, it states that once the first real eyes originated, animals that possessed them would have had a phenomenal advantage over those that did not. In the author's words: "The most powerful sense of all had been launched on Earth. Suddenly, and for the first time, an animal could detect anything in its environment. And it could detect it with pinpoint accuracy." The possession of eyes would be an essential step in becoming a predator. Equally, there would be intense selection pressure on survival strategies among the hunted, and the origin of hard parts. The rapidity of the big bang is directly related to the origin of eyes.
Parker's book is pleasantly readable. The first chapters deal with the history of life and the Cambrian explosion. The middle section deals with light and colour in the animal kingdom, including life at night and in the deep sea, and the author's work on light flashes in marine ostracodes. Then he tackles the various kinds of eyes in the Cambrian, including those of trilobites.
He looks at the origin of eyes, including the classic work of Dan-Erik Nilsson and Suzanne Pelger, who calculated that a patch of light-sensitive cells could evolve into a camera eye within 364,000 generations, in less than 500,000 years. Then the full argument for the light-switch hypothesis is developed, linked to the multiplicity of marine animals in the Cambrian and today.
In the final chapter, the author speculates on why the first eyes originated when they did. Parker's theory is appealing and attractive. But I do have some criticisms. The author is too dismissive of the hypotheses based on geological evidence. And, having studied trilobites for 45 years, I would still hesitate to state that the earliest trilobites were predators; we lack the evidence; perhaps, if the book had been read in detail by a palaeontologist before publication, these minor irritations could have been avoided. However, I found it an enthralling read.
Controversial perhaps, but illuminating.
Euan Clarkson is emeritus professor of palaeontology, University of Edinburgh.
In the Blink of an Eye: The Cause of the Most Dramatic Event in the History of Life
Author - Andrew Parker
Publisher - Free Press
Pages - 316
Price - £18.99
ISBN - 0 7432 1980 5