It requires an effort of the imagination to recall just how recent a phenomenon complex forms of life on earth are. Picture a world in which the earth consisted of barren windswept rocks, in which the most complex forms of life were mats of algae and pond scum. This was the situation for the great majority of the earth’s history. For thousands of millions of years the development of life was virtually static. Then suddenly, this stagnant world erupted in one of the most dramatic explosions in the history of life. The fossil record now reveals an extraordinary proliferation of different forms of life. The emergence of animals with shells and skeletons preserves this progress in tablets of stone. The explosion of new forms of life in the oceans was paralleled by the mass extinction of the older stromatolites, which had been the dominant life form in the Proterozoic period. The appearance of a vast multitude of many-celled creatures transformed the face of the earth for all time. As Frank HT Rhodes wrote:

Perhaps the most remarkable (and also the most perplexing) thing about the fossil record is its beginning. Fossils first appear in appreciable numbers in rocks of the Lower Cambrian age, deposited about 600 million years ago. Rocks of older (Pre-Cambrian) age are almost completely unfossiliferous, although a few traces of ancient organisms have been recorded from them. The difference between the two groups of rocks is every bit as great as this suggests: a palaeontologist may search promising-looking Pre-Cambrian strata for a lifetime and find nothing (and many have done just this); but once he rises up into the Cambrian, in come the fossils – a great variety of forms, well-preserved, worldwide in extent, and relatively common. This is the first feature of the oldest common fossils, and it comes as a shock to the evolutionist. For instead of appearing gradually, with demonstrably orderly development and sequence – they come in with what amounts to a geological bang.[20]

In spite of his genius, Darwin was unable to come to terms with the Cambrian explosion. Clinging to his gradualist conception of evolution, he assumed that this sudden leap was only apparent, and due to the incompleteness of the fossil record. In recent years, new and startling discoveries in palaeontology have led to a major revision in the interpretation of evolution. The old idea of evolution as an uninterrupted process of gradual change has been challenged in particular by Stephen Jay Gould, whose investigations into the fossil record of the Burgess Shale (an important fossil location in British Columbia) have transformed palaeontology.

Life developed, not in a straight line of uninterrupted evolutionary progress, but through a process aptly described by Stephen Jay Gould as punctuated equilibria in which long periods of apparent stability are interrupted by periods of sudden and cataclysmic change characterised by mass extinctions of species. For 500 million years the borderlines of geological periods are marked by such sudden upheavals in which the disappearance of some species clears the way for the proliferation of others. This is the biological equivalent of the geological processes of mountain formation and continental drift. It has nothing in common with the vulgar caricature of evolution understood as a simple process of gradual change and adaptation.

According to the classical theory of Darwin the emergence of the first complex multicellular forms of life must have been preceded by a long period of slow progressive change, which culminated in the “Cambrian explosion” 500 million years ago. However, the most recent discoveries show that this is not the case. The investigations of Gould and others show that for two-thirds of the history of life on earth – nearly 2.5 billion years – life remained confined to the lowest recorded level of complexity, prokaryotic cells, and nothing else.

“Another 700 million years of the larger and much more intricate eukaryotic cells, but no aggregation to multicellular animal life. Then, in the 100-million year wink of a geological eye, three outstandingly different faunas – from Ediacara to Tommotian, to Burgess. Since then, more than 500 million years of wonderful stories, triumphs, and tragedies, but not a single new phylum, or basic anatomical design, added to the Burgess complement.”

In other words, the emergence of complex multicellular organisms, the basis of all life as we know it today, did not arise out of a slow, gradual “evolutionary” accumulation of adaptive changes, but in a sudden, qualitative leap. This was a veritable biological revolution, in which, “in a geological moment near the beginning of the Cambrian, nearly all modern phyla made their first appearance, along with an even greater array, of anatomical experiments that did not survive very long thereafter.” During the Cambrian period, nine phyla (the basic unit of differentiation within the animal kingdom) of marine invertebrates appeared for the first time, including protozoa, coelenterata (jellyfish, sea-anemones), sponges, molluscs and trilobites. It took about 120 million years for the complete range of invertebrate phyla to evolve. On the other hand, we had the rapid demise of the stromatolites, which had been the dominant life form for two billion years.

“Modern multicellular animals make their first uncontested appearance in the fossil record some 570 million years ago – and with a bang, not a protracted crescendo. This ‘Cambrian explosion’ marks the advent (at least into direct evidence) of virtually all major groups of modern animals – and all within the minuscule span, geologically speaking, of a few million years.”(Gould)[21]

For SJ Gould, “We find no story of stately progress, but a world punctuated with periods of mass extinction and rapid origination among long stretches of relative tranquillity.”[22] And again:

The history of life is not a continuum of development, but a record punctuated by brief, sometimes geologically instantaneous, episodes of mass extinction and subsequent diversification. The geological time scale maps this history, for fossils provide our chief criterion in fixing the temporal order of rocks. The divisions of the time scale are set at these major punctuations because extinctions and rapid diversifications leave such clear signatures in the fossil record.[23]

  1. Rhodes, F. The Evolution of Life, pp. 77-8.

  2. Gould, S. Wonderful Life, pp. 60, 64 and 23-4.

  3. Gould, S. Ever Since Darwin, p. 14.

  4. Gould, S. Wonderful Life, p. 54.