New look at the living world

DEEP TIME - Cladistics, the Revolution in Evolution: Henry Gee; Fourth Estate Ltd., Salem Road, London W2 4BU. p. 20.

THE AUTHOR of this book is a Senior Editor at Nature. In Deep Time - a term coined by McPhee, a well-known writer in geology - the author has questioned many hypotheses on evolution generally held sacrosanct and introduces the reader to a new method called ``cladistics'' which is adopted by real scientists studying evolution. It is a new way of looking at the living world in terms of how they shared characteristics with one another without making unsustainable assumptions about ancestry and descent. Without cladistics, says the author, palaeontology is no more a science than the one that proclaimed that the Earth was 6000 years old and flat, claiming Divine sanction for this view.

The pioneering geologist, Charles Lyell, was among the first geologists to state that the Earth was much older than stated in the Bible. In doing so they discovered what, many years later, came to be termed as ``Deep Time'' by McPhee. Cladistics is concerned with the pattern produced by the evolutionary process but is not concerned with the process that created the pattern. It is hailed as the true, scientific heart of palaeontology. Unfortunately the media hype on evolution and a whole lot of mish-mash of related trivia bandied about in the media invariably miss this point. Simply looking at fossils will not provide us with foolproof answers about ascent and descent.

Here the author states that since our imagination is influenced by things around us, it is difficult to arrive at correct conclusions by examining fossils, because they can take forms that defy our imagination. Palaeontologists often struggle with inadequate search images in their attempt to make sense of what they see in the fossil world. If evolution is a fact of life, all that we can assume is that all organisms that live today - and those that ever lived in the past - must have a single common ancestor. But ``Deep Time'' is not the medium suited to tell our stories of evolutionary history to dovetail into our pre-existing prejudices.

Coming to the question of evolution of humanity we know that palaeontologists have always flocked to East Africa in search of fossils because this part of the world boasts of a rich fossil heritage caused by a geological accident, the Great Rift, that happened in the right geological time frame. The search for human origins in the Rift is synonymous with the name of Leakey; Louis and wife Mary, Richard, wife Meave and daughter Louise. Although fossil hunting depends on a slice of luck, it also calls for a good search image telling the palaeontologist what he wants to find. Given what the Leakeys and others have found in East Africa, it is reasonable to assume that hominids lived in the Rift before they lived anywhere else.

Thus we have reasons to believe that our ancestry can be traced back to creatures that lived between three and five million years ago in the Rift. However, despite all the back-breaking work that the anthropologists have put in, there still is much grey area. The time interval between three and five million years in the past has divulged fossils left behind by several hominid species. Homo sapiens date back to 200,000 years ago in Africa and the mitochondrial DNA, which is passed on to the succeeding generation only by the mother, should take us back to one prehistoric woman, the mitochondrial eve, who probably lived 200,000 years ago from whom all mitochondrial DNA stemmed. Yet, this woman, in all likelihood, was not alone. She was perhaps a member of a clutch of women of her time. Further analysing our own grandiose perceptions of our special place in the evolutionary tree, the author raises several queries: can our brain volume be considered as a benchmark separating humans from non-humans? Perhaps not; yet palaeontologists have used this as a qualitative measure responsible for the development of superior intelligence. Some of the other attributes regarded distinctively human are the ability to make and use tools, bipedality and language. The author examines each one of them and shows how erroneous these conclusions could be. Modern evolutionary biology is based on a set of hypotheses created by Charles Darwin which forms a body of work which he called ``natural selection'', a process of winnowing, as the author puts it. These hypotheses could be tested and, in due course, gave rise to more hypotheses which Darwin could not have imagined in his time. Many decades after Darwin published his Origin of Species geneticist Dobzhansky discussed natural selection in his book Genetics and the Origin of Species and pointed to a synthesis of genetics and evolution. Here the author lays emphasis on how much evolution of life has been a response to the contemporary ecological context. We know many creatures that are alive today that influence the lives of their fellow beings. Many of them like the roundworms and nematodes do not even fossilise. Therefore, what we glean from the fossil records about past life stands the risk of being divorced from their contemporary ecological context.

Fossils, says the author, are imperfectly preserved fragments which a palaeontologist interprets in the light of modern models that often lead to conclusions to suit pre-existing stories about ancestry and descent. In another context the author states how, in the absense of fossils, it is still possible to read this history of species from a study of molecules, or more specifically, the DNA. In 1998 a team of researchers from the University of Edinburgh actually achieved this in the case of the parasitic roundworm and presented the first ever cladogram of roundworms. This line of work can lead to profound research projects like trying to find a cure for AIDS for example.

There is lot more in this book: whether fish evolved legs to crawl on land or to get quickly under water, how dinosaurs evolved feathers long before they became birds, whether some dinosaurs could have been the dragons that fell to the Earth and so on. The author concludes the book by sparing a thought for the present state of humanity which is at a crossroads, on the verge of moving into space. Our steps in this direction are still tentative but we have all the time in the universe at our disposal. One day, some millions of years into the future, one of his descendants, says the author, may visit the home planet and pick up in its hands or tentacles or whatever, a fossil left behind by the author and begin to wonder whether this fossil belonged to one of its distant ancestors. But it will have no way of knowing one way or the other.

C. V. SUBRAMANIAM

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