The other evolutionaries
DARWIN BICENTENARY: 1809-2009:Remarkable Creatures: Epic Adventures in the Search for the Origin of Species, by Seán B. Carroll, Quercus, 331pp, £16
SEÁN CARROLL, Irish by descent, has written about Darwin and the adventures, both intellectual and physical, of some of those who helped to verify the Theory of Evolution. In 1859, Charles Darwin described how evolution occurred, throwing light “on the origin of man and his history”. Carroll’s book mostly tells us about other scientists who showed Darwin was right.
A professor at the University of Wisconsin, a strong centre for genetics, Carroll is well known for his studies in “evo-devo” – what can we learn about evolution by studying the development of embryos? His authority is delightfully lightened by a talent for storytelling. He writes: “We took a lot longer than our neighbours to finish dinner, something my mother is very proud of to this day”.
This story is peppered with journeys to exotic places where scientists, mostly young, made astonishing contributions to biology. The book should be read by all who marvel at the natural world, and would make a suitable present for any inquisitive student from 16 onwards who shows the slightest interest in biology.
Each chapter, with one or a few heroes, tells of a major breakthrough. First we have Alexander von Humboldt describing his discoveries in South America in 30 volumes, and inspiring the young Darwin. Then, just one chapter on, Darwin, who moves biology from theology to science and inspires everything that follows, we read of Alfred Wallace, who had nearly died collecting in Amazonia, and then lost all his specimens when his ship home caught fire and sank in mid-Atlantic. Wallace promised never to leave England again, but quickly set off for the East Indies, where he dodged tigers in Singapore and head-hunters in Borneo. In 1858, while afflicted by a severe bout of malarial fever, he discovered natural selection independently of Darwin. Carroll is very fair to Wallace and the book will help to advance Wallace, and his other discoveries, in the public imagination.
Henry Bates, Wallace’s companion in South America, stayed on and discovered Batesian Mimicry, the tendency of non-poisonous to mimic poisonous creatures under natural selection and so avoid predators. Eugène Dubois, a young and hugely talented Dutch doctor, gave up medicine and, with his new family, went in search of our ancient ancestors in the East Indies. He dug up a few bones of Java Man in 1890, helping to bridge the gap “twixt ape and Plato”. Now known as Homo erectus this creature caused a huge controversy and suggested that Homo sapiens had evolved in Asia, not Africa as Darwin suspected.
Other intrepid fossil hunters are introduced who scoured the globe and found missing links, between dinosaurs and birds, between fish and four-legged creatures who could walk on land. The extraordinary father-and-son team of Nobel chemist Luis Alvarez and geologist Walter, are introduced; they explained in 1980 how the dinosaurs were made extinct after an asteroid smashed into our planet 65 million years ago, the dust darkening the earth for thousands of years.
The story returns to the prehistory of man and the stage shifts to Africa in 1917. A 14-year-old boy in Tanzania, the son of a missionary, has been brought up as a Kikuyu.
He collects fossils and ancient tools and gives them to the museum in Nairobi. The boy, Louis Leakey, graduates from Cambridge and spends the rest of his life fossil hunting in Africa, in partnership with his wife, Mary, and their son, Richard.
In the 1960s she is directing the excavations and he is giving lectures around the world which sell out weeks in advance. I remember his lecture at the California Institute of Technology had to be retransmitted, with sound only, to a dismal hall, where we were enthralled. The Leakeys had found many man- and ape-like fossils, they had shifted the origin of man to Africa – Homo habilis at 1.4 million years was older than Homo erectus. The African fossils suggested that man and apes had diverged about 30 million years ago – this estimate was soon challenged “from left field”.
In 1959, chemists Linus Pauling and Emile Zuckerkandl, at Caltech, invented a new molecular method of dating ancestors; they calculated that the common ancestors of man and a gorilla lived about 11 million years ago.
Leakey and others reacted vehemently to the interlopers from chemistry. But Allan Wilson at Berkeley produced more molecular evidence that humans diverged from chimps and gorillas about seven and 12 million years ago respectively. In 1987, he proposed that all modern humans had a common ancestral group which lived in Africa about 150-200,000 years ago, now widely accepted.
Svante Paabo is today completing the genome sequence of the extinct Neanderthal Man. Neanderthal is our closest known relative and lived with us in Europe until 30,000 years ago. Man diverged from Neanderthals about 500,000 years ago, and there is no evidence from the genome data – where we could have seen it – that man interbred with Neanderthals.
This is a rattling good tale. Darwin was right. Man is an ape, more closely related to chimps than chimps are to monkeys. How would we view Neanderthals if they had survived till today? Did they speak? Carroll muses on why they went extinct.
- David McConnell is professor of genetics at Trinity College, Dublin. He will give the Darwin Day Lecture in the Davis Theatre in Trinity on February 12th at 7.30pm