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‘Why,’ a physicist colleague once asked me, ‘do lizards, frogs and dogs
and their kin always have four legs – never six, say, like insects?’ Just
the kind of peculiar question a nonbiologist would ask, I thought to myself.
‘It’s just one of those things,’ I replied, stalling for time. ‘The ancestor
of vertebrates just happened to have four.’ Then I threw in: ‘I don’t ask
you why there are nine planets in the Solar System, do I?’

For years, this instance of intellectual bad faith has niggled away
in the back of my mind. Then I met Keith Thomson, ichthyologist, palaeontologist
and author of a new book on that most famous of ‘living fossils’, the coelacanth.
I apologetically dredged up the physicist’s question. ‘I have the answer,’
Thomson said in a rush. ‘Or at least I think I do. It’s because we’re all
´Ú¾±²õ³ó±ð²õ.’

Fishes swim by curving their bodies into a sine wave, which creates
four places of maximum force – at the spots where, sensibly, the fins are.
He drew a quick sketch to show that six fins would form an unworkable sine
wave and a half; eight fins are possible, but would require an impracticably
long body that could contort through two sine waves.

Thomson is ‘the sort of person who keeps science afloat, well afloat’,
says an old friend, Humphrey Greenwood of London’s Natural History Museum.
Thomson loves puzzles, and unlike me, never tries to forget about them.
Yet he escapes the self-absorption that might go with a ferocious appetite
for finding answers. ‘It’s all right if you don’t inhale,’ he says about
life in general; ‘Take a subject seriously, but not yourself.’

Having lived in both Britain and the US has heightened his instinct
for standing back and taking a fresh look at things. Growing up in Leicestershire,
Thomson made his career in the US, mostly at Yale University. But he didn’t
join Britain’s brain drain by choice. After reading zoology at Birmingham,
and falling in love with fishes during a vacation studentship with Greenwood
at the Natural History Museum, he was advised to go to Harvard to study
under the eminent palaeontologist Alfred Sherwood Romer.

Despite a two-year postdoc at University College London, he could find
no way back. ‘Once you’re out of the system, the network of contacts, it
is very difficult to get back in,’ he said. ‘And there were zero jobs in
evolutionary systematics in Britain then – and that is still sadly the case.’

He returned to America to lecture at Yale and stayed for 22 years, relishing
both the teaching and the research. The fashionable notion of splitting
research and teaching in British universities fills him with horror. ‘Some
of my best ideas have came from interacting with students.’ He cited as
an example his theory about how sharks swim. ‘I was trying to teach the
received wisdom to students, and they couldn’t understand. I suddenly realised
that it didn’t make sense.’

The value of his chosen field – the study of how whole animals work
and have evolved – he also vigorously defends. ‘So-called stuffy systematics
is the basis of everything: biology is at its core a comparative science,’
he says. ‘That’s why the furore about the Natural History Museum is so important,’
he argued. Biodiversity is a media buzzword, but conservation schemes rely
on people who can recognise and study the millions of living organisms on
Earth. ‘As universities abandon systematics, the world’s great museums are
the only place left with this expertise.’ A whole field of human knowledge
is in danger of extinction, Thomson fears.

In his new post, as president of America’s oldest natural history museum,
the Academy of Natural Sciences in Philadelphia, Thomson is well placed
to battle on in its defence. Like any human activity, ‘science is intensely
political,’ he said. ‘It is a deadly game. You have to play it or be swept
aside.’ Systematics has floundered because scientists in the field ‘allowed
other people – molecular biologists in particular – to capture the intellectual
high ground’.

Thomson’s latest book, Living Fossil (Hutchinson Radius), is a delightful
account of the personalities and politics surrounding the discovery of a
live specimen of the fish everyone thought died 70 million years ago. Into
the story he deftly weaves entertaining accounts of how the creatures evolved
and where and how they might live today. Specialists in the field may find
niggling inaccuracies; Thomson wrote without the benefit of a new monograph
on the species just published. But such details are of no significance to
the general reader, and Thomson’s book deserves to become a classic example
of the best in popular science writing.

What role does Thomson see himself as playing? After an uncharacteristic
pause, he laughed: ‘I suppose I am trying to be the person I admire from
the 1920s and 1930s when science and arts weren’t so divided as they are
now.’ He comes close, I think: it is rare these days to find anyone to whom
the tag ‘Renaissance man’ applies in the slightest. In Thomson’s home, non-science
books outnumber science books by a ratio of 20:1, ‘which is how it should
be’, he said. He attributes his enduring marriage to the fact that his wife,
an artist, ‘has not the least interest in science, so I never talk shop
at home’. As he left our office, he was off to see the new pop art exhibition.