Science: Darwin updated

It seems that key genes can bring about sudden, huge changes in body form - and may account for `missing links' in the evolution of species.

Ronald Reagan is the missing link" proclaims a vintage American lapel badge. It's the kind of joke that scientists appreciate, even now, for its teasing acknowledgement that biological puzzles can often have political significance. The mystery of "missing links" is about what sense to make of the gaps in the fossil record between fish and fowl, or ape and early human. It remains a conundrum 140 years after Charles Darwin first tried to explain it away.

Jeffrey Schwartz, an American evolutionary biologist, claims to have developed a radical new theory that can account for those embarrassing gaps, which are regularly exploited by creationists in the US to try to undermine the intellectual foundations of evolutionary theory. Yet paradoxically, with the publication of his new book - Sudden Origins: Fossils, Genes, and the Emergence of Species - Professor Schwartz could stand accused of providing aid and comfort to the enemy camp. Already, anti-evolutionary groups are citing his book as evidence that even scientists don't agree about evolution. In his mid-fifties, and a respected professor of anthropology at the University of Pittsburgh, Schwartz is bemused: "I said to my wife, wouldn't it be ironic if I sold 50 000 copies to creationists?"

In fact, Schwartz's views on evolution "throw a huge monkey-wrench into the creationists' argument," he says. Anti-evolutionists have long claimed the gaps as evidence that God made each of the millions of species that have lived on Earth in repeated acts of special creation. "There are gaps in the fossil record," Schwartz agrees, "but they do not threaten the idea of the evolution of species." According to Schwartz, "the fact that we don't find intermediate forms between fish with fins and land animals with legs is no big deal; we shouldn't be frightened by it." In fact, it is a mistake to expect such half-way houses, he argues.

Apes have big toes that stick out to the sides, while human toes are all aligned side by side. Palaeontologists scour the land for fossil remains to fill that gap, and show signs of an ape-human with a half-way straight toe, but will never find them, says Schwartz. He thinks that walking upright on two legs was probably an abrupt, all-or-nothing sort of innovation. "When novelties arise, they arise suddenly, without a trail of intermediaries," he insists.

Schwartz calls himself a "non-Darwinist", though not an "anti-Darwinist". He's non-Darwinian because he removes Darwin's mechanism of natural selection from the driving-seat of evolution. He argues that new species do not originate through the gradual accumulation of tiny mutations, each favoured by natural selection for their adaptive qualities, as Darwin proposed.

Instead, Schwartz says, new species can appear suddenly; novel organs and lifestyles can arise virtually overnight. A fish's fins turn into limbs, partially equipping it for a life on land, while teeth erupt in a hitherto toothless fish's jaw. Even eyes can pop out of nowhere. "Richard Dawkins's idea that an eye evolves slowly over countless generations through the painstaking accumulations of tiny mutations - that's wrong," says Schwartz.

His argument relies crucially on the special powers of what are known as homeobox genes. In a fruit fly a small molecular change in one of these genes can produce an effect as profound as having or not having an eye. These genes can wield such power because they play a regulatory role; they influence key decisions during the development of embryos.

For instance, a slight variation in one of these genes can turn an embryonic limb bud into either a fin or a foot, either an arm or a wing. Another homeobox gene, Hoxd-13, controls the size of bones in the wrist, finger ankle and toe; perhaps a mutation in this key gene produced the modern horse, balanced on hooves that are enlarged single toes. "Development is like a whole set of dominoes lined up on end," says Schwartz. "Tip one over and you set off a cascade of effects. Similarly, change a regulatory message at the beginning of a developmental pathway and you can generate profoundly different results."

Most studies of genetic differences between species have focused on structural genes, responsible for making straightforward protein products used as enzymes or body-building material. What's so striking about the regulatory homeobox genes is that many are broadly similar in organisms as distinct as flies and human beings. "Who would have thought that a squishy worm, a hardened-cuticle-encased fruit fly, and an internally bone-supported human shared similar body-shaping regulatory molecules?" Schwartz asks.

It's not so much the genes per se, but what they do, that matters. "It is mind-boggling to realise that, for all intents and purposes, many differences between a fruit fly and a human being may lie pretty much in where and when certain homeobox genes are activated," says Schwartz. "To be sure, there are some others... But, fundamentally, the main difference between organisms lies in alterations in development that result from differences in the timing of homeobox gene activity."

In a way, it makes no sense to talk of genes for a worm or genes for a human being, he argues. "Rather, particular combinations of the genes that are already present in all organisms lead to the development of organisms with distinctive body shapes and functions." So new species arise not through the gradual accumulation of minor changes in scores of genes, says Schwartz, but through changes in the action of one or just a few homeobox genes.

This notion has radical implications for our species' own family tree. In the Eighties, Schwartz proposed that, on anatomical grounds, orang utans should be regarded as more closely related to human beings than are chimpanzees or gorillas. Yet later genetic studies of structural genes put chimpanzees as our closest living relatives. Who is right? Until we can analyse the action of key regulatory genes, says Schwartz, the answer remains open.

Strange goings-on in homeobox genes could also shed light on the origins of "weird" animals such as whales and sloths. Subtle changes in regulatory genes could explain why these animals appear "so different, so much more uniquely themselves", obscuring their real evolutionary relationships. "If a mutation led to your developing wheels on the top of your head," suggests Schwartz, struggling for a bizarre example to make his point, "you'd be like no other species, but you'd still be Homo sapiens' closest relative.

"Non-stop discoveries in developmental genetics are making it eminently clear that we must expand our vision of evolution, and of evolutionary processes," he says.

`Sudden Origins: Fossils, Genes and the Emergence of Species', by Jeffrey Schwartz (Wiley, pounds 22.50)

Suggested Topics
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment

ebooksNow available in paperback
Arts and Entertainment

ebooks
Arts and Entertainment
Feeling all at sea: Barbara's 18-year-old son came under the influence of a Canadian libertarian preacher – and she had to fight to win him back
TV review
Arts and Entertainment
Living the high life: Anne Robinson enjoys some skip-surfed soup
TV review
Arts and Entertainment

Great British Bake Off
Arts and Entertainment
Doctor Who and Missy in the Doctor Who series 8 finale

TV
Arts and Entertainment

film
Arts and Entertainment
Chvrches lead singer Lauren Mayberry in the band's new video 'Leave a Trace'

music
Arts and Entertainment

music
Arts and Entertainment
Home on the raunch: George Bisset (Aneurin Barnard), Lady Seymour Worsley (Natalie Dormer) and Richard Worsley (Shaun Evans)

TV review
Arts and Entertainment

TV
Arts and Entertainment
Strictly Come Dancing was watched by 6.9m viewers

Strictly
Arts and Entertainment
NWA biopic Straight Outta Compton

film
Arts and Entertainment
Natalie Dormer as Margaery Tyrell and Lena Headey as Cersei Lannister in Game of Thrones

Game of Thrones
Arts and Entertainment
New book 'The Rabbit Who Wants To Fall Asleep' by Carl-Johan Forssen Ehrlin

books
Arts and Entertainment
Calvi is not afraid of exploring the deep stuff: loneliness, anxiety, identity, reinvention
music
Arts and Entertainment
Edinburgh solo performers Neil James and Jessica Sherr
comedy
Arts and Entertainment
If a deal to buy tBeats, founded by hip-hop star Dr Dre (pictured) and music producer Jimmy Iovine went through, it would be Apple’s biggest ever acquisition

album review
Arts and Entertainment
Paloma Faith is joining The Voice as a new coach

TV
Arts and Entertainment
Dowton Abbey has been pulling in 'telly tourists', who are visiting Highclere House in Berkshire

TV
Arts and Entertainment

TV
Arts and Entertainment
Patriot games: Vic Reeves featured in ‘Very British Problems’
TV review
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
SPONSORED FEATURES

ES Rentals

    Independent Dating
    and  

    By clicking 'Search' you
    are agreeing to our
    Terms of Use.

    Migrant crisis: UN official Philippe Douste-Blazy reveals the harrowing sights he encountered among refugees arriving on Lampedusa

    ‘Can we really just turn away?’

    Dead bodies, men drowning, women miscarrying – a senior UN figure on the horrors he has witnessed among migrants arriving on Lampedusa, and urges politicians not to underestimate our caring nature
    Nine of Syria and Iraq's 10 world heritage sites are in danger as Isis ravages centuries of history

    Nine of Syria and Iraq's 10 world heritage sites are in danger...

    ... and not just because of Isis vandalism
    Girl on a Plane: An exclusive extract of the novelisation inspired by the 1970 Palestinian fighters hijack

    Girl on a Plane

    An exclusive extract of the novelisation inspired by the 1970 Palestinian fighters hijack
    Why Frederick Forsyth's spying days could spell disaster for today's journalists

    Why Frederick Forsyth's spying days could spell disaster for today's journalists

    The author of 'The Day of the Jackal' has revealed he spied for MI6 while a foreign correspondent
    Markus Persson: If being that rich is so bad, why not just give it all away?

    That's a bit rich

    The billionaire inventor of computer game Minecraft says he is bored, lonely and isolated by his vast wealth. If it’s that bad, says Simon Kelner, why not just give it all away?
    Euro 2016: Chris Coleman on course to end half a century of hurt for Wales

    Coleman on course to end half a century of hurt for Wales

    Wales last qualified for major tournament in 1958 but after several near misses the current crop can book place at Euro 2016 and end all the indifference
    Rugby World Cup 2015: The tournament's forgotten XV

    Forgotten XV of the rugby World Cup

    Now the squads are out, Chris Hewett picks a side of stars who missed the cut
    A groundbreaking study of 'Britain's Atlantis' long buried at the bottom of the North Sea could revolutionise how we see our prehistoric past

    Britain's Atlantis

    Scientific study beneath North Sea could revolutionise how we see the past
    The Queen has 'done and said nothing that anybody will remember,' says Starkey

    The Queen has 'done and said nothing that anybody will remember'

    David Starkey's assessment
    Oliver Sacks said his life has been 'an enormous privilege and adventure'

    'An enormous privilege and adventure'

    Oliver Sacks writing about his life
    'Gibraltar is British, and it is going to stay British forever'

    'Gibraltar is British, and it is going to stay British forever'

    The Rock's Chief Minister hits back at Spanish government's 'lies'
    Britain is still addicted to 'dirty coal'

    Britain still addicted to 'dirty' coal

    Biggest energy suppliers are more dependent on fossil fuel than a decade ago
    Orthorexia nervosa: How becoming obsessed with healthy eating can lead to malnutrition

    Orthorexia nervosa

    How becoming obsessed with healthy eating can lead to malnutrition
    Lady Chatterley is not obscene, says TV director

    Lady Chatterley’s Lover

    Director Jed Mercurio on why DH Lawrence's novel 'is not an obscene story'
    Farmers in tropical forests are training ants to kill off bigger pests

    Set a pest to catch a pest

    Farmers in tropical forests are training ants to kill off bigger pests