Jack Homer has a vision. A world-famous paleontologist who gives "an awful lot of lectures," Horner pictures himself strolling out on stage before a crowd, just as he's done countless times before. Instead of carrying the standard sheaf of notes or dusty slides, though, he has with him the ultimate prop: a real live dinosaur on a leash. "It's small, but bigger than a chicken," he writes in his new book, How to Build a Dinosaur. "Let's say the size of a turkey, one day maybe even the size of an emu." The emu-size dinosaur, he adds, "might have a muzzle or a couple of handlers."
If it sounds straight out of Jurassic Park, it's no coincidence: Homer served as scientific advisor on all three films, and is said to be an inspiration for the rugged protagonist, Alan Grant. Unlike in the movie, though, Homer thinks he can bring back a dinosaur without using its DNA--a crucial difference, because in real life, dino DNA hasn't been recovered. Homer has a different plan. By making a few genetic tweaks to its modernday ancestor, the bird, he wants to hatch a dinosaur straight from a chicken egg.
It's Horner's vision, and McGill University paleontologist Hans Larsson is working to make it happen. With Homer's encouragement, Larsson is experimenting with chicken embryos to create the creature Horner describes: a "chickenosaurus," they call it. If he succeeds, Larsson will have made an animal with clawed hands, teeth, a long, dinosaurian tail and ancestral plumage, one that shares characteristics with "the dinosaur we know that's closest to birds, little raptors like the velociraptor," Homer says.
Their quest to build a dinosaur is taking them millions of years into the past, and forward again to the very edge of science, so cutting edge it sounds more like science fiction. Beyond the ethical questions that surround their work--or even practical questions, such as how and where such a creature would live--resurrecting a dinosaur sounds too far-fetched to be true. Yet both men insist they're almost there. "I believe it will happen," Larsson says. It's just a question of when. If all goes according to plan, he adds, Horner will have his pet dinosaur within five years' time.
Reached over the phone at the T.rex Discovery Centre in Eastend, Sask. (otherwise known as "Dino Country"), Larsson has been out in the field all week, digging for bones. As part of a three-week course he teaches in paleontological fieldwork, 15 students, mostly from McGill, spend their days prospecting through the badlands, excavating fossils with anything from "dental utensils to a pickaxe and shovel." At night, they gather round a bonfire, sharing beers and stories. There's much to tell: one student found a velociraptor claw; another got a Tyrannosaurus rex's tooth. "We finished [digging out] a baby T. rex skull last week," says Larsson, 38.
Compared to his lab work with chicken embryos, digging up dusty bones seems decidedly old school. Yet Larsson, one of the very few paleontologists who also works with embryos, insists they're intimately linked--which brings him to Saskatchewan, a great place to look for fossils. The reason why dates back about 66 million years, when a meteor "the size of Montreal island" smashed down near Mexico's Yucatan Peninsula, sparking forest fires, tsunamis, and sending up a giant dust cloud that spread throughout the atmosphere. "Seventy-five per cent of all species went extinct," Larsson says. "Most life ceased." Eventually, the debris settled, creating a clay layer that's still visible at different locations across the planet, including in Saskatchewan, where it's a "beautiful, one-cm-thick orange clay, packed through with shocked quartz and iridium."
Because the baby T. rex skull was found near the clay layer, it was probably one of the last dinosaurs to live before the mass extinction. According to Larsson, a creature's evolution over millions of years--which can be traced in fossils like the T. rex skull--provides valuable insight into the individual animal's development over its lifetime. Likewise, a chicken's progress from embryonic blob to feathered fowl says something about evolution, and maybe even how to reverse it.
It's a driving idea behind evolutionary developmental biology, or "evo devo" for short. A relatively new field of science, evo devo was sparked by the startling discovery that most creatures share many of the same genes. Homeobox genes (or Hox genes), which flick on during development and govern which body parts go where, were first found in fruit flies in the 1980s, says Sean Carroll, an evolutionary biologist at the University of Wisconsin-Madison. (Experiments to find Hox genes were straight out of a horror movie: scientists treated insects with legs where their mouths should be.)
After pinpointing these master genes, researchers "looked around the animal kingdom, and were stunned and delighted to find them everywhere," Carroll says. Indeed, we've got more in common with other species than most people realize. The DNA of a person and a chimpanzee, for example, are about 99 per cent identical--meaning that, in the six million years of evolution that divide us, less than one per cent of the three billion letters in the human genome have changed. Even the sea squirt, a tube-shaped creature that clings to underwater piers, shares about 80 per cent of our genes. "If you take snakes, frogs and birds, you're really taking the same genes and using them in different ways," Carroll says. Not only do we share genes with other animals; we share them with distant ancestors, too. Despite evolutionary change, many of our genes have been around for more than 500 million years, Carroll says.
Three years ago, evolutionary biologist Nell Shubin unveiled one of the most significant fossil finds of the century: Tiktaalik, a 375-million-year-old fish with "a neck, elbows, shoulders, even proto-wrists," he says. An almost perfect link between fish and land vertebrates, Tiktaalik (unearthed in Nunavut) is our own distant cousin.Just as Larsson looks to dino bones to understand his embryos, Shubin used the fossil to design an experiment with modern-day paddlefish. He found that, even before limbed animals evolved about 365 million years ago, fish had the genes necessary to grow arms and legs. "Evolution doesn't always rely on the development of new genes" Shubin explains. "It's redeploying old genes in new ways: changing their switches, or their time of activity."
By tripping the right genetic switches at the fight time, then, Larsson should be able to build a dinosaur inside a chicken egg.
While Larsson tinkers with the embryos in his lab, other scientists are on the hunt for dinosaur DNA, the so-called blueprint for life. In the movie Jurassic Park, researchers manage to extract it from a mosquito trapped in amber, then implant it into a frog's egg; not long after, the park is swarming with velociraptors, triceratops, and even a bloodthirsty T. rex.
Harvesting DNA from bugs in amber worked just fine in the movies, but in real life, it hasn't panned out. "Many people have tried, myself included," says Blair Hedges, an evolutionary biologist at Pennsylvania State University, who says a sample could provide invaluable information on everything from a dinosaur's appearance and behaviour, to the process of evolution. It could also theoretically be used to build a dinosaur, if enough were recovered--the first step, though, is to find some. So far, the oldest DNA ever recovered is under one million years old. The last dinosaurs died out 65 million years ago.
It isn't necessarily the passage of time that ruins a DNA sample, so much as its surroundings, says Hendrik Poinar, director of McMaster University's Ancient DNA Centre. Heat and humidity, for example, are both known to break down the molecule. "There's no environment I can think of that would have remained constant enough to preserve dinosaur DNA," he says. But "despite the fact I'm a disbeliever, I'm still a scientist. If you can find a bone that's been in some weird cave for 65 million years, give it a shot."
Finding that "weird cave" might not be so improbable. In 2005, Mary Schweitzer, a paleontologist at North Carolina State University, made an astonishing announcement: she'd discovered soft tissues in the leg bone of a 68-million-year-old T. rex. Her findings were, of course, controversial; yet in May, Schweitzer repeated the trick, this time with an 80-million-year-old hadrosaur. (The duck-billed dinosaur was sealed in dry, porous sandstone, which seemed to help with preservation.) "People just assume these tissues degrade," she says, and because of that assumption, "no one bothered to look."
None of Schweitzer's soft tissues and proteins have so far yielded any dino DNA, but the discovery alone is enough to give hope. If these tissues can survive, Schweitzer suggests, maybe DNA can, too.
And if sandstone is a good preservative, so is the Arctic deep freeze. Each year in Siberia, the tusks, teeth and bones of ancient woolly mammoths (an elephant species extinct for over 4,000 years) can be found along the coast, shaken loose by erosion and the summer thaw. Mummified carcasses have even been uncovered, including one named Lyuba, a near-complete baby mammoth found in western Siberia in 2007. All of these, of course, could be rich sources of DNA.
Last year, researchers at Pennsylvania State University announced they'd managed to map 70 per cent of the woolly mammoth genome, the first time an extinct animal's genome had been sequenced. The feat was accomplished using DNA from the hair of a 20,000-year-old mammoth found buried in the Siberian permafrost. Hair proved to be a great source, says Webb Miller, a professor of biology and computer science who worked on the project. "It locks out moisture and bacteria," he says. "We just basically dunk it in bleach, open the hair shaft and take the DNA out." Not only that, hair is easy enough to get: "Woolly mammoths have lots of it. We could literally buy pounds, if we wanted to."
Miller hopes the genome will provide a wealth of information on what drove the woolly mammoth to extinction, a puzzle that hasn't yet been solved. "I would sleep easier if I knew that whatever wiped out this species," whether it's a disease, climate change, or something else entirely, "won't happen to us," he says. And of course, having the roammoth's genetic map offers up the tantalizing possibility of resurrecting the iconic animal--something Miller thinks is inevitable.
Last fall, a group of Japanese scientists announced they'd cloned healthy mice from dead ones frozen up to 16 years, leading one to suggest that bringing back a frozen woolly mammoth was "no longer science fiction." To clone an extinct animal, scientists would theoretically need its entire coding sequence, Poinar says. Since we currently have only 70 per cent of the mammoth genome, they'd have to create a hybrid at first, tweaking an elephant genome to create a modified mammoth genome. The modified genome would then be injected into an embryonic cell and implanted into an elephant, which would carry the baby to term.
While dino DNA has been elusive, that of less-distant creatures has been recovered; and so mammoths aren't the only candidates for resurrection. Researchers at the Max Planck Institute for Evolutionary Anthropology in Germany recently announced they'd mapped the genome of the Neanderthal, a human species extinct for 30,000 years; not long after, Harvard University genetics professor George Church suggested in the New York Times that a Neanderthal could be brought to life for about $30 million. Poinar's group at McMaster is sequencing the genome of the mastodon, an ancient type of elephant with long, reddish hair. Other groups are mapping genomes for the Tasmanian tiger and the New Zealand moa (a large flightless bird), to name a few.
When it comes to bringing these creatures back from the dead, "there's no question we will be able to do it, and it will be done," Poinar says. "The big question," he adds, "is should it be done?"
Out on the grassy lawn at the University of Toronto's Scarborough campus, where a zoology conference is being held, Larsson removes a fat test tube from his leather bag. In it floats a chicken embryo, curled upon itself, its cartilage stained an unearthly blue. Less than half as big as a human thumb, the specimen is almost unrecognizable, and not just because of its sharp hands and feet, or its two wide, empty eyes. The embryo's delicate spine--when the sunlight shines down through the test tube, each tiny vertebrae is visible--continues well past its backside, creating a thick and pointed tail. Fully developed chickens, of course, don't have tails.
It's one of the basic principles of evo devo: as an embryo morphs from just a few cells into a fully formed creature, it shows echoes of ancestral traits, bumping up against evolution along the way. Chicken embryos, for one, start off looking fairly generic, much like the fishy ancestor they share with humans and other vertebrate creatures (it was in the fish that nature first learned how to lay down a backbone, Carroll says). As the embryo continues to transform, there's a brief window when, according to Larsson, it takes on 'dinosaurian traits." For a mere 10 hours, the chicken embryo sprouts five fingers with pointed and clawlike tips, a hint of teeth, and a tail (up to 22 vertebrae, roughly 15 more than in a developed chicken). Suddenly, a genetic switch flips: the teeth disappear, the tail is destroyed, and the five fingers become three. It looks much more like a bird.
Why would an embryo build extra fingers, teeth or a tail, only to have them disintegrate? Evolutionary change is "like tuning a car while the engine's running," Carroll says. "You can't just junk one part and put something else in; in the meantime, it wouldn't work. Those pre-existing programs are often the foundation for something new." For Larsson, the trick will be to override them.
The first step is figuring out the normal process of chicken development, "so we don't develop a mutant chicken that has nothing to do with development or evolution," he says. (Think of mothers who took thalidomide, a drug used to treat morning sickness in the 1960s, many of whose babies were born with flipper-like hands and feet.) Experiments can be as simple as injecting fluorescent dyes into the embryo, to trace which cells move where. Its progress would then be lined up with the fossil record, which shows, for example, the transition from a fat dinosaur tail to the bird's stumpy pygostyle: the T. rex had 35 vertebrae; Archaeopteryx, an intermediate creature, had 25; a full-grown chicken has up to eight.
In the lab, Larsson's also working with transplants, clipping the tip of a chicken embryo's tail and clamping it onto another "when the tail is about to shut down, to see if we can rescue it." In the best cases so far, it grafts on but keeps its own genetic program instead of kickstarting the embryo's, which is the goal. Larsson's even tried taking tail tips from 20 embryos, combining them into a "big ball of cells" to make an implant that might activate the tail. He's working with drugs, too, but "we still have to find the right pathways," he says. Pharmaceuticals haven't helped with tail growth so far. "We get bizarre things," he says. "It almost looks like you took a hammer and crushed it."
Even so, drugs have shown some promise in saving the embryo's tiny forearms. Larsson has also managed to produce one specimen with a couple of extra vertebrae. And a few years ago, scientists from the Universities of Wisconsin and Manchester discovered a mutant chicken with a complete set of teeth, an ability that was lost in birds about 100 million years ago, suggesting they can be developed, too (the mutant died before it could hatch). The work is still mostly trial and error, but "we're getting closer," he says.
If his efforts succeed, what will Hans Larsson have created? "Within five years, I think we could get a chicken with a tail, forearms, and teeth, and transform its feathers back to their ancestral shape, which is probably a hollow quill," he says. It would be slightly larger than a standard chicken, although using another bird species (say, an emu) or treating it with growth hormones could produce different results. It would still have a chicken genome, and so wouldn't technically be a T. rex or a velociraptor; but it wouldn't be a chicken, either, at least not as we'd recognize it. So what, exactly, would it be?
"It would be a dinosaur," Larsson says, "because chickens are dinosaurs."
Fly a helicopter across the Siberian permafrost, and look down at the open spaces below. "You can just close your eyes, and see herds of woolly mammoths walking across it," Hendrik Poinar says. As a child, he dreamt of seeing the mammoth, a woolly rhinoceros or even a sabre-tooth tiger in the flesh, instead of just in his history books. "You can't help but be fascinated at the possibility of laying your eyes on something as iconic as that." It's easy to get swept up in the excitement, but Kerry Bowman, a bioethicist at the University of Toronto, urges a note of caution. "Jurassic Park was a really fun movie," he says, "until the dinosaurs got loose."
Of course, Bowman's speaking in metaphor: not much threat would be posed by a turkey-sized chickenosaurus, even if one flew the coop. In his book, Homer notes that if his dinosaur escaped, it would have about the same chance of survival as a lone chicken. "If by some miracle it did mate with a hen or rooster," he writes, "the result would be an old-fashioned chicken. If it died, we could stuff it and roast it. It would taste, as the proverb says, like chicken."
Sounds harmless enough. Beyond the chance such a creature could escape, though, Bowman says we need to "take a deep breath" before tinkering with animal life. With the mammoth, "knowing elephants, I can only imagine these are highly sophisticated, social and sentient creatures," he says, adding that, if one were created, it would likely be in isolation. Bringing back a Neanderthal, of course, would be even more fraught. "What would its moral status be?" asks Bowman, who is also president of the Canadian Great Ape Alliance. As our own sibling species, "would it be housed in a zoo? Would it be treated as a low-functioning human?" Would it be closer to an ape, or to a person?
Even Poinar, who collaborated on the woolly mammoth genome project, questions the merits of actually creating one. "Typically there's a drive in science to do something, just to say you've done it," he says. "There is no scientific benefit to bringing back an extinct species like [the mammoth], that I can think of. You're creating a biological curiosity that's going to sit in a zoo, or even a theme park. To me, that is sad enough."
But for Jack Horner, making people stare is exactly the point. The chickenosaurus will be a conversation piece, he says, sparking a public debate about evolution by winding its tape backwards for all to see. "Let's put it this way," Homer says. "You can't make a dinosaur out of a chicken, if evolution doesn't work."
Source Citation:Lunau, Kate. "The quest to build a dinosaur: scientists are working to bring dinosaurs back to life. They think they're getting close.(SCIENCE)(Cover story)." Maclean's 122.32 (August 24, 2009): 40(4). Academic OneFile. Gale. BROWARD COUNTY LIBRARY. 4 Oct. 2009
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