I have been reading about evolutionary developmental biology. It’s hardly my proper purview, but when a dude who worked on Jurassic Park says a real-life resurrection may be in store for the dinosaur…well, please, tell me more.
I recently tried this stuff out at a dinner party and it didn’t disappoint, so I thought you guys might like to be in on it, if you weren’t already.
Evolutionary developmental biology, or evo-devo, is the subject of archeologist Jack Horner’s 2009 book, How To Build A Dinosaur, co-authored by New York Times science editor James Gorman.
Horner is not simply a movie consultant (though the character of Alan Grant in the Jurassic Park film is based on him). He’s a world-renowned paleontologist who discovered the first dinosaur eggs in the Western Hemisphere and developed the foundation of everything we know about dinosaur nesting, parenting, and even fossilized dino embryos.
As How To Build a Dinosaur unfolds, evo-devo does not seem to me like a new field of science, but rather a glorious, unheralded mash-up of paleontology, embryology, microbiology, genetics and evolutionary science. There’s something for everyone, except, of course, the Creationists. To them, a chicken is a chicken because the Bible says so – rest assured: there was a coop aboard Noah’s Ark.
Contemporary evo-devo devotees want to know how different creatures’ development itself evolved. What can we learn about relationships between different species by looking at similarities in their embryonic development? Can we track the evolution of their developmental processes? To scientists and thinkers like Horner and Gorman, the humble chicken, just like you and me, is a punctuation mark on the whole stunning spectrum of life on Earth. Instead of seizing upon the profound personal insignificance this perspective could excite, I would rather dwell on the amazing reality of my connection to everything else that ever lived on the planet.
Of course, most of the things that swam, walked, hopped, crawled, ran, photosynthesized and flew on the face of the earth are extinct. Six billion years or so is a long time. If Earth’s history was a 24-hour TV schedule, humans probably wouldn’t even fill up the time-slot of a Geico commercial.
Anyway, part of the reason we’re all so well-connected – whether living or extinct – is that nature is more economical than my Aunt Doreen, who refused to throw out yogurt cups in case someone could use them. Just as Aunt Dor knew that the yogurt cups could become bead-holders or kindergarteners’ projects, nature knows that the genes of different species need only be modified, not replaced (you, my friend, share almost 60% of your genes with the fruit flies in your kitchen).
Evo-devo helps us to understand that when new species of animal emerge, nature hasn’t formed their genes from scratch. Instead, their genes are sculpted and modified from existing genetic codes. In many cases, vast physical differences between earlier and later species who share a common ancestor are less a matter of different genes and more a matter of similar genes being expressed (switched “on” or “off”) in different ways. If you go far enough back on the evolutionary tree, you’ll find some pretty surprising common ancestors. For example, it is generally accepted nowadays that if you want to glimpse dinosaurs’ living relatives, don’t look for geckos and alligators. Hang a birdfeeder.
Based on what they can deduce about the bone structure and anatomy of dinosaurs, paleontologists have been suggesting for years that modern birds are descended from dinosaurs. As Horner points out, there is even a distinctive kind of bone tissue found nowhere in the world but in female birds just prior to egg-laying. Now, we’ve also found it in the fossilized bones of a female T-Rex.
As Horner explains at length, the field of paleontology, traditionally a realm of fossil-hunters and educated guesses based on the assembly of fossilized skeletons and maybe a few eggs and footprints, is merging with radical new technologies that allow us to look into the microscopic physical and chemical structure of dinosaur bones like we never have before. As new technologies allow us to extract proteins and collagens and even the traces of blood cells and vessels from fossilized remains (though not DNA, not yet) and compare them to the make-up of living creatures, it becomes more and more clear that birds and dinosaurs are not-so-distant cousins.
Here, I would just like to say that it’s about time someone pulverized a dinosaur bone and put it into a mass spectrometer. Thank you for bringing this to my attention, Mr. Horner.
Embryology joins the fray as well. The history of the relationship of embryology and evolutionary science is complicated – a formerly popular, overly-simplified theory states that developing embryos can be seen to briefly exhibit characteristics of all the species that preceded them. This view has fallen in and out of favor, and while it’s far from an exact science at this point, it’s at least been invited back to the party along with modern paleontology, microbiology, genetic and evolutionary sciences. I’ll tell you more in a minute.
As Horner explains, the idea of bringing dinosaurs back to life with preserved DNA à la Michael Crichton’s Jurassic Park will always be fiction. As far as we can tell, there just isn’t any actual DNA to be found in bodies that are over 65 million years old.
Unless you know where to look – and you have a modicum of genetic science at your disposal.
How about the genes of a living animal which calls the dinosaurs family?
Here is where embryology looms large in the research Horner profiles. Did you know that while no modern bird’s skeleton includes a true tail, a chicken embryo (given to exhaustive investigation due to its size and easy availability) briefly and confidently exhibits the beginnings of eighteen extra vertebrae – a very long tail for an embryo the size of a quarter. Then, in a process that shocked observing scientists, the growth process of this tail comes to a complete halt and then reverses itself into the modern single nub of bone that modern birds sport at the end of their backbones (this is a drastically over-simplified version, read the book for yourself, ok?).
Just as paleontologists puzzle over exactly when certain anatomical changes occur in the great sweep of evolution, with slowly morphing fossil forms as their evidence, modern lab scientists hang giddily over chicken eggs to figure out exactly what gene factors regulate both the growth and the disappearance of their chickies’ tails. Are these the same genes whose modification over time led to the loss of a tail in birds, whose species owe their lineage to the dinosaurs?
In other words, the genes for dinosaur tails may be running all over the henhouse – they’ve just been switched off.
Can we figure out which factors are responsible for halting that tail growth in modern bird embryos? If so, could we turn those factors off and hatch a chicken with a great big tail? Or teeth? Or arms instead of wings? It’s possible.
There are massive challenges – like proving the chicken-with-a-tail has in fact harkened back to a natural earlier genetic form, rather than being a one-time modern freak. Plus there’s the problem that no-one’s really studied the development of tails like they’ve studied the development of, for example, limbs (it seems that people are chiefly interested in the structures they possess). What would we compare the results of our dino-tail experiments to, if we’re not even sure of the basic laws of normal tail genetics? Scientists are working on it.
Those who would throw up their hands and wish that science could devote itself to something more useful than vestigial dino tails should remember that tails are extensions of the backbone and spinal cord, and therefore the study of tail growth could unlock new knowledge of spinal growth factors in all vertebrates, including, for example, babies born with Spina bifida. Knowing what gene factors contribute to proper spinal growth could open a whole new world of prevention for life-threatening birth defects. Thanks, dino-chickens.
It all comes back to the same idea, you see. We’re all connected.
And now, I have little more to add but two pieces of my own scientifically-based artwork, which are sure to have invaluable benefit to scientists working in every aspect of this field.
P.S. If you’re interested in reading more about evolutionary science at work in American culture, particularly if you are religious, I highly recommend Monkey Girl by Edward Humes and Finding Darwin’s God by Kenneth Miller.