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No. 1957:
DNA Tracking

Today, where did we come from? The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

We have this new kitten and we're deep into the bonding process. Cat and human seek one another out -- play, cling, dance. We have so little, and so much, in common. Her hazel eyes search us out and seek cat-meanings in us. We try to find traces of ourselves in her. 

I thought about her when I heard of a group of geneticists at the Howard Hughes Medical Institute. They have a new way of addressing the archetypical problem of anthropology: What was the evolutionary path by which we humans came into being?

They've studied the DNA of different mammals -- primates, ro-dents, cats, pigs, horses, cows, dogs. They've been able to determine what portion each of us has in common with an eighty-million-year old ancestor.  New York Times science writer Carl Zimmer likens their work to the study of medieval manuscripts. 

We have many copies of one ancient text. All are slightly different, and no original survives. What, for example, did a particular book of the Bible look like twenty-five hundred years ago? We can't be sure but, by tracing the succession of copies of copies, we can build an increasingly accurate picture of the original. We've done that with Aristotle and with Genesis alike. 

Now we apply similar techniques to our DNA. The mathematics may be more advanced, but the logic is similar. We now can tell what portion of our common ancestor's DNA has been lost in each species of mammal today. Humans and horses have lost the most -- rodents the least. That new kitten, with her earnest curiosity about everything -- her utterly human curiosity -- has evolved nearly as far from her eighty-million-year old mother as you and I have.

So these geneticists paint a picture of our progenitor's DNA. Will it tell us what manner of beast, what kind of Adam, begat us? They're quick to say they have no plan to do a Jurassic Park retro-evolution. Rather, by learning the original form, they hope to learn more about the evolutionary sequences that produced both you and your dog -- both me and my kitten.

You might wonder about that eighty-million-year age. After all, life itself is much older. However, it places us in the late Cretaceous Period. Dinosaurs then ruled Earth, but small rodent-like mammals were just starting to appear among them. The upcoming Cenozoic Era would belong to those mammals, just taking form. One of those small Cretaceous beasts would be our own Adam -- our parent, and parent of all our fine animal relatives. Dylan Thomas wrote well over fifty years before this new study. But he didn't need it to understand the soul-settling kinship it describes. He said,

... animals thick as thieves
On God's rough tumbling grounds
(Hail to His beasthood!).
Beasts who sleep good and thin, ...

O kingdom of neighbors finned
Felled and quilled, flash to my patch
Work ark and the moonshine
Drinking Noah of the bay,
With pelt, and scale, and fleece:

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

M. Blanchette, E. D. Green, W. Miller, and D. Haussler, Reconstructing Large Regions of an Ancestral Mammalian Genome in Silico, Genome Research, Vol. 14, 2004, pp. 2412-2423. 

C. Zimmer, When Bats and Humans Were One and the Same. New York Times, Science Times, Tuesday, December 07, 2004, pg. D3.

D. Thomas, The Collected Poems of Dylan Thomas. New York: New Directions, 1952/1953, Author's Prologue, pp. xv-xviii


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