Today, our last universal common ancestor. 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.

You may've noticed that I pick my stories from history. I usually leave current science and technology to reporters, since their material doesn't have to rerun at a later date. Current ideas in science and technology are always in a state of flux.

Take the matter of our Last Universal Common Ancestor, called LUCA for short. As we've gained the ability to trace our evolution backward, using DNA, many important things have come to light. We've learned, for example, how little humans and chimpanzees differ genetically. We've determined that humans, horses, and cats, have diverged more than rodents have, from the common ancestor of us all. 

But the tantalizing question is, who was that common ancestor -- an ape, a primitive horse, a fish? All of them had other forebears. We know that many, fairly-advanced beings were not in our own direct ancestral tree -- the Neanderthals, for example, or for that matter, even the monkeys. 

So science writer Garry Hamilton looks at attempts to determine how far back to we must go to find the common ancestor of all life on earth. Many primitive organisms existed, but which was our historical Adam? 

That question has dogged us since Darwin. Darwin himself wasn't sure whether all living creatures shared a single tree. But the complexity of DNA suggests that all living creatures have at least been kin since DNA came into being. DNA secures the kinship among animals, fungi, plants, and algae. So people who ask the LUCA question are looking back much further than any of these. 

For a while, evidence suggested that our LUCA ancestor was a bacterium. But here a problem arises because of the speed with which bacteria evolve. After all, we can watch them evolve in the laboratory. That distorts our attempts to trace them backward in time. 

So the emphasis shifts to determining the genetic structure of the minimal organism that could have evolved. Perhaps there never was just one LUCA -- but, instead, a general stew of organisms out of which several sets of organisms came. 

The question spins on today, in 2005. If we should rerun this program in three, or ten, years, things will already have shifted. Answers to questions about our origins (planetary or biological) are adding up at a furious rate.

As they do, anti-evolutionists evolve new arguments. Few still claim a 9000-year-old Adam. But now the term Intelligent Design, first coined by scientists, becomes a rallying cry against letting science reveal what it will. Naturally such unresolved questions as LUCA poses are aggravating if we dislike having to see through a glass darkly. That's a pity; for, if answers lead to new questions, we need to remember that questions also lead to new answers. And those answers increasingly display a complex, tantalizing universe that grows more awesome with each new revelation.

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

G. Hamilton, Mother Superior. New Scientist, Sept. 3-9, 2005, pp. 26-29 and Cover.

See also, Patrick Forterre's article.

My thanks to Carol Lienhard for suggesting the topic and to Richard Willson, UH Chemical Engineering, for his counsel.

Cookie with a DNA imprint, made for a reception in honor of James Watson, co-Nobel Prize winner for the discovery of DNA