PRODUCERS: Barrett Golding
We humans think we are pretty special creatures within the animal kingdom. But as scientists try to understand what makes us different from other animals, they keep running into what makes us the same.
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At the beginning of the millennium we hoped the human genome sequence would be the holy grail of the biological quest, answering questions on evolution, health, medicine, and what it means to be human. The current count though, is a little surprising: scientists have identified fewer than 25,000 genes in humans. That's more than a roundworm's 19,000, but far fewer than the 40,000 genes in corn. Clearly, genes alone can't explain the complexity, diversity, and development of life on Earth, so what do they mean?
Host John Hockenberry lives just a few miles from the Congo Gorilla Forest, part of the world-famous Bronx Zoo. What better place to contemplate the genetic similarities and differences between humans and other species? Nucleotide for nucleotide, human and chimp DNA, for example, are very much alike. So why (and how) do we look, think, and behave so differently? Where does our DNA diverge from and converge with other species? And why does it matter?
These are the questions we ask leading scientists around the country. We visit Ross Hardison, head of the Center for Comparative Genomics and Bioinformatics at Pennsylvania State University. His team lines up different genomes, such as rat, human, chicken, and chimp, to find out which genes are common, or "conserved," in all organisms, and which are unique only to specific species. Once lined up, scientists can begin to consider the function of genes, the genes that have most recently adapted, and the sections of DNA that show up in species separated from a common ancestor.
Are We Just Remodeled Apes?
Sean Carroll of the University of Wisconsin leads the field of Evo-Devo, combining evolutionary and developmental biology. He and fellow researchers discovered the revolutionary idea that nature uses similar genes to express similar traits. The fly eye, the human eye, and photosensitive bacteria all collect light using the same genetic "toolkit." In fact, based on the similarity of our genetic "recipes," says Carroll, human beings are really just "remodeled apes." "The more you look at the genetics, the less unique we are. We don't even have more genes than a puffer fish. So, you're just going to have to get over that"
So, then, what does set us apart? According to the high school students at the Bronx Zoo, it's our intelligence. "I mean, you look at humans, we're like this scrawny, hairless, little thing, and almost any animal can overpower us physically. Our only advantage is intelligence."
Intelligence? Is that actually true? And what is intelligence, anyway?
Daniel Povinelli, who heads the Cognitive Evolution Group at the University of Louisiana at Lafayette, has spent twenty years comparing the learning styles of chimps and humans. He doesn't believe that chimps have the capacity for abstract thought. But, he says, the question of intelligence isn't that simple. "The human mind is incredibly powerful. It wants to go out and reshape the world in its own image. But is that really what we want to hinge our understanding of chimps on is the way our minds work?"
William Fields, a researcher at the Great Ape Research Center in Des Moines, Iowa, is trying to understand the way chimps' minds work by studying how chimps acquire and learn human language.
"She learned just the way children learn language," he says of bonobo chimp, Panbanisha. "She acquired it just by being exposed to it, to humans using the lexigrams around her."
And what does a chimp say when she's given the power to speak? According to Panbanisha's use of computerized lexigrams, she immediately demands a decaf caramel macchiato.
So if both apes and humans have the capacity for language, why do we talk and chimps grunt? Erich Jarvis, who studies vocal communication at Duke University, says it's all about the inherent neurological pathways that give us particular motor skills—the ability to use our vocal chords to form words, for example.
Donald Kroodsma, former biology professor at University of Massachussetts at Amherst and author of the book The Singing Life of Birds, agrees. He, says that baby songbirds learn to sing like we learn to speak—by repeating and copying vocalizations from adult birds.
Even the theory of genetic mutation as the engine for evolution is now, itself, evolving. Lynn Margulis, of the Department of Geosciences at the University of Massachusetts, has pioneered research on "symbiosis," in which two organisms such as bacteria combine to form a new species, which blends the genetic information of the two. Once thought to be a rare event, her theory of symbiogenesis is now believed to be a major agent of evolutionary change.