Understanding that Two Percent

By | November 11, 2008

Humans and chimpanzees are genetically almost identical — there’s only about a 2% difference between the DNA sequences of the two species. So what is in that 2% that makes us so different?

Exploring the Genetic Differences Between Chimps and Humans

A new comparison of chimpanzee and human genomes has offered an early but tantalizing look into what makes the two species, nearly identical at the DNA level, so different.

Scientists found key differences in areas linked to cell differentiation and immune response — and that could be just the beginning.

“By looking at all the variations, we will get a catalog, and when we find a variation in a person with a disease, it will help us understand the function of that variation,” said study co-author Richard Redon, a geneticist at the Wellcome Trust Sanger Institute. “It will help us understand better how our species emerged.”

Researchers already know that humans and chimpanzees share about 98 percent of the same genes. But rather than searching for mutations, Redon’s team looked at a relatively unstudied phenomenon known as copy number variation, or CNV, in which genes are redundantly duplicated.

These variations were ignored in the early days of genetics, but have recently been recognized as important: Mutations are more likely to accumulate in a given type of gene when multiple copies exist, and the simultaneous application of multiple genes can provide a functional boost.

Redon’s team is the first to assemble maps of CNV similarities across both chimpanzees and humans, and then compare the maps to each other. What roles those cell differentiation and immune response variants might play isn’t yet known — but the details of the findings, said Redon, are less important than the example set by the study, published today in Genome Research.

“It’s just a start,” he said. “We used a platform that isn’t very high-resolution. We found the largest variations, but the smaller ones, maybe we missed. And the biggest aren’t the most important — it’s just a matter of size. Some of the littlest changes can have the largest effect.”

It’s interesting that what appeared to be redundant, non-functional information may have an important role to play, serving as some kind of mutation incubator. But is the difference simply that we lucked out in the mutation department? Is the 2% genetic difference really the difference between us and chimps?

Or to put the question another way — how much of the difference between us and chimps is genetic, and how much is behavioral / cultural. Of course, there is a major connection between what’s in our genes and how we have structured human society and what’s in their genes and how they have structured chimp society. But I wonder if genes account for the total difference. I wonder if, under different circumstances, chimps might have been capable of mastering fire, or producing the Sistine Chapel.

Or maybe I’m looking at this thing all wrong. Maybe it’s the 2% genetics, maybe it’s the cultural / social structures we created, but whatever the contributing factors, maybe the simple truth is that we are the chimps who did those things. Or maybe they’re the humans who chose not to.

Either way, that’s probably closer to the truth than many of us are comfortable with.

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