The National Human Genome Research Institute and several universities came to this conclusion after comparing the same stretch of DNA in 12 animals, including a pig and a dog, with human DNA.

"It provides some pretty definitive evidence that we are indeed closer to rodents than we are to carnivores," Dr Eric Green, scientific director of the NHGRI said on Wednesday.

Rodent relatives

"Our data really puts the nail in the case. In the (genetic) sequence you can find changes in the genome that clearly occurred in both humans and rodents but did not occur in others."  

The survey also backs up the argument that so-called junk DNA is nothing of the sort - it must do something important because it stays virtually identical across many species.

It also supports the theory that genes are only a small part of the genetic story.

DNA is very difficult to interpret - its long code is built on compounds known by the abbreviations A,C,T and G. 

DNA labyrinth

Reading the long string of four letters repeating in various combinations is proving to be even trickier than scientists thought it would be.

"In the (genetic) sequence you can find changes in the genome that clearly occurred in both humans and rodents but did not occur in others"

--Dr Eric Green, scientific director of the NHGRI   

At first they believed the genes - the sequences that control production of the body's protein building blocks - would be the only functioning parts of the sequence.

But it turns out there are sequences which control the genes, and perhaps which do even more.

"It now seems that about five percent of our genomes are functionally important," Green said.

Discoveries

"Only a third of that code is for genes. That means that two-thirds of what is functionally important is not (gene) encoding DNA. We don't even know what it looks like so how are we going to find it?"

Green hopes to do so by comparing the genomes of different species.

"This is the idea that you can truly use sequences from multiple genomes and analyze them all at once to try and find the small percent that is shared among all of them," he said.

"We believe this is going to be a very valuable way to find those sequences that are very important. 

"We will discover new types of functional elements in the coding DNA that we didn't even know existed," Green added.