(See a National Geographic magazine feature on Darwin's theories of evolution.)
Why did the pace of evolution increase so dramatically?
Writing in the January 29 issue of the journal Physical Review Letters, Deem's team says that HGT may have played a significant role in allowing early multicellular organisms to develop into the living things we know today.
"The simple organisms are like the building blocks, the Legos," Deem explained.
"Once you have enough Lego pieces, you can make a more interesting structure fairly easily. It may have taken three billion years to make the pieces, but once you have the pieces, then you can put them together in many different ways."
The modular structure of genes has made them ideally suited for HGT to transfer desirable traits between species, he added.
Not everyone agrees how prominent a part this gene-swapping process has played in the evolution of larger organisms like plants and animals.
But HGT is likely responsible for the rapid evolution of microscopic organisms, said Otto Berg, a professor of molecular evolution at Sweden's Uppsala University who was not affiliated with the study.
"The conclusion that recombination [of genes] and HGT can speed up evolution, at least for microbes, will probably not be contested," Berg said.
HGT may become more prominent when species are put under heavy survival pressures, he added.
For example, when bacteria are exposed to antibiotics, they must become resistant or die. Any traits that bestow resistance to the drugs may therefore become widely transferred among species.
"When a population meets a new environmental challenge or a new ecological niche to exploit, [genetic] selection for new functions can be very strong, and HGT can play a crucial role," Berg said.
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