"These are the potential roots for the emergence of novel protein-protein interactions, which are the hallmark of evolution in complex, multicellular species," Lynch said. "In other words, the origins of some key aspects of the evolution of complexity may have their origins in completely nonadaptive processes."
Fernandez said the research reveals how increasingly specialized proteins can evolve. He drew an analogy to a business that hires two delivery drivers that initially cover the same parts of town but eventually specialize to deliver only to specific neighborhoods.
"Eventually, even if times become tough, you cannot lay off either of them because they each became so specialized that your company needs them both," he said.
The more simple a creature is, the fewer specialized proteins it possesses. Humans and other higher-order mammals need many specialized proteins to build the specialized tissues in their skin, skeleton and organs. Even more specialized proteins are needed to maintain and regulate them. This complexity requires that the duplicates of the original jack-of-all-trades gene be retained, but this does not happen unless selection is inefficient. This is frequently a point of contention between proponents of evolution and intelligent design.
Fernandez and Chen looked at duplicate genes across the human genome and found that the more poorly packed a protein was, the more likely it was to be distinguished through paralog specialization.
"This supports the case for evolution because it shows that you can drive complexity with random mutations in duplicate genes," Fernandez said. "But this also implies that random drift must prevail over Darwinian selection. In other words, if Darwinian selection were ruthlessly efficient in humans -- as it is in bacteria and unicellular eukaryotes -- then our level of complexity would not be possible."
|Contact: Jade Boyd|