Two Montreal researchers have proposed a new theory for a question that has long vexed evolutionary biologists: How did a mechanism thought to help build life self-assemble?

Sergey Steinberg, a biochemistry professor at the University of Montreal, found the answer in the ribosome, a relatively large mechanism within the cell that takes RNA instruction and builds proteins.

His discovery, made with student Konstantin Bokov, has been published in the scientific journal Nature.

Scientists have long wondered how chemicals spontaneously came together to create proteins before life itself began.

Steinberg and Bokov's theory fills in a critical step in how life got started four billion years ago, said Stephen Michnick, the Canada Research Chair in Integrative Genomics at the University of Montreal.

A key breakthrough came when Steinberg found that chemicals could spontaneously come together and form something as complex as a ribosome. Previous theories had suggested only simple proteins could form spontaneously.

This had been shown in a seminal experiment in the 1950s in which basic chemicals were combined in a flask, heated and zapped with electricity, creating basic amino acids as a result.

But proving that chemicals can spontaneously form simple amino acids did not prove that spontaneous action could create more complex mechanisms.

"In the absence of such explanations, some people could imagine unseen forces at work when such complex structures emerge in nature," said Steinberg.

Steinberg was able to show otherwise. He found the ribosome was put together using relatively simple structural rules, a bit like a three-dimensional puzzle. For critics who ask why spontaneous formation didn't lead to something other than the ribosome, Steinberg used mathematical models to show there was no other possibility. The ribosome simply wouldn't hold together if it were constructed any other way.

"The assembly followed rules that were logical and for which there were no alternatives," said Michnick. "This forces us to think about bigger structures. This type of thinking is important to understanding all sorts of structure."

For instance, the next step might be to consider why proteins begin to form wrongly spontaneously.

Several neurodegenerative diseases occur when proteins start to malform, said Michnick. Steinberg's research could give insight in how that happens, and why.