Scientists led by researchers at the National University of Ireland in Maynooth have solved the mystery of how complex life formed.

“Nature’s big bang” - when two single cells fused into one living organism - has been mapped for the first time by researchers.

Senior biologist Dr James McInerney said the discovery in effect traced humans’ oldest ancestors.

“This was a remarkable event, which appears to have happened only once,” he said. “These two primitive single cell life forms came together in an event that essentially allowed nature to grow big.”

Dr McInerney said the research would help explain what gave rise to all multi-cell organisms we know today - insects, plants, animals and humans.

Using genetics and information from the mapping of the yeast genome, evidence of two originally single cells, known as prokaryotes, were discovered in a eukaryote which formed with a nucleus.

Researchers were able to show that yeast - a model system for molecular biology - contained one eukaryote genome which came from two distinct different prokaryote genomes.

“It is in the nucleus that we find the DNA of all species, and for years it had been a puzzle as to how the first nucleus was created. Now we know," Dr McInerney said.

Researchers believe this can be dated to about two billion years after the oldest micro-fossils.

The discovery follows the mapping of the family tree of all nature by researchers at NUI Maynooth.

“Essentially, you had an organism, like the Minotaur in ancient Greece, and this, in biological terms is what we hypothesised was the common ancestor of all eukaryotic life," Dr McInerney said. “Because humans are eukaryotes, we were, in essence, trying to trace the deepest human ancestor.”

Dr McInerney, of NUI Maynooth’s Bioinformatics and Molecular Evolution Unit of the Department of Biology, collaborated with Dr James Cotton at the world-famous Sanger Institute in Cambridge, England, to make the discovery.

Their work has been published in the eminent Proceedings of the National Academy of Sciences, USA.

The discovery was made after 10 years research at NUI Maynooth and followed the sequencing of the yeast genome in 1997.