"This is evolution in action."

Colin Simpfendorfer, a partner in Morgan's research from James Cook University, said initial studies suggested the hybrid species was relatively robust, with a number of generations discovered across 57 specimens.

The find was made during cataloguing work off Australia's east coast when Morgan said genetic testing showed certain sharks to be one species when physically they looked to be another.

The Australian black-tip is slightly smaller than its common cousin and can only live in tropical waters, but its hybrid offspring have been found 2,000 kilometres down the coast, in cooler seas.

It means the Australian black-tip could be adapting to ensure its survival as sea temperatures change because of global warming.

"If it hybridises with the common species it can effectively shift its range further south into cooler waters, so the effect of this hybridising is a range expansion," Morgan said.

"It's enabled a species restricted to the tropics to move into temperate waters."

Climate change and human fishing are some of the potential triggers being investigated by the team, with further genetic mapping also planned to examine whether it was an ancient process just discovered or a more recent phenomenon.

If the hybrid was found to be stronger than its parent species -- a literal survival of the fittest -- Simpfendorfer said it may eventually outlast its so-called pure-bred predecessors.

"We don't know whether that's the case here, but certainly we know that they are viable, they reproduce and that there are multiple generations of hybrids now that we can see from the genetic roadmap that we've generated from these animals," he said.

"Certainly it appears that they are fairly fit individuals."

The hybrids were extraorindarily abundant, accounting for up to 20 percent of black-tip populations in some areas, but Morgan said that didn't appear to be at the expense of their single-breed parents, adding to the mystery.

Simpfendorfer said the study, published late last month in Conservation Genetics, could challenge traditional ideas of how sharks had and were continuing to evolve.

"We thought we understood how species of sharks have separated, but what this is telling us is that in reality we probably don't fully understand the mechanisms that keep species of shark separate," he said.

"And in fact, this may be happening in more species than these two."