Chickens are evolving faster than previously thought, according to new research that challenges ideas of when they were domesticated and may have implications for human migration.

The findings, published in journal Biology Letters, are based on a genetic analysis of a chicken population that can be traced back over 50 generations.

The international team of researchers sequenced 12 mitochondrial genomes - DNA generally thought to be passed down from the mother to their offspring - in a well-known population of White Plymouth Rock chickens.

Two lineages of the White Plymouth Rock chicken - a small-sized chicken and a 10-times larger chicken - have been bred separately for 50 years.

The researchers found the rate of mutation since the two lineages split was up to 30 times the rate assumed for birds.

"Previously, the mutation rate in birds was generally thought to be about 1 per cent per million years.

In other words, DNA changes by 1 per cent every million years in birds," study co-author Associate Professor Simon Ho of Sydney University said.

"In our pedigree study, we estimated a rate of at least 4 per cent per million years, but perhaps up to 30 per cent per million years."

Pinpointing the rate of mutation is important for working out when chickens were domesticated.

"Our estimate [of when chickens were domesticated] depends on knowing the mutation rate of DNA," Dr Ho said.

"If we use an incorrect mutation rate, then our estimates of the timing of chicken domestication will be very wrong."

He said that this had been a problem in domestication studies of other animals such as dogs and cattle.

"In all of these cases, new mutation rates have shown us that domestication occurred much more recently than originally believed," Dr Ho said.

The researchers also found that in one case, mitochondrial DNA had been passed down from a father to its offspring.

"We've shown that it doesn't always pass from mother to offspring and it can mutate much more quickly than we thought." Dr Ho said.

Dr Ho said the study findings may change our understanding of bird evolution.

"The understanding of evolution is based on mitochondrial DNA," he said.

Chicken timing has implications for human migration

The research also has implications for our understanding of human migration, Dr Ho said.

"Chickens are one of the animals used as a proxy for human migration and especially colonising the Pacific, because humans carried chickens across the Pacific," he said.

Associate Professor Jeremy Austin of the Australian Centre for Ancient DNA at the University of Adelaide said the new molecular clock has the potential to "dramatically alter" the timing of when both chicken domestication and human migration events occurred in the Pacific.

He said the new data gives a better estimate of when things happened in the recent past.

"Having this new estimate means we are much more likely to get a more accurate picture of exactly when things like chicken domestication happened," said Dr Austin, who was not involved in the research.

Dr Austin and his team are currently studying mitochondrial DNA to understand the translocation of chickens into the Pacific.

"We may be able to apply this new rate to our data and see whether the dates for the original chickens in the islands and SE Asia and their movement out into the South Pacific correlates well with radiocarbon dating of human remains along that translocation route."

"We've always argued that chickens were more likely to be the animals transported first," Dr Austin said.

He said the new data would help his team test whether chickens were part of the initial migration or came later.

"That's important for understanding the whole archaeological history of the colonisation of the Pacific," Dr Austin said.

"Did humans carry living food items with them on those initial voyages or did they just go out blind and live off the land?"