A type of shark often used for fish and chips has been found to have the same DNA memory tags as those in the human body.
University of Otago geneticists have been looking into the DNA of the elephant shark, which is only found in New Zealand and Australian waters.
Research leader Tim Hore said the DNA memory system found in humans was made up of small tags known as methylation, which were used to direct cells to do specific jobs.
"Basically this is a mark that sits on top of DNA and it helps tell cells whether or not they should have certain genes expressed or not.
"So if we look at the liver for example, it only expresses liver genes mostly and not neurogenes," he said.
"So we know fairly well what this is doing in humans and how it exists in mammals but we don't really know where it came from."
Dr Hore said the gene system had only been found in vertebrates and researchers had long wondered how it evolved.
"We know, for example, that in insects they don't have this same type of DNA methylation, this tagging that sits on top of the genome."
The elephant shark was the oldest living vertebrate that Dr Hore and his team could find that had the methylation tags.
"We looked back through evolutionary time to try and see what was the oldest example that we could come across of this memory sitting there on the DNA and it turns out that it's the elephant shark," Dr Hore said.
By identifying the DNA in sharks it proved it was far more ancient than previously thought, he said.
The study would now be reviewed by international scientists.