Pet lovers sold a pup on old theory

A WELL-known “rule of paw” holds that you can tell how old your pooch is in human terms by multiplying its age in years by seven.

But in fact the real ratio changes over time, according to the US National Institutes of Health.

Scientists have identified chemical marks on the DNA that correspond to different developmental stages, an area of study called epigenetics.

The field is well established for humans, and some companies let you send in a DNA sample to determine your biological age by reading your “epigenetic clock”.

Molecules called methyl groups attach themselves to a particular region of the DNA, switching them to the “off” position and ushering in the next stage of life.

Based on a new formula devised for labradors, an eightweek-old pup is about equal to a nine-month-old human baby. Further investigation could include other breeds in a bid to understand the ageing process.