For animals that are fertilised internally, this is always a risk. It is a risk to humans throughout the world. A study in the UK of what is called ‘paternal discrepancy’ found that around 1 in 25 fathers in Britain may not actually be the biological parent of the child they believe to be theirs. In genealogy this is called a ‘non-paternity event’. As the old saying (some say originating in the Deep South of the United States) has it: ‘It is mother’s baby and father’s maybe.’
This is not justifiable. He is referring to a Liverpool John Moores University study based on contested paternity testing. It drew only from contested situations, making it not valid to make population-wide estimates from.
