A study involving over two million families of different cultural extraction, in 14 countries says that couples that live with the mother of the husband but particularly of the wife have fewer children respect to when grandma does not live at home. The opposite would have seemed more likely for a number of reasons. An extra hand that settles many of the things that otherwise mum and dad would have to look after might be an incentive to have more kids. The researchers’ view is different: the variable that most affects how many children a couple has is the probability that those children will survive their parents. There is an inverse relationship between the poverty of the nation where one is born (a parameter that is closely related to infant mortality) and number of children per family. The presence of grandma increases the chances that kids will be fed, looked after etc. This, increases their chances of reaching an age when they too will have kids. Thus, parents are reassured by the presence of grandma and therefore have less kids. The fact that this is so particularly when mother’s side grandma lives in the house would be because dad’s side grandma guarantees less assistance in the house since she is less certain that grandchildren are actually hers with respect to mum’s side grandma. Parents in turn have slightly more children although always less than when there is no grandma in the house.