(From the German Press Association Desk...)

German scientists claim mothers-in-law are such a menace that the presence of a father's mother in a family might increase the chance of a child dying.

Eckart Voland and Jan Beise based their findings on a survey of church records in the 18th and 19th centuries.

The report, in the New Scientist magazine, speculates that harassment of the mother by a father's mother might have had a negative effect on the child.

But the presence of the mother's mother could help the child in certain circumstances.

The researchers think that the negative effect could arise from doubts in the father's mother's mind that the baby really was her son's and that this led her to be less helpful than she otherwise might have been.
The research applied to rural peasant communities.

The two researchers think the old "evil mother-in-law" syndrome was a cultural phenomenon in strict religious societies.

A-HA! :D

It's all clearer now.