Fitness benefits of prolonged post-reproductive lifespan in women, MIRKKA LAHDENPERÄ et al., Nature 428, 178–181

The human is unusual among animals in that females often live for many years after ceasing reproduction. For this to be favoured during evolution, mothers that live long after ceasing reproduction should have more grandchildren, and hence propagate more genes, than those that live for only a short time. A proper test of this theory requires reproductive histories going back for several generations, and two sources have been found that fit the bill. Population registers taken by the Lutheran Church in Finland between 1702 and 1823, and in Quebec during the second half of the nineteenth century both show that a prolonged post-reproductive lifespan is associated with larger numbers of grandchildren. In the presence of a post-reproduction mother, offspring bred at a younger age and had children more frequently, and
their children had a better chance of surviving to adulthood.

Another bit from inside the article to show the older MC women when they are expected to finally die:
...mortality rates accelerate from the time that offspring begin to terminate reproduction suggest(ing) that selection for post-reproductive longevity is deferred only until a woman's own offspring finish reproducing.

I found it both amusing and interesting. But I have at least two questions to the authors:

(1) Could it not be vice versa, namely that many grandchildren are the reason for keeping old women longer fit?
(2) What is the use of Grandads then? Why have they not studied them too? Men can be caring and supportive as well as women.

(Now, SOPHIE, get out and stop crying, go to your mum, Daddy's at work, or so)

Wolfgang