Grandmother hypothesis: lower mortality of the most X-chromosomally related grandchildren

[steven johnson]

It was discovered that the effect of a grandmother's presence on grandchild survivorship corresponds relatively with her X-relatedness to the grandchild, which is not equivalent in boys and girls.

A child mortality in the first three years of life it was found that a grandmothers' effect on grandchildren varies according to their X-chromosome relatedness.

Maternal grandmothers have 25% X relatedness with both grandsons and granddaughters and both grandchildren are equally likely to inherit any one of her X-linked genes but paternal grandmothers have no X relatedness with grandsons and a 25% relatedness with granddaughters. The influence of the grandmothers parallels the relatedness to the grandchildren.

Daryl Dawkins and his 'selfish gene' hypothesis has some support here.

While the Elephant Man may not have been an 'animal', apparently grandmothers are.

Contrastingly, paternal grandmothers will pass on one of her X chromosomes to their granddaughters (making them 50% X-related) but she will not pass this chromosome on to her grandson (making them 0% X-related).

"The presence of a paternal grandmother in all seven of the populations had a harmful effect on grandsons because her presence was linked with an increase in mortality.

"Meanwhile, in six out of seven populations, the paternal grandmother's presence in her granddaughter's early life had a beneficial effect in terms of the risk of mortality. This difference between paternal grandsons and granddaughters would explain a lot of the inconsistencies in previous studies, where the sex of the grandchild was not considered.

"We've only looked at child mortality, and the mechanism itself remains mysterious. Other studies have given evidence against conscious favouritism towards one grandchild or another".

The importance of grandmothers in the lives of their grandchildren

[pnwmom]

1. Do paternal g-mothers have 25% or 50% x-relatedness with g-daughters?

The OP says both. (I think the answer would be 50%.)

Interesting. I have often thought that my daughter was a happier version of my mother-in-law -- what my m.i.l. might have been like, if her environment had been different.

[Chemisse]

4. I am confused too - it seems like they would be 25 %

You give your daughter one of your X's and she gets the other from her father, making her 50 % x related to you. She then gives one to her daughter, and to her son, making the grandmother 25 % x-related to the maternal grandchildren.

You give your X to your son, so he is 50 % x-related. Then he gives that same X to his daughter, for a 25 % x-relatedness. But your X does not get included with his son, so you have no x-relationship with him.

[truedelphi]

2. I am confused as to what the term "Survivorship" means in this context.

The hour is late, but if someone's X chromosome-influenced grey matter can help them explain this to me, I will appreciate it in the AM.

[caraher]

3. You meant Richard Dawkins, right?

Though I'm endlessly amused by the notion of a big idea in genetics coming from the mind of Chocolate Thunder... no doubt discovered during his research back on the planet Lovetron. ;)

[Chemisse]

5. What I don't understand is

Why the XY chromosomes should be so important.

A grandmother may have 0 x-relatedness to her paternal grandson, but there are 22 other chromosomes in which she plays an equal part. Why would she not feel invested in the boy who shares 25 % of all her OTHER chromosomes?

[struggle4progress]

6. Do we actually have a title and a journal for a published paper?

This doesn't seem to be the sort of research Leslie Knapp usually does in Biological Anthropology at Cambridge:

My research interests center on the study of genetic variation in human and non-human primate populations. Specifically, I seek to understand how demography and environment influence genetic diversity and how genetic factors influence inter-individual differences in health, reproductive success and behavior in humans and other primates. My work also involves the application of molecular genetic data to questions of primate taxonomy and evolution. As a PhD student at UCLA, my doctoral research focused on the investigation of immunogenetic factors contributing to pregnancy wastage in pigtailed macaques (Macaca nemestrina). The basis for this research was the observation that immunogenetic similarity between mates is associated with decreased fecundability and increased fetal wastage in some mammalian species. Although controversial, studies in humans, rodents and swine suggested that the highly polymorphic genetic loci responsible for immune response and graft rejection (i.e., the major histocompatibility complex, or MHC) also played a role in reproductive outcome. My doctoral studies of histocompatibility antigen sharing among reproductively successful and unsuccessful pigtailed macaque couples revealed a highly significant amount of MHC antigen sharing among unsuccessful breeders. These findings provide compelling support for MHC, or MHC-linked, genes playing a critical role in primate reproduction. This research also suggests that prenatal selection may represent an additional mechanism for the maintenance of genetic diversity in the major histocompatibility complex and that there is a need for continued study of MHC genes and reproduction in primates ... http://www-prime.bioanth.cam.ac.uk/lak.html