In my recently released trade book The Consuming Instinct: What Juicy Burgers, Ferraris, Pornography and Gift Giving Reveal About Human Nature, I discuss the evolutionary roots of gift giving. Specifically, I tackle gift giving rituals as carried out between family members (kin selection), between friends (reciprocal altruism), or between romantic partners (see here for one of my earlier posts on this topic).
In chapter 4 of The Consuming Instinct, I tackle wedding gifts and propose several hypotheses including that family members from the maternal side of both the bride and the groom should offer larger gifts than their paternal counterparts. This is based on the evolutionary principle that the extent to which we invest in kin is based not only on the degree of genetic relatedness (e.g., on average, we invest more in our siblings than in our second cousins) but also is shaped by the genetic certainty of the relationship. Paternity uncertainty exists. Maternity uncertainty does not. This is precisely why several studies (e.g., see here, here, and here) have documented the effect known as differential grandparental solicitude, namely maternal grandmothers and paternal grandfathers invest the most and least respectively in their grandchildren (even though all four grandparents possess the same degree of assumed genetic relatedness to their grandchildren).
I recently joined forces with three Israeli colleagues (Sigal Tifferet, Mali Meiri, and Nir Ido) to test this idea, using gift giving data from Israeli weddings. We'll hopefully be submitting the paper for publication in the near future. Until then, here are the two key findings: (1) the size of the monetary gifts is correlated with the genetic relatedness between the bride/groom and the gift offerers (e.g., siblings offer larger gifts than nephews). This is in line with the findings that Tripat Gill and I obtained in our 2003 gift giving paper (as covered in one of my earlier posts here). (2) Guests from the maternal side of both the bride and groom offer larger gifts than their paternal counterparts.
Bottom line: If you are about to wed, and you wish to maximize the size of the aggregate loot that you'll receive as gifts, tilt the guest list toward your maternal side of the family!