This might be explained by dietary habits depending on paternal resource.
Conflict between paternal and maternal resources during pregnancy is thought, at least in some cases, to drive imprinting of genes [13].
Parental genes may therefore be involved in a "tug-of-war" over maternal resources, with paternal genes promoting and maternal genes constraining fetal growth (Haig and Westoby, 1989; Moore and Haig, 1991).
The parental conflict hypothesis postulates that genomic imprinting in mammals evolved because of conflicting maternal and paternal interests in the allocation of maternal resources to the offspring with paternally epressed genes enhancing and maternally epressed genes limiting feto-placental growth.
Conflict happens with genes too: paternal genes help construct the placenta, an invasive organ designed to gain access to maternal resources, while maternal genes show greater involvement with the embryo itself.
Imprinting is thought to have evolved from a conflict between maternal and paternal genomes for the allocation of maternal resources.
This is in particular the case when female preferences are targeted at male characters that signal a high genetic quality (good genes sexual selection) or the ability to supply resources like paternal care (direct benefits sexual selection).
In humans, paternal care usually involves obtaining adequate resources to support children, which may require engaging in male male competition and maintaining high T levels.
If men had uteruses, "paternity wards" would get resources, ambulances would transport pregnant men to hospitals free of charge, deliveries would be free, and the Group of 8 industrialized nations would make paternal mortality a top priority.
Their version of the box includes breast pads to encourage breastfeeding, a brain-developing children's book by a Canadian author and a "Crib-Side Assistance" resource for fathers to encourage paternal bonding.
