From time to time, I think we all need reassurance that we matter. That our seat at the game has not been taken by someone else. Could not be taken… Maybe that’s why we’re given names -so there’s no mistake. And if we’re not there all the time, it’s only because we sometimes have other duties to perform.
In many species, the male role in procreation can seem like that, I suppose: a postal service that’s only charged with delivering letters, not reading them, not dealing with the contents. At least that’s how it looks from across the street. On closer inspection, though, it would seem that the delivered mail is far more complex than it first appeared. It’s almost as if whoever reads the letter not only sees the blueprint, and the construction manual, but much like reading a newspaper, also learns of other important things which, at first glance seemed unrelated, but in the end, profoundly affect the building.
These processes would obviously be difficult to study in humans, so often we have to model them in other species and extrapolate the results to our own kind. Two articles in the Smithsonian magazine outline some of this information.
There are at least two time frames when the male influence on the resulting offspring was unsuspected: before conception -in fact, even before meeting his potential mate- and during growth and development of the fetus, and even its neonatal care. The how is interesting, but equally so is the why, I think.
First, let’s consider the production of sperm in isolation from its immediate need. https://www.smithsonianmag.com/science-nature/dads-pass-more-genetics-their-sperm-180969760
Sperm are produced in the testes, and then travel to a storage area via the epididymis -a long, wriggly 6 meter long tube in the human. It’s in the epididymis that the sperm mature and become motile. ‘As sperm traverse the male reproductive system, they jettison and acquire non-genetic cargo that fundamentally alters sperm before ejaculation. These modifications not only communicate the father’s current state of wellbeing, but can also have drastic consequences on the viability of future offspring.’ Sperm contain genes, of course, but simply having the instructions doesn’t mean they will be carried out. Genes can be turned on, off, or down, by other mechanisms –epigenetics. ‘One of the most powerful members of the epigenetic toolkit is a class of molecules called small RNAs. Small RNAs can conceal genetic information from the cellular machinery that carries out their instructions, effectively ghosting genes out of existence.’ The father’s previous diet, stress levels, and so forth can all have an effect on these small RNAs, and the small RNAs are in turn shed or reacquired as the sperm continue their journeys along the epididymis.
And then, as I mentioned, there is an effect on the developing embryo whether or not the male is actively involved with the female during her gestation or in the subsequent rearing of their offspring. https://www.smithsonianmag.com/science-nature/how-dads-genes-can-prepare-mom-parenthood-180969793 Although the data is from mice, it turns out that ‘The paternal genes a fetus carries can impact the maternal brain during pregnancy, priming her to allocate more or less of her time to tending to her kids.’
‘A child that procures as many nutrients as possible from mom can secure a father’s lineage at no cost to him—but a mother still needs to prioritize her own wellbeing during pregnancy and early childcare.
‘This sexual conflict is well exemplified by a gene called Igf2, which drives the rapid growth of fetal cells. Like most of our genetic material, Igf2 is inherited in pairs—one copy from mom and one copy from dad. But in contrast to other genes, only the version from dad gets put to work. The Igf2 from mom, on the other hand, is stifled through a chemical modification that acts like a muffler on an engine. Mom’s Igf2 DNA undergoes no changes—but the gene’s instructions can no longer be heard over the din of the cellular milieu. […] If an error occurs that also switches on the mother’s copy of Igf2, the baby quickly balloons in size. This could be good news for dad—a big baby is more likely to survive—but mom can get in serious trouble if she has to carry and birth an unmanageably large fetus.
‘To guard against this possibility, females have developed their own failsafe: another gene called Igf2r. The “r” stands for “receptor”: the product of this gene can sop up free-floating IGF-2 proteins before they exert their growth-promoting effects. Unsurprisingly, dad’s copy of Igf2r stays quiet. Such is the phenomenon of genomic imprinting—a form of non-genetic inheritance in which both copies of a gene exist, but only one parent’s version is left intact. Over 150 imprinted genes have been confirmed in mice, about half of which have conserved counterparts in humans.’
Suffice it to say that there are several other paternal genes that code for growth or neonatal behaviours that can affect the mother’s response and subsequent care of her offspring -a kind of effect that evolution has decided would be in the best interests of all concerned.
For example, ‘expression of an imprinted gene called Phlda2 in a fetus hinders the growth of hormone-secreting placental cells. These hormones recruit nutrients to support early development. Unsurprisingly, the offspring’s paternal copy of Phlda2 is kept under wraps. But mothers want their copy to remain switched on. […] Other researchers had noted that these hormones weren’t just working in the placenta, however. Throughout pregnancy, they were actually spreading throughout the mother’s body and accumulating in her brain—leading John [professor of biology at Cardiff University] to suspect that they could also be encouraging a mother to care for her young. […] The team’s work lends credence to the idea that fathers don’t dictate the health of children through genetic inheritance alone. In cases like these, they can even utilize the fetus as a chemical envoy in this battle between male and female, swaying a mother’s priorities towards more attentive childcare.’
During many of the years when I was in active practice of obstetrics, I often felt I needed to be an apologist for the father who did not have to suffer the many exigencies of pregnancy, not to mention the difficulties of labour and delivery. Clearly, after fertilization, his role in the process seemed merely supportive, and often peripheral.
Were I to start my career over again, though, perhaps I could put in a louder word for the importance of our male side -although I’m not at all sure mom would be listening as intently at the end.