Science of Love, Sex, and Babies

Where Do Demanding, Unweanable Babies Come From?

Posted in news, parenting, pregnancy, psychology, science by jenapincott on May 24, 2011

A season ago, when my daughter reached the six-month mark, her pediatrician told us to introduce her to a new food every few days and see what she likes. It wasn’t time to wean her, but soon it will be, and supplementation should help the transition. So I lovingly shopped for organic fruits and vegetables: apples, bananas, avocados, peas, and so on. I presented them passively — as items for her to experiment withon her placemat — and actively, by making mmmms, playing airplane, and swallowing the goop and showing her my tongue.

Three months later, we’ve made astonishingly little progress on the solids front. At best, the infant deigns to nibble delicately on peas and lentils. She’ll squish the bits of mango and avocado on her plate and drop them on the floor. She’ll taste a food then whip her head to the other side and bat away the spoon. She wrinkles her nose.

All she really wants to do is nurse. Baby loves to nurse. She cries and cries in the wee hours of the morning because she wants to nurse. She is tall and heavy for her age.

Who’s to blame (at least in part) for her unweanable stubbornness?

Her dad. 

It’s not only convenient to blame the father for babies who won’t give up nursing, It’s scientific.  There’s evidence.    

Here’s how it works, according to a new study Bernard Crespi, an evolutionary biologist at Simon Fraser University.  How much and how long a baby nurses depends in part on her genes. The genes she inherits from her father have an ulterior motive.  Paternal genes want the baby to extract as much as possible from the mother.

Paternal genes are thought to influence:

  • suckling strength  (so the baby extracts as much milk as she can)
  • tongue size (a larger tongue is a better suction pump)
  • crying  (for maternal attention and food)
  • appetite and speed of eating
  • duration of breastfeeding before weaning
  • night-time suckling (results in suppression of periods, which helps delay future pregnancies/siblings)

The genes that influence these behaviors are active only when they come from the dad. This is called genetic imprinting — when only the genes from one parent are expressed. Dad’s genes strongly affect the intensity of infant behavior.  Only a tiny percentage of human genes are imprinted. 

Dad’s genes are greedy for a good reason. From a biological perspective he has nothing to lose by making sure this particular offspring who carries his genes demands a lot of her mom — including suckling often, crying a lot, and taking a long time to wean. This behavior may be essential to a child’s survival in a setting in which resources are limited. “Weaning” genes have been shaped this way under evolutionary pressure in a premonogamous era.

Mom’s genes, meanwhile, are more moderate.  They want the child to survive but dial back the feed controls. They’d prefer for a baby to self-feed and start solids sooner. Mom’s genes push moderation to save resources (time and energy) for her other (or future) offspring. When paternal genes are disabled and maternal genes are active, babies have Prader-Willi syndrome, a condition that manifests as inability to latch and suckle effectively, complacency, and lack of crying or other solicitation for food.  These infants wean early because they never really nurse. They fail to thrive.

Demanding, unweanable infants come from dads. At a minimum, paternal genes play a real role in their aggressive eating, crying, and nursing behaviors.  

Now that they’re outed, perhaps guilty fathers should be the ones to work the night shift and scrape  food off the floor?

2 Responses

Subscribe to comments with RSS.

  1. Titfortat said, on May 31, 2011 at 5:40 am

    Lol, and just when I was starting to get over being the cause of everything.😉
    Interesting post.

  2. business review said, on May 31, 2011 at 9:40 am

    …CAMBRIDGE Mass. July 28 2009 — An analysis of rare genetic disorders in which children lack some genes from one parent suggests that maternal and paternal genes engage in a subtle tug-of-war well into childhood and possibly as late as the onset of puberty….This striking new variety of intra-family conflict described this week in the Proceedings of the National Academy of Sciences is the latest wrinkle in the two-decades-old theory known as genomic imprinting which holds that each parent contributes genes that seek to nudge his or her childrens development in a direction most favorable and least costly to that parent…. Compared to other primates human babies are weaned quite early yet take a very long time to reach full nutritional independence and sexual maturity says author David Haig George Putnam Professor of Organismic and Evolutionary Biology in Harvard Universitys Faculty of Arts and Sciences. Evidence from disorders of genomic imprinting suggests that maternal and paternal genes may skirmish over the pace of human development. …Previous research has offered evidence of a genetic struggle for supremacy only during fetal development In the womb some genes of paternal origin have been shown to promote increased demands on mothers leading to fetal overgrowth while genes of maternal origin tend to have the opposite effect.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: