Mythbusting: Are women’s hips too small for childbirth?
By Julia Jones
Have you heard of the phrase obstetric dilemma?
It's a bit of a fancy phrase, but it just refers to the theory that female hips are too small and babies' heads are too big.
This idea came about because human babies are born so vulnerable. They can't eat, walk, or communicate on their own and they require a lot of care from adults.
So the obstetric dilemma is a theory that explains this vulnerability by proposing that human female hips couldn't grow any bigger to accommodate their babies’ large head sizes. Therefore human babies are born prematurely, before they are really ready.
Scientists proposed that walking on two legs is more efficient for people with narrow hips, but giving birth to large-brained babies requires wide hips. The hypothesis is that female hip width is a compromise between bipedal efficiency and brain size at birth. Babies have to be born before their brains grew too big to fit through a pelvis.
This idea was proposed by a man in 1960 and has since influenced medicine, biology, and anatomy. You might not have heard of the phrase obstetric dilemma, but many people in our culture likely have this basic idea that women's hips are too small and babies have to come out before they're ready. It's one of those ideas that's permeated many different areas of knowledge.
But does that make it true?
Unpacking the obstetric dilemma
The obstetric dilemma was proposed as an explanation for the vulnerability of human babies. But the theory was never tested, it was simply accepted.
Does this idea hold any truth at all? What else might explain why our babies being born vulnerable?
Holly Dunsworth set about to explore this. She's an evolutionary anthropologist, and she's a mother herself. She's particularly interested in how anatomical, physiological, and behavioural traits relate to growing, producing, and raising offspring. She’s also interested in how our narratives impact other realms of knowledge and practice like parenting, healthcare and medicine.
So she was curious about this obstetric dilemma that was never proven, yet has influenced so many of our areas of knowledge.
In order to study this and figure out if it were true or not, Holly explored two questions.
Are humans different from other primates?
Firstly, she compared human and primate neonatal brain size and gestation length. Do our closest animal relatives have similar lengths of pregnancy? Are their babies born with similar-sized brains?
She found that it was not that different after all. Humans aren’t particularly unusual among primates in terms of brain size and gestation length. So it doesn’t appear babies are born ‘premature’ at all.
Do wider hips make walking inefficient?
Secondly, Dunsworth studied the mechanics and energetics of human movement to test the idea that wider hips were less efficient at bipedal movement. Unsurprisingly, in a world built for and by men, that idea came about because the male body is considered standard - the default human body. Therefore, any deviation from a male body, for example, having wider hips, was considered inferior.
People genuinely believed that wider hips meant women couldn't run as fast. They thought that women couldn't turn calories into movement as efficiently.
But Holly found that this belief just isn't true. If women needed to evolve to have bigger hips, this could have easily happened without it affecting their capacity to move around. So that's clearly not the reason human babies are born so vulnerable.
Our bodies are not broken
I emailed Holly Dunsworth about this. Here’s an extract from my conversation with her. She says:
“‘We absolutely have larger brains at birth compared to all other primates, and we have similar, or even long, not short gestation compared to all the rest too. So I say, and others do too, that we are not born early at all. We just have lots more brain growth to experience after we’re born than other primates. I definitely think it’s the journey that’s more important than the destination, so what goes into brain development and what goes on during it is the key factor in our evolutionary history, more than the resulting huge brain at the end of the process. Our bodies are not broken. There is no obstetrical dilemma.’ ”
If our hips are the right size and our babies are born at the right time, why, then, are human babies born so vulnerable?
If it's about the journey and not about the destination, what does that mean?
Imagine the experience of a baby inside a womb. It's dark, the temperature's regulated, and the sounds are muted. It's a very homogenous experience, with little variety.
Then, imagine that after the baby's born, adults are constantly holding the baby, stroking the baby, talking to the baby, looking into the baby's eyes, rocking them, and cuddling them. There's so much sensory stimulation and so much connection and love.
Maybe this is actually the key.
When we develop in a community of love and care, our brains are set up for lifetime of love and care. This early brain development contributes to our key strength as humans, complex societies filled with trust, empathy and compassion.
Early childbirth isn’t a flaw
What if early childbirth isn't actually a mistake at all? What if it is all part of our evolutionary design?
Vulnerable babies may be our greatest strength. They create the need for complex social relations and highly developed empathy. Without this rich network of social relationships, humans would have evolved very differently.
To learn more about how vulnerable babies impacted human evolution, read Are humans mothering in captivity?
