Human birth is considered particularly complicated. Because we walk upright, we have a narrow pelvis and the large brain ensures that the baby’s head is particularly large. But apparently difficult births are by no means a uniquely human phenomenon. An analysis now shows that numerous other mammals struggle with similar problems – and have similarly high rates of complications and death during birth, both in captivity and in the wild.
For human women, it often takes well over twelve hours from the start of labor until the baby is finally born. The complication rate during childbirth is also high: although more and more women have access to professional medical care, according to the World Health Organization (WHO), around 786 women worldwide still died giving birth to their child every day in 2020.
The so-called birth dilemma is often cited as an explanation for why human birth is supposedly particularly difficult. According to this, the human pelvis has become increasingly narrow over the course of evolution due to the upright walk, while at the same time the child’s head grew due to the increasing size of the brain. This disproportion makes it difficult for the baby to pass through the birth canal. Animals, on the other hand, seem to have it easier: whether foals, piglets or calves, the offspring are usually out within a few hours.
Comparison with animals in captivity and in the wild
But is it really true that animals have fewer birth complications than humans? To test this, evolutionary biologist Nicole Gunstra from the University of Vienna evaluated numerous studies on birth difficulties in many different mammals, including domestic and farm animals such as cows, horses, pigs, dogs and cats, as well as wild animals in human care or in the wild, including deer, elephants, monkeys, seals and whales.
The result: “The analysis of the data collected shows that human birth is not really exceptional in terms of its risk,” reports Gunstra. The rates of birth complications and maternal mortality in many mammals were in a similar or even higher range than in humans – compared to data from indigenous peoples without modern medical care, including the Agta of the Philippines, the Hiwi of Venezuela and the Hadza of Tanzania, where up to 15 percent of women die in childbirth.
Evolutionary conflict of goals
Many animals also have one of the most common causes of birth problems, a mismatch between the size of the embryo and the diameter of the mother’s pelvis, in common with us humans. “This problem is particularly common in species with large, precocious offspring,” explains Gunstra. For example, the young animals of elephants, deer and horses can stand and run with the herd shortly after their birth – a decisive survival advantage, but at the expense of an unproblematic birth process.
According to Gunstra, it is precisely this evolutionary trade-off between easy birth of smaller young animals and improved survival chances for large newborns that probably ensures that natural selection has not led to a minimization of birth difficulties. Even with whales and manatees, which do not even have a fully ossified pelvis, it can happen that young animals that are too large get stuck in the birth canal. In species such as dogs and pigs, which usually give birth to litters of several young animals, there is also a further compromise in terms of litter size, because litters that are both too large and too small increase the risk of complications.
“These findings situate human birth difficulties within a broader mammalian pattern, rather than viewing them as a uniquely human phenomenon that requires extraordinary explanations,” Gunstra says. “Putting human birth into this broader context challenges entrenched assumptions and highlights the value of a comparative evolutionary perspective.”
Source: Nicole Gunstra (University of Vienna), Biological Reviews, doi: 10.1002/brv.70174