Study Reveals Childbirth Challenges Are Widespread Among Mammals

Childbirth difficulties are not confined to humans, according to a recent comprehensive study examining a wide range of mammalian species. The research indicates that challenging deliveries, including those resulting in maternal mortality, occur frequently in both wild and domestic mammals, rivaling rates seen in human populations lacking modern medical care.

Scientists have traditionally attributed the complexity of human birth to the “obstetrical dilemma,” which posits that evolutionary pressures for upright walking and large brain size have created a narrow birth canal, complicating delivery. However, this new study questions the uniqueness of this dilemma by analyzing childbirth complications across various mammals.

Comparative Analysis of Birth Complications

Nicole Grunstra from the University of Vienna’s Department of Evolutionary Biology conducted an extensive review of scientific literature on birthing difficulties in mammals such as cows, sheep, seals, deer, whales, and elephants. The findings reveal that birth complications, including fetal obstruction and maternal death, are widespread and not exclusive to humans.

Among aquatic mammals, for example, whales and dolphins experience instances where calves become lodged during birth despite lacking a rigid pelvic structure. Similarly, terrestrial species like deer and antelope show rates of birth-related mortality comparable to those in certain human hunter-gatherer groups.

Evolutionary Trade-Offs Behind Birth Risks

The persistence of birth complications is explained by evolutionary trade-offs balancing offspring size and survival. Larger neonates generally have higher survival odds post-birth but pose greater delivery challenges. Conversely, smaller offspring may be easier to deliver but face higher mortality after birth.

Species that produce multiple offspring, such as dogs and pigs, encounter a different dilemma: small litters often result in larger pups prone to birth obstruction, while large litters increase the risk of malpositioned fetuses blocking the birth canal. These evolutionary compromises help maintain the prevalence of difficult births across species.

Reframing Human Childbirth in Evolutionary Terms

This research situates human childbirth within a broader biological framework shared by many placental mammals. While humans face a tight fit during delivery due to a large brain and pelvis adapted for bipedalism, other mammals confront their own anatomical challenges. For instance, cows and horses must navigate the simultaneous passage of the head and forelimbs through a rigid pelvic structure.

By demonstrating that difficult births are common rather than exceptional, the study challenges long-held assumptions about human reproductive biology and encourages a wider evolutionary perspective on maternal and neonatal risks during delivery.

Reference: “Humans are not unique: difficult birth is common in placental mammals” by Nicole D. S. Grunstra, 6 May 2026, Biological Reviews. DOI: 10.1002/brv.70174