They may be adorable, but human babies are pretty helpless, especially when you compare them with the newborns of many other animal species. It takes infants a couple of months to hold their heads up and at least six months before they are able to sit up on their own. Most require a few more months before they can crawl, and the average age to take one’s first steps is after a year old. Fully developing speech also takes several years, and children remain largely reliant on help from their parents for much of their first decade of life.
In contrast, many animals produce young that are able to coordinate movement within hours of birth, from giraffes and horses to whales and ducks.
There are numerous reasons why human babies are born so underdeveloped. From an anatomical standpoint, it’s well understood that the maximum size a human infant can reach in the womb is generally limited by the size of its mother’s pelvis. If our brains, and thus our skulls, developed much more during gestation, unassisted birth would be impossible. For humans, nine months is also thought to be around the maximum amount of time that the demands of pregnancy (especially the accelerated metabolic rate) can be sustained by a mother’s body.
Yet our brains require many years of development after birth to equip us with the tools we need to live in a complex society, from communication and reasoning to social interactions. Experts agree that parts of our brain, especially the prefrontal cortex, are not fully developed until we reach adulthood.
Humans are certainly not the only species to produce young that are incapable of caring for themselves from an early age. The relative development of baby animals at birth has to do with factors such as their parents’ anatomy, the requirements of their habitat, and potential threats from predators. For animals that are frequently on the move, it’s especially important for babies to acquire mobility early on.
While it’s not a hard-and-fast rule (and there are notable exceptions, like pandas), larger animals are often born more physically capable than smaller animals. For example, birds that lay larger eggs (like chickens and turkeys) are more developed when they hatch, as the eggs contain more nutrients. Smaller birds that produce smaller eggs will need to spend more time developing in the nest under the protection of their parents. The same is true of many small mammals, which are unable to sustain long pregnancies and sometimes give birth to babies that have not yet grown fur or opened their eyes. Staying warm, fed, and protected in nests, dens, and burrows thus becomes essential.
They grow up so fast...or do they?
- Another difference among species is the amount of information about behavior that is instinctual versus learned from adults. Human babies have a huge amount to learn from their parents and other caregivers about navigating their world, staying safe, and adjusting to the complex demands of society.
- Essentially, it’s an evolutionary trade-off. While it takes humans a long time to progress from infant to child to adult, the end result is an individual capable of complex cognition and abilities unlike any other creature.
- The scientific terminology for differences in maturity at the moment of birth is precocial (those that are relatively mature and mobile) versus altricial (those that are born underdeveloped and need assistance from parents). The term “precocious” is a related term that is commonly used to describe an unusually advanced child, especially in regard to mental development.
