![]() “The compromise between a narrow birth canal and a big-brained baby is to have the babies early.” Our bodies go one step further to ease childbirth by keeping infant skeletons slightly squishier and more flexible so they can squeeze through the delivery process. A less-developed baby meets both demands, Steele says. But walking pressures our hips to stay narrower. In theory, we could use a wider pelvis to make birthing that large head easier. Read More: Why Don't Apes Have Bigger Brains? At the same time, we have big brains: Our organ is about seven times bigger than it is in other similarly-sized animals. Our hips are narrower than in other primates to keep us from waddling side to side while walking. For one, we move around on two legs with our hands free to hold tools, something not all our ancestors can claim. ![]() Similar to other species' need to stand right away, our inability to do much at all as newborns is a byproduct of other biological needs. Even the different bones that make up our skull have yet to fuse together. When we are born, the shafts of our longer bones hold a lot of soft, flexible cartilage, and many joints are separated. But in other ways, human infants are drastically different.Ī full 15 percent of a human baby’s body weight is fat - a higher percentage than in any other species. The cells, which stretch the length of every individual muscle they are in, only grow wider and longer as we age. Like in other mammals, all the muscle cells we’ll ever have are present when we are born. “Our babies are born exceptionally underdeveloped.” “Personally, maybe it’s the anthropologist in me coming out - we are very much mammal, but we’re also kind of a very weird mammal,” says Teresa Steele, a paleoanthropologist at the University of California, Davis. Humans are born with capabilities and characteristics that look the most different from what we become as we mature. Animals that hunt other animals typically require more time to develop coordination and motor skills, abilities they need to protect themselves and capture their food. In these animals, it takes time for newborns to open their eyes, let alone walk. They don’t have to worry about escaping another species’ claws. Atop the food chain, these predators can take a more leisurely pace when it comes to growing up. Wolf pups or tiger cubs look and behave a lot different a few days after birth. “If you look at a foal when it's born, it looks like skin and bones,” Reed says - hardly any fat and just the little amount of muscle development it needs to move limbs. After gestation, these babies emerge with a higher percentage of bone and muscle making up their body weight, Reed says, so the baby has the equipment it needs to stand up. The ideal accommodations and conditions for early-walking animals typically starts in the womb. And though domesticated animals like cows aren’t often hoofing it to avoid being eaten, their wild ancestors likely did. The sooner a newborn can outrun a predator, the better their odds of survival. But savannas and grasslands offer minimal hiding spaces. Forest-dwelling species can tuck their young into the foliage and trust that it will be safe without supervision for a while - that’s what mother deer do with fawns for days at a time. “We see a lot of prey animals that are precocial, which means that they can stand and move fairly soon after birth,” Reed says.įor wild animals like zebras and giraffes that live in wide-open spaces, the only real defense they have against predators is to run. Those shaky first steps from a lamb or calf serve a purpose: To evade predators.
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