They don't have the muscles or nerves or the connection between them? All three? Animals can walk within days, most of them. I read somewhere that some part of the motor system doesn't mature till the person is in their 20s! That can't be true, but unfortunately I can't find any information on this question. I've done all sorts of google searches, for things like "newborn" "motor neurons" "motor cortex" "muscles" "walking" etc. I had not success. Appreciate any help.
...Humans are born with very few innate behaviors and instincts. For example, whereas many animals (insects, fish, reptiles, amphibians, etc.) are fully capable of walking, feeding themselves and even surviving independently after birth, human babies can do practically nothing after birth and cannot survive without a caretaker. The difference here is that the DNA of humans does not specify a wiring diagram for the brain. Rather this wiring diagram is formed in response to the experiences of the individual. For example, if you were to take a newly born baby and cover its eyes for a critical period in childhood, the child's neural circuitry for interpreting visual stimuli would not develop properly and the child would be blind despite the fact that the child's eyes work perfectly well. Another consequence of this strategy is that everyone will develop different neural circuits to perform the same functions. For example, whereas the same nerve cell will trigger the same escape response in all flies, activating a specific nerve in humans would likely trigger very different responses in different individuals.
While this wiring-on-the-fly strategy has many disadvantages in the younger phases of life (babies and children are very much dependent on others for survival), this plasticity of the brain associated with the wiring strategy gives humans an unparalleled ability to learn. This neural plasticity is likely one reason why humans can learn complex tasks like reading and writing while other organisms cannot.
Thanks for the replies everyone.
As far as this response, where can I learn more about this, about various ways our development lags behind other animals, and also in what particular way.
[In mice], the axonal branching structure of each motor neuron was unique. We compared each axon with its functional counterparts, as defined by the size principle, in other muscles, and found substantial topological differences. Left-right pairs of corresponding neurons in the same animal showed no less variation than ipsi- or contralateral pairs from different animals. Such intra-animal variance is surprising, as each pair of neurons had identical genetic background and presumably experienced an identical environment. This result suggests that the branching pattern of these neurons was not predetermined, which contrasts strongly with the situation in invertebrates. For instance, the C. elegans connectome revealed remarkable stereotypy in the structure of the neural circuit. Worm neurons that are ontogenetic counterparts share almost identical branching patterns and connectivity both within an individual and across different animals, even though they may not be exact replicas of each other [18,19]. In annelids [55,56], insects [57–62], and crustaceans [63,64] individual neurons can also be identified, and their axonal branching patterns are stereotyped. In particular, this mammalian result contrasts with the stereotypy of neuromuscular innervation in invertebrates. For example, although there are fine structural differences in the terminal branching of axons at NMJs of any particular muscle fiber in insects, even these branches seem to have morphological regularities that are recognizable between different animals [65,66]. In mammals not only is the preterminal branching highly variable (as shown in this paper), but our experience suggests that no two NMJs look the same. Thus axonal branching in this mammalian system seems fundamentally different from that found in invertebrates.
Here are simple explanations of basic skills and abilities human babies need to acquire before they can walk (the more complex explanations of how these occur neurologically are explained above).Don't miss the mechanical perspective. A standing person is a good example of an inverted pendulum, which get easier to balance with increased length/height.
Overall, though, my money is on lack of strength. Newborns can't lift their own heads. They've got no business walking.
Up to about 3 months of age, babies' eyes do not focus on objects more than 8 to 10 inches from their faces.
Depth perception, which is the ability to judge if objects are nearer or farther away than other objects, is not present at birth. It is not until around the fifth month that the eyes are capable of working together to form a three-dimensional view of the world and begin to see in depth.
Most babies start crawling at about 8 months old, which helps further develop eye-hand-foot-body coordination. Early walkers who did minimal crawling may not learn to use their eyes together as well as babies who crawl a lot.
By the age of nine to twelve months, babies should be using their eyes and hands together.
At around 9 months of age, babies begin to pull themselves up to a standing position.
It has been observed by scientists that motor skills generally develop from the center to the body outward and head to tail. Babies need to practice their skills; therefore they will grow and strengthen better. They need space and time to explore in their environment and use their muscles. “Tummy-time” is a good example of this. At first they are only able to lay their belly on the floor but by around two months they start to gain muscle to raise their head and chest off the ground. Some are also able to go on their elbows. They will also start to kick and bend their legs while lying there, this helps to prepare for crawling. By four months they are able to start to control their head and hold it steady while sitting up. Rolling from belly to back movements is started. At about five months the baby will start to wiggle their limbs to strengthen crawling muscles. Infants can start to sit up by themselves and put some weight on their legs as they hold onto something for support by six months. Around ten months they should be able to stand on their own.