The Slow-Developing Human – Rationale for a Species of Newborn Motor Morons

Dolphins are born swimming, cattle can walk within hours and lions are able to run within 20 days of birth. Compare this to a human newborn who will require months before he is able to merely sit without support. More advanced skills like running and jumping may take years to develop in a human newborn. As a species, the speed at which our motor skills emerge lags far behind most other species. Despite a slow rate of motor development, we surpass these other animals in intelligence and fine motor skills later in life. What are the reasons for this? Although it may seem paradoxical, our intelligence is exactly the reason for our slow development.

With increasing intelligence comes an increase in brain size. Fortunately for our child-bearing females, humans are born mentally underdeveloped with a brain size that is limited by the diameter of the birthing canal. Newborn infants are nurtured by their mothers and are sheltered from the elements. They are emotionally supported and protected from predators. This has given rise to commonly termed “Fourth Trimester,” the period of time after the child is born, but still requires a supervisory individual for survival. During this period our motor skills develop slowly, while our cognition advances at a pace much faster than any other species.

Cognitive development is what separates us from other species. Take our ability to communicate, for example. Although numerous other animals utilize intricate methods of communication (see Prairie dog alarm calls encode labels about predator colors for a surprising look into the complexity of animal communication), no other method of communication compares to our languages. As humans, we have the ability to communicate not only information necessary for survival, but also the ability to communicate ideas, feelings and abstract thoughts. While this is beyond the capacity of every other animal species, humans are able to comprehend and integrate language within a few years of development. This may be due to the plasticity of our brains at birth. As children, our cortical development occurs as we explore our environment and touch, smell and taste our surroundings. We are capable of determining how our actions impact the world and how the world affects us. Perhaps most importantly, our brains continue to develop as we listen to our parents speak and communicate with one another. Instead of simply aping our parents’ actions and words, our developing brains may allow us to internalize the language as we develop and create cortical connections based on the constant communication around us. Unlike other animals, our development does not end at birth, but rather, is merely beginning.

Another reason that we may appear to develop our motor skills at a slower pace due to our ability to perform complex tasks. Humans have evolved into an animal specifically designed to carry out intricate movements that require an extraordinary amount of fine motor control. Because structure dictates our function, we have many degrees of freedom available at all of our joints. Controlling this motion requires an exceptional amount of coordinated movements in both the large proximal muscles of the trunk and limbs and smaller muscles of the hands, feet and digits. Seemingly simple tasks, such as writing, drawing or standing up straight require the coordinated movement of hundreds of muscles. Learning to control this movement puts humans on a slower rate of development, although the complexity of the movements is much greater than in other species.

Until our anatomy evolves to permit the birth of newborns with a fully developed brain, we will continue to develop motor skills slower than all other animal species. In the grand scheme of things, slow motor development that allows for future intellectual capacity greater than any other species may not be such a bad thing. Our slowly developing brain can be molded by our experiences after we are born, permitting directional development that may not be possible in other species that are born mentally mature.

References

BARRICKMAN, N., BASTIAN, M., ISLER, K., & VANSCHAIK, C. (2008). Life history costs and benefits of encephalization: a comparative test using data from long-term studies of primates in the wild Journal of Human Evolution, 54 (5), 568-590 DOI: 10.1016/j.jhevol.2007.08.012

Slobodchikoff CN, Paseka A, Verdolin JL. Prairie dog alarm calls encode labels about predator colors. Anim Cogn. May 2009;12(3):435-439. doi: