What does it mean to be human? On the surface, this may seem a frivolous question. Isn’t the answer obvious? Here are a few definitions:
Dictionary definition – The Oxford Dictionary defines a human being as a “man, woman, or child of the species Homo sapiens, distinguished from other animals by superior mental development, power of articulate speech, and upright stance.”  Although I think the concept of ‘superior mental development’ needs to be articulated further, I have no real problem with this definition.
Medical definition – J.M. Goldenring, defines a human being in terms of an organism that has a functioning brain. “The brain is the only unique and irreplaceable organ in the human body, as the orchestrator of all organ systems and the seat of personality. Thus, the presence or absence of brain life truly defines the presence or absence of human life in the medical sense.”  He admits, however, to a murky area in which cortical activity is absent and yet subcortical functions remain, as in a “’severe vegetative state’ – a medico-ethical limbo wherein a human is technically still alive or rather ‘not quite dead’ but is no longer capable of higher brain functions.” 
But the limbo to which Goldenring refers, concerns the difference between life and death. Does consciousness matter in defining a human being? Is self-awareness necessary for human consciousness? Flipping this question on its head, is someone with no self-awareness considered human? Is there a test for this self-awareness? These are also important questions ethically and morally. The answers have consequences in the way society treats those that it doesn’t understand or those who cannot contribute to the goals of society.
Cultural definition – Cultural definitions of humanness can be traced back to different creation stories and the placement of mankind in relation to life in the rest of the natural environment.
Creation stories in different cultures
There is a long history of thought that the human being is the apex of creation. Genesis (1:28) mentions that humans are superior to the rest of the animal kingdom when God blesses Adam and Eve saying “Be fruitful and multiply, fill the earth and subdue it, and have dominion over the fish of the sea and over the birds of the sky, and over every living thing that moves upon the earth.” 
American Plains Indians have similar stories of creation to that found in Genesis. Since animals were created prior to human beings, they were deemed closer to the Great Spirit, thereby commanding respect and veneration. This helps us to understand the importance of communicating with their god, through animal spirits. 
Placing life forms in order
The classification and ranking of the order of life dates to Aristotle (384-322BC). Aristotle’s History of Animals classified organisms hierarchically, placing them according to complexity of structure and function.  This ‘great chain of being’ (in Latin: scala naturae, or “stairway of nature”), ranked all matter and life. “The chain starts from God and progresses downward to angels, demons (fallen/renegade angels), stars, moon, kings, princes, nobles, men, wild animals, domesticated animals, trees, other plants, precious stones, precious metals, and other minerals.” 
A small step for man
In medieval times, the concept of the ‘great chain of being’ was applied to subdividing humanity into groups or races. The classifiers at that time noted common physical and character qualities among groups that distinguished them from others. “Society gave different values to those differentiations, which essentially created a gap between races by deeming one race superior or inferior to another race, thus a hierarchy of races. In this way, science was used as justification for unfair treatment of different human populations”.  Historical examples of this unequal and deadly treatment abound throughout history.
Is there hope?
It is safe to say that the rank and file of each cultural group values its own members above those in other groups. Indeed, Dr. Wolf Wolfensberger  developed a means of analyzing human relationships called Social Role Valorization (SRV). “The theory is based on the idea that society tends to identify groups of people as fundamentally ‘different’, and of less value than everyone else. It catalogs the methods of this ‘devaluation’ and analyzes its effects. It may be used by those seeking to counteract these methods and effects” [emphasis added] 
What about those with differing abilities?
Mistreatment of this category of people, which cuts across racial lines, has also been rampant through the centuries. For example, those with greater, or misunderstood abilities have been burned at the stake in American history. Those with lesser mental or physical abilities have been marginalized at best and at worst, hounded and bullied.
I am sad to report that I, myself have heard medical doctors in a major city medical center refer to some of their patients as SHPASs. This stands for Sub Human Piece of Shit. Excuse the vulgarity, but I didn’t make up this reprehensible view of a segment of humanity, and I don’t know the criteria by which the doctors classified these patients.
Does the definition of humanness matter?
Yes it does. How society sees an individual matters quite a bit. More importantly, the denial of humanity to certain groups has familiar consequences. To classify those who do not understand; those who cannot communicate and those who are physically different or disfigured as less than human gives those who consider themselves superior license to abuse, misuse or even destroy, with impunity.
Aside from the moral repugnance of this idea, each and every one of us is just one blow to the head away from this class of people.
 Goldenring, J.M. The brain-life theory: towards a consistent biological definition of humanness Journal of Medical Ethics, 1985, 11, 198-204 print
 Ibid pg 200