2. any living or extinct member of the family Hominidae characterized by  superior intelligence, articulate speech, and erect carriage
		
		
	 
 
  
 This definition has serious problems, at best. 
The two parts of this, taken equally, implies that a human being must be  (ignoring the mention of extinct) both living and have articulate  speech and erect carriage.  If not, no human being.  This would mean  that those born seemingly without the ability to communicate, or those  who cannot walk are not human.  Infants possess none of these  abilities.  I think, rather, that this definition is unfortunately too  ambiguous to be useful.  
 
While I can appreciate that the newly conceived doesn't look anything at  all like an adult, or act like an adult, does not communicate like an  adult or consume the food an adult does, and that there are many  compelling emotional and practical reasons for finding a way for it to  not be human, there just isn't any 
science to support it.  Does  an embryo look like a 3 month, 1 day old fetus, for those that think  abortion is wrong after the 3rd month, does a 3 month old fetus look  like a 9 month old fetus, does a 9 month old fetus (still attached to  the mother in a "paracitic" way) look like a 2 year old, like an adult,  etc.  Do any of them act like the other?  Do any of them eat the same  food or in the same manner?  Do all of them display the same level of  cognizance?  
Regarding the comment about paracitic, until we developed formula, infants were still parasitic.  Did they suddenly gain the right to be protected once they were freed from being attached to their mother?
 
There are many types of developmental processes which that we undergo  until death.  We are not done cooking, even at birth.  The brain is  still growing until, some researchers say, until somewhere between 11  and 15 years old.  We don't stop growing in height until 22 or 23.  We  don't start having the ability to communicate until sometime in utero.   When we become aged, our bodies start degenerating - backwards  development, in a sense.  The process is continuous.
If the newly conceived isn't 
yet human,  what makes it human and  when does that happen?  The definition above will not work unless you  deny human status to many groups.  
And you can't say that the newly conceived is 
less human.  If so, based on what?  Based on the definition above?  If so, people that are handicapped are less human
than people that are not.  If you were once fully human but then were in a crippling accident, do you become less human?  
I am not arguing that their abilities to function 
as humans is not diminished.  It is 
right and good  for us to try to prevent what makes people handicapped or crippled  because it would allow them to act in a way that fully actualizes their  potential as human beings.
Not to mention we would have to have a scale on which we 
grade being human.