If you're going to use the scientific definition of "human" to set policy, then you need to explain why it's ethically wrong to kill any organism that is biologically "human."
Declaration of Independence:
When in the Course of
human events it becomes necessary for one people to dissolve the political bands which have connected them with another and to assume among the powers of the earth, the separate and equal station to which the
Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.
We hold these truths to be
self-evident, that all men are created equal, that they are endowed by their Creator with certain
unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. —
That to secure these rights, Governments are instituted among Men,
The Constitution of the United States of America:
We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and
secure the blessings of liberty to ourselves and our posterity, do ordain and establish this Constitution for the United States of America.
Mirriam-Webster on-line Dictionary
One entry found for posterity.
Main Entry: pos·ter·i·ty
Pronunciation: pä-'ster-&-tE
Function: noun
Etymology: Middle English posterite, from Anglo-French pusterité, from Latin posteritat-, posteritas, from posterus coming after
1 :
the offspring of one progenitor to the furthest generation
2 :
all future generations 
