In terminology, human being is a commonly used, but ill-defined, term or expression for a type of molecular structure called "human" that is argued to posses the properties of a “being” and to take part in the evolutionary process. The difficulty in using this term is that the idea of life or a “human being”, when viewed from the molecular evolution table perspective, is a fictional construct that falls apart in definition as one descends down the evolutionary tree to the roots, which are comprised of hydrogen atom precursors.  In this sense, the conception of a person as a “human molecule” becomes a more logical and correct perspective. 
1. (a) Thims, Libb. (2007). Human Chemistry (Volume One). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two). Morrisville, NC: LuLu.
2. Thims, Libb. (2008). The Human Molecule (issuu) (preview) (Google Books) (docstoc). LuLu.