A really interesting read on the meaning of human in science:
FOR A HIGHLY egocentric species that is exquisitely conscious of both its unusual anatomical structure and its unique way of mentally processing information, the otherwise self-obsessed Homo sapiens has shown remarkably little interest in formally defining itself relative to the rest of the living world. Back in the eighteenth century the Swedish savant Carolus Linnaeus, father of the system of classifying animals and plants we still use today, established the practice of using particular biological features to define each genus and species in his classification. Yet, in the case of our genus Homo —and only in that case—Linnaeus departed from this sensible procedure, casually advising his readers, nosce te ipsum (know thyself).
Even at the time, this exhortation toward introspection might hardly have appeared the ideal approach to biological self-definition. But in practice few cared: after all, Linnaeus’s lexicographer contemporary Samuel Johnson was satisfied with defining man as a human being, and human as having the qualities of a man. Quite simply, everyone then thought they knew that human beings were so different as to require no definition at all.
You might thus be tempted to imagine that, in the century and a half since Charles Darwin pointed out that we are joined to the rest of nature by common ancestry, science might have begun to make some progress toward a biological definition of the human genus. But if so, you would be doomed to disappointment. Scientists are still arguing vehemently over which ancient fossil human relatives should be included in the genus Homo . And they are doing so in the absence of any coherent idea of what the genus that includes our species Homo sapiens might reasonably be presumed to contain.
Which brings us to a grand question. What does it mean to be human?