Homo sapiens, the scientific name of the human species, is singular. “I am only one Homo sapiens,” you would say. It means, literally, “wise man,” or “knowing man” (sapiens is a present participle), which shows you how full of ourselves we are. In Latin, the plural would be homines sapientes, but in English the plural seems to have settled down to Homo sapiens, the same as the singular.
There is no such term as “Homo sapien.” This frequent error comes from our simplistic English assumption that any word ending in an S must be plural.