I found this rather nice meditation on what is is to be human in Gregory of Nyzanzius’ Second Theological Oration, XXII. I reprint it for no better reason than that it appeals to me:
For if I leave everything else alone, and consider myself and the whole nature and constitution of man, and how we are mingled, and what is our movement, and how the mortal was compounded with the immortal, and how it is that I flow downwards, and yet am borne upwards, and how the soul is circumscribed; and how it gives life and shares in feelings; and how the mind is at once circumscribed and unlimited, abiding in us and yet travelling over the Universe in swift motion and flow; how it is both received and imparted by word, and passes through air, and enters with all things; how it shares in sense, and enshrouds itself away from sense.
And even before these questions – what was our first moulding and composition in the workshop of nature, and what is our last formation and completion? What is the desire for and imparting of nourishment, and who brought us spontaneously to those first springs and sources of life? How is the body nourished by food, and the soul by reason? What is the drawing of nature, and the mutual relation between parents and children, that it should be held together by a spell of love?
How is it that species are permanent, and are different in their characteristics, although there are so many that their individual marks cannot be described? How is it that the same animal is both mortal and immortal, the one by decease, the other by coming into being? For one departs, and another takes its place, just like the flow of a river, which is never still, yet ever constant.
And you might discuss many more points concerning men’s members and parts, and their mutual adaptation both for use and beauty, and how some are connected and others disjoined, some are more excellent and others less comely, some are united and others divided, some contain and others are contained, according to the law and reason of Nature.
Much too might be said about voices and ears. How is it that the voice is carried by the vocal organs, and received by the ears, and both are joined by the smiting and resounding of the medium of the air? Much too of the eyes, which have an indescribable communion with visible objects, and which are moved by the will alone, and that together, and are affected exactly as is the mind. For with equal speed the mind is joined to the objects of thought, the eye to those of sight. Much too concerning the other senses, not objects of the research of reason.
And much concerning our rest in sleep, and the figments of dreams, and of memory and remembrance; of calculation, and anger, and desire; and in a word, all by which this little world called Man is swayed.