Diane asks: “How did Beorn come about? Is he truly a man or something more because he can turn into a bear?”
Beorn’s nature is one of those things which is never really addressed in The Hobbit. In that volume there is this passage, spoken by Gandalf.
He is a skin-changer. He changes his skin: sometimes he is a huge black bear, sometimes he is a great strong black-haired man with huge arms and a great beard. I cannot tell you much more, though that ought to be enough. Some say that he is a bear descended from the great and ancient bears of the mountains that lived there before the giants came. Others say that he is a man descended from the first men who lived before Smaug or the other dragons came into this part of the world, and before the goblins came into the hills out of the North. I cannot say, though I fancy the last is the true tale.
Chapter VII – Queer Lodgings, The Hobbit
References are made to the people of Beorn at several points in The Lord of the Rings.
It was in forgotten years long ago that Eorl the Young brought them out of the North, and their kinship is rather with the Bardings of Dale, and with the Beornings of the the Wood, among whom may still be seen men tall and fair, as are the Riders of Rohan.
Chapter 2 – The Riders of Rohan, The Two Towers
Most of the Men of the Northern regions of the West-lands were descended from the Edain of the First Age, or from their close kin. Their languages were, therefore, related to the Adûnaic, and some still preserved a likeness to the Common Speech. Of this kind were the peoples of the upper vales of Anduin: the Beornings, and the Woodmen of Western Mirkwood; and further north and east the Men of the Long Lake and of Dale.
Appendix F – Of Men, The Lord of the Rings
Finally we have this sentence from one of Tolkien’s letters.
Though a skin-changer and no doubt a bit of a magician, Beorn was a Man.
Letter no. 144, 25 April 1954, The Letters of J.R.R. Tolkien
Taking all of this in—from Gandalf’s musings in The Hobbit, to multiple references to the Beornings, and finally a straightforward statement in a letter to Naomi Mitchison—I think it can be said with no equivocation that Beorn was a man, descended of men and father to men.