I've seen a similar view (the one about our genetics) expressed by the outspoken (and occasionally controversial) Richard Dawkins in The Selfish Gene and I personally find it quite plausible -- our genes define the structure of our organs and their functions, including our neurology, which defines everything that we are or could be as a conscious entity. It's an established fact that our genetic structure changes throughout our life -- we very literally change not just as a "person" but on a more fundamental level, as a living organism.

I have anecdotal evidence of my own personality changes as a result of recovery from hormonal/dietary disbalance I've experienced in my life, but that's another story. :)