In the future there will be no more human beings. This is not something we should worry about.-- writes John Harris (in Who’s afraid of a synthetic human?). And having got your attention he frames an argument for human enhancement with a plausible simile: it's like candlelight as opposed to darkness -- artificial, of course, but an unquestionable benefit (...so long as it regulated and fairly distributed: Harris is after all a European  not an American).
For Harris, professor of bioethics at Manchester University, "the end of humanity is not in itself a concern; making sure that those who replace us are better than we are is a huge and timely concern."
I agree with Stephen Pinker's attack on 'theocon bioethics', provocatively titled The Stupidity of Dignity, and I think Olivia Judson writes thoughtfully and informatively about how, for her, wonder replaced unease when she learned more about cybrids. But I think we need to think carefully about two terms Harris deploys: "better" and "humanity."
In the brief scope of his article, Harris describes "creatures better than ourselves" as ones that are "longer-lived, more resistant to disease and injury, healthier and better adapted to a changing environment". This is OK as far as it goes but I think it is not enough for at least two reasons.
One, we are not just talking about pet dogs or heirloom vegetables (to use a comparison made in a post on the blog Practical Ethics). Synthetic biology looks likely to have greater potential than anything so far to turn all beings into an undifferentiated "standing reserve" (Heidegger) for any use to which humans -- or post humans -- choose to put them.
Two, we need an enhanced sense of what it is to be human and a broader and deeper sense of non-human being at least as much as if not more than we need enhanced humans. I have in mind wisdom and compassion -- 'humanity' in the richest sense of that word -- and a better sense of moral and physical limits, given our capacity to inflict pain on others and to damage ecosystems.
In a recent piece titled Faustian Economics, Wendell Berry writes:
Our cultural tradition is in large part the record of our continuing effort to understand ourselves as beings specifically human: to say that, as humans, we must do certain things and we must not do certain things. We must have limits of we will cease to exist as humans; perhaps we will cease to exist [altogether]. At times, for example, some of us humans have thought that human beings, properly so called, did not make war against civilian populations, or hold prisoners without fair trial, or use torture for any reason.[Footnote 1: 'European', perhaps, in the sense of states, institutions and values of the kind that the historian Tony Judt hopes for: "the alternative in the 21st century is not the globalised post state world as versus the old fashioned world of the nation state; it's the protective, welfare state -- democratic and open -- as against the demagogic closed state of fear." (Nightwaves, BBC Radio 3, May 2008)].