TWO years ago, aged 27, I committed to a radical lifestyle choice. Having become a stepfather some six years earlier, and with my wife's blessing, I had a vasectomy.

We discussed my reluctance to have children right from the beginning of our relationship and my partner has come to terms with a cold and inconvenient truth.

I don't want my own biological children when there are already so many to go around. I had been thinking about this quite seriously since late adolescence - some time before Al Gore hurled the ecological debate into the mainstream and well before population and immigration became election issues.

Just as the notion of ''man versus man'' dominated the 20th century, it has become increasingly obvious to me that ''man versus nature'' is the issue of our time.

However, not wanting to appear a fanatic, I rarely speak of my anxiety about overpopulation with friends or family, and yet the prospect of an unsustainable world of 9 billion people by about 2050 scares me to the core.