At last, you have broken the taboo on discussion about regulating family size. ("Beckhams a bad example for families", News, last week). It is everybody's business when 75 million people are added to this planet every year, when the average north American consumes five times the amount of resources the Earth can sustain, (three times in the UK), when rising seas are becoming barren and other species increasingly give up the struggle to compete with mankind, who continues to foul the atmosphere and strip out the natural world.

In October, human population will exceed seven billion – no cause for celebration. Despite the fact that reliable contraception is easily available, in the developed world at least, 40% of pregnancies are unplanned. How can this be so? In addition, many third and subsequent pregnancies are a deliberate attempt to produce a baby of the opposite sex, all adding logarithmically to the continuing expansion of man.

To paraphrase David Attenborough, it is impossible to think of one single environmental problem that we face, where stabilisation of population size will not make the solution more achievable.

Wake up, developed world, and think of our grandchildren.

Penny McKee

Edinburgh

Neo-Malthusian outfits, such as the Optimum Population Trust, with their green friends, jump at any opportunity to peddle their half-truths on population growth, which have been around since the Malthus theorem was disproved many centuries ago.

What they refuse to acknowledge is that the fertility rate of half the world is now 2.1 or less, the magic number consistent with stable population. This number is expected to fall below this level between 2020 and 2050.

This is not surprising, as poor countries are going through the same demographic transitions that rich ones went through, but at an earlier stage in their development and much quicker, making the anticipated fall in ratio an unfortunate inevitability. The Trust should keep its prejudices against the human race to itslef.

Murad Qureshi

London Assembly

Greater London Authority

City Hall, London SE1

I am writing to applaud Caroline Lucas for raising the taboo subject of population. I am closely involved with several development and environmental charities. My experiences of travelling off the tourist trail in Africa and of seeking to protect wildlife closer to home have led me to conclude that we are never going to be able to solve the many human-induced declines of both plant and animal species, nor really conquer poverty, unless we do something to stop the inexorable growth of the human population towards nine billion people.

Those who really want a good future for their children and grandchildren should surely understand that if we keep reproducing and living at an unsustainable rate, we will not only exceed the capacity of the world to sustain us but also cause mass extinctions of our fellow species.

There's a desperate need for greater access to contraception for all women in developing countries and for a change in social attitudes to large families in developed countries.

Let's hope Caroline Lucas's timely call for action will prompt a rational debate on this issue instead of the usual mud-slinging.

Jennie Lang

Richmond, Surrey

I read that there have been criticisms of the Beckhams and other prominent couples for their failure to be proper role models, owing to their irresponsibility in producing four children. Does the same criticism, I wonder, apply to our head of state and her consort?

Monica Jones

Stockport, Greater Manchester