Sir, It is appalling that in 2008 you still publish articles such as "Africa's greatest challenge is to reduce fertility' (March 14) by John May and Jean-Pierre Guengant. Fertility in poor African countries is high because Africans correctly respond to incentives. They have so many children for the same reason Europeans and North Americans had as many about a century ago. That is, costs are low and benefits are high. Low-mechanisation agriculture being the only economic activity, families need bodies to cultivate land. In the absence of financial markets, parents need kids in order to insure themselves against old-age risk. The costs of education are nil, since there is no education. Women's opportunity cost of having children is close to zero, because that is what they would earn in the market place. Evidence gathered by demographers shows that in the case of currently developed and developing countries, the decrease in fertility rate occurred as the result of change in incentives brought about by economic growth. Fertility in the UK begun falling in around 1890, not because British peasants became educated or acquired advanced contraception methods but because the benefits of having children decreased and the associated costs increased. May and Guengant do a great disservice to African populations by suggesting that the problem lies in the fact that many African women are prevented from getting contraceptives because of "gender inequalities, cultural and religious traditions and inadequate family planning services'. When the fertility rate started falling in Britain, there were no family planning services and there were plenty of gender inequalities. In conclusion, there are very good reasons why, as noted by May and Guengant, "demographic issues are conspicuously absent from the African development debate'. Suggesting that public policies directed towards lowering fertility rates may help poor countries develop is harmful and intellectually dishonest. Gian Luca Clementi, Assistant Professor, Department of Economics, Stern School of Business, New York University, New York, NY 10012, US From Mr Simon V. Potter. Sir, John May and Jean-Pierre Guengant (March 14) get it backwards. Unless we are prepared to have the state impose with force a one-child policy, as China did, or coax vast numbers into sterilisations, as India did, we have to accept that reduced fecundity is not the cause of wealth so much as its by-product. Italy and Qu