Retail therapy has long been a treat for millions of women who enjoy nothing better than a trawl round the shops. For those who pause long enough to wonder if it is nature or nurture which guides them, the answer may have emerged. Sales levels indicate that it is behaviour that is learned, so it may be down to women's mothers that they like to shop so much. Figures have revealed that clothes for baby girls out-sell those for boys by a fifth. It emerged that by the age of four, girls have 20 percent more clothes than boys of that age. As mothers buy most of the clothes for their children, this suggests that they instinctively instill a much greater need for clothes in their daughters from a very young age. As a result, it is likely that women are brought up to love shopping through years of intense exposure to fashion and purchases. The Debenhams sales results have been interpreted by Dr Karen J. Pine, Professor of Developmental Psychology at the University of Hertfordshire. 'Human society puts a great deal of emphasis on female appearance and this will inevitably result in more clothes being purchased for girls than boys,' she said. 'Parents encourage the importance of clothes through leisure activities such as shopping and play that involves dressing up. 'While dads are taking their sons out for football matches, women are taking their little girls shopping and encouraging them to take an interest in fashion.'