Give both a man and a woman the task of buying a pair of pants, and a credit card. Most likely, the result will be quite different in terms of shopping time and money spent.
Declan Chellar takes an anthropological approach at an explanation of this phenomenon:
Now my understanding is that both physiologically and psychologically, the human race hasnt changed much since our ancestors were hunter/gatherers, so when I am trying to understand any particular aspect of human behaviour I hold it up against the mirror that is our ancestry and see how it reflects.
The findings that he documents in Shopping: The male / female divide explained are very plausible. :-)
(via Fortify your Oasis)