So that some can succeed.
My take on this, developed in my OU Blog and shared here in due course relates not to physical differences, but to character. i.e. the ability or not of people to succeed or fail in current circumstances. Who in a cataclysmic disaster, for example, is going to survive, the undernourished tramp or the overweight, unexercised City Banker?
Uncertainty principle: How evolution hedges its bets – life – 10 January 2011 – New Scientist