concept

Discount rate

The rate at which a sum of money in the future counts as worth less than the same sum today. It reflects not emotional impatience but opportunity cost: money received now can be invested elsewhere and earn a return on its own. For a living resource this number is the hinge of the whole problem, because it is measured in the same units as biological growth. If a population grows faster than the discount rate, leaving the animals in the wild is itself the better investment. If the discount rate is higher, waiting becomes a loss — and then it is the financial arithmetic, not cruelty, that recommends taking everything now.