The age of minerals determined by radioactive methods agrees roughly with the age of the galaxy. This suggests that radioactive alpha-decay constants have probably changed by less than a factor of 3 or 4 during the last 3 or 4 × l09 years. It is shown that this implies that many ‘Constants of Nature’, particularly e, h and c probably change more slowly than 10−12 parts per year. The meson coupling constant also appears to change more slowly than this and (...) the beta-coupling constants by less than 10−9 parts per year. (shrink)