Natural soil fertility is dropping in many areas because of continuous industrial fertiliser and pesticide use, while the growth of algae is increasing in lakes because of the fertiliser run-off.

Despite their "natural" origins, they are not free of potential side effects, such as high blood pressure, digestion trouble, fertility problems and depression.

Since those who cannot breed are, evolutionarily speaking, dead already, natural selection does not usually design bodies that outlive their own fertility.