In article ,
Geraard Spergen wrote:
C12 is 99% of all carbon, C13 is 1%, and C14 is about 1 part per 10^12.

Plants naturally have more C13 than animals so any substance (including
testosterone) produced from plants will have a higher C13 proportion
than the same substance produced by animals. Hard to believe there's
any difference in chemical reactions, it's probably due to photosynthesis.

What is photosynthesis if not a chemical reaction? At
least make your beliefs consistent. I suggest you take up
creationism. If that is not to your liking you will have
to eat your beliefs, because we have known for many
decades that chemical reaction rates for C12, C13, and C14
are different.

--
Michael Press