"When one looks carefully at a biological problem, one can usually discover
more than one causal explanation. ... Such pluralism of beliefs presents a
problem for both verification and falsification. Producing evidence for
natural selection would not necessarily falsify the inheritance of
acquired characters, and falsification of the inheritance of acquired
characters would not necessarily leave natural selection as the only other
possible cause of evolutionary change.
Curiously, pluralism in biological explanation was much better appreciated by the old-time naturalists than by modern specialists. ... Indeed it is quite possible that in biology the majority of phenomena and processes must be explained by a plurality of theories. A philosophy of science that cannot cope with pluralism is not suitable for biology."
(Mayr 1997, p.67-68)