Michael Crawford says: In an excellent meeting on 22nd November 2011, David Marsh, winner of the Cleave Cup for 2011, expounded on "The Origins of Diversity":

In all 6 editions of the "Origin of Species", Darwin claims that there were two forces in evolution – natural selection and conditions of existence. Of the two he says the conditions of existence was the most powerful. After finishing the 6th edition, he spent the rest of his life looking for what he called pangenes – these he considered were the tools in the blood whereby information from the environment was sent to the genes to respond to the environmental conditions.
Weismann did not like this as he considered it to be too Lamarckian, so he cut off tails of unfortunate mice for several generations and as they still produced tails he declared the conditions of existence was disproved and wrote a paper call the “All Sufficiency of Natural Selection” . This was the birth of Neo-Darwinism which has been the name of the game since. Sadly he should have known better. What he was testing was the power of mutilation, not condition of existence which Weston-Price and Sir Robert McCarrison both identified in the impact of nutrition on health. After all the Hebrews had been cutting off foreskins for 3,000 years and he should have known that their male children were still born with foreskins!!