He pointed to the changes wrought on domesticated organisms by the artificial selection of similar variations, and drew the inference that there must be parallel occurrences under wild nature.
Later observers have found similar occurrences in the cases of small nematodes, rotifers and bacteria.
Among other occurrences of the name of Avon in Great Britain there may be noted - in England, a stream flowing south-east from Dartmoor in Devonshire to the English Channel; in South Wales, the stream which has its mouth at Aberavon in Glamorganshire; in Scotland, tributaries of the Clyde, the Spey and the Forth.
He, moreover, sought in the events of his own life a verification of the theory of planetary influences; and it is to this practice that we owe the summary record of each year's occurrences which, continued almost to his death, affords for his biography a slight but sure foundation.
Both narratives are doubtless based upon actual occurrences - the cures narrated in Mark ii., iii., viii., x.