Physical characteristics of the Buddha
So, at a later time, while still young, a black-haired young man endowed with the blessings of youth in the first stage of life—and while my parents, unwilling, were crying with tears streaming down their faces—I shaved off my hair & beard, put on the ochre robe and went forth from the home life into homelessness.
It is generally held, including by Bhikkhu Analayo, that the 32 marks are a later addition. Texts such as the Dona sutta (AN4:36) mention seeing one of the marks in the footprint, but comparative studies do not include the wheel mark itself.
The suttas often state these are recognisable by Brahmins trained in such prognostication of a mahapurisa (a great man) who would be either a Buddha or a wheel-turning monarch. There is no reference to non-Brahmins seeing them; in fact in several places in the Suttas, such as in the Samaññaphala Sutta (DN2), the protagonists could not recognise the Buddha when surrounded by other monks, showing a normality in physical appearance (which would certainly not be the case if the 32 marks were present).
Possessing these marks is therefore seen in these suttas as an expert qualification from Brahmins of the Buddha's authenticity and status, and therefore a converting-tool to the Brahmin orthodoxy. Unfortunately, there does not appear to be any clear connection to Vedic or Vedanta texts that would show this to be the case. More investigation is required to give evidence of the 32 marks as recorded as being sourced from Brahmanical or Vedic tradition.
Since early statues and icons of the Buddha do not seem to have these features, it has been proposed by Bhikkhu Analayo that some may have in fact formed from the stonemason or sculptor, particularly the webbed fingers which would protect the delicate fingers of the statues from damage. The fleshy protuberance of the head likewise originally being just a stylistic representation of a top-knot of hair, a common feature of Indian holy men.
It is presently speculative whether the statues were later built with the 32 marks in mind, so that should a qualified Brahmin seeing a statue displaying such characteristics, the Brahmin would want to know to whom the statue represents and be interested in Buddhism. It is likewise speculative later Buddhists produced such iconography to reflect the trend from the Lakkhana Sutta as being a genuine necessity, or that they in fact took symbolic representation of the marks as a means of recollection (Buddhanussati). There are no texts or commentaries to suggest these proposals, however future comparative studies may provide esoteric evidence.
The table below summarizes the causal relations from which each of the 32 signs come about: