atavism

etäisperinnöllisyys, atavismi The reappearance of an ancestral characteristic in an organism after several generations of absence.
(quote-book)
The recurrence or reversion to a past behaviour, method, characteristic or style after a long period of absence.
puhekieltä Reversion to past primitive behavior, especially violence.
1933, (w), (w), Chapter XXXVI, http://www.gutenberg.net.au/ebooks01/0100171h.html

I have even read in a book of criminology that the tramp is an atavism, a throw-back to the nomadic stage of humanity.