Is a prior human existence required for a current/subsequent human existence? If I, this impermanent and suffering and no-self array of aggregates, am journeying through this human realm now, shall I assume that that which was "my prior life", another impermanent and suffering and no-self array of aggregates, was also journeying through the human realm (i.e. a prior human existence is a prerequisite for a subsequent human existence)? I am inclined to think that it is possible for an individual array of ever-fluxuating potentialities to "pass" through the human realm consecutively a number of times.
As I see it, if we assume a linear, unidirectional temporality, it is logically impossible that a prior human existence be necessary for a human existence since there could never be a first existence. 

Concerning the beginnings of existence, according to, e.g., the Assu Sutta:


  "A beginning point is not evident, though beings hindered by ignorance
  and fettered by craving are transmigrating &amp; wandering on." 


According to Buddhism, it is not only possible to be reborn as a human many times but, as I take the Mata Sutta to declare, certain that each person has:


  A being who has not been your mother at one time in the past is not
  easy to find... A being who has not been your father... your
  brother... your sister... your son... your daughter at one time in the
  past is not easy to find.


I cannot think of any specific references about consecutive human births in the Pāli Canon, but one may, given the appropriate conditions, e.g., having practised generosity, achieve their desires for some kinds of birth. So, it seems that one could theoretically be reborn several times in a row as a human if they desired it and accomplished the necessary conditions. (cf. AN 8.35)