The characteristics and behaviours of F1f (the female hybrid of
Trachypithecus leucocephalus
and
T. francoisi) and its backcross offspring (Be1， Be2， Be3 and Be4) were extensively observed. The results showed that the hybrid F1f and its offspring had similar characteristics with
T. francoisi. Besides the black hair was an overwhelmingly dominant character, the changing of their hair colour, the breeding behaviour of hybridized F1，and the growing process and behaviours of the hybrid F1f offspring resembled
T. francoisi. However the feature of
T. leucocephalus was nearly not present in the hybrid F1 and its offspring, excepting that in the development process the time for their hair colour change was longer and during their growth there existed imprinting phenomenon of
T. leucocephalus. Therefore it can be inferred that the gene control of
T. leucocephalus only played a supporting role and
T. francoisi's gene dominated in the hybrid F1f and their offspring. The percent of weak infants for backcross langurs reaching 50%, which was higher than that of the general 10%-20% of
T. francoisi, suggested a sign of outbreeding depression. Based on our observation that the hybrid F1f was able to reproduce its offspring successfully we can make a conclusion that
T. leucocephalus should be considered as a subspecies of
T. francoisi instead of an independent species.
