▁of ▁life ▁in ▁the ▁context ▁of ▁his ▁theory ▁of ▁evolution . ▁In ▁On ▁the ▁Origin ▁of ▁Species ▁( 1 8 5 9 ) ▁Chapter ▁IV ▁he ▁presented ▁an ▁abstract ▁diagram ▁of ▁a ▁theoretical ▁tree ▁of ▁life ▁for ▁species ▁of ▁an ▁un named ▁large ▁genus ▁( see ▁figure ). ▁On ▁the ▁horizontal ▁base ▁line ▁hypoth et ical ▁species ▁within ▁this ▁genus ▁are ▁label led ▁A ▁– ▁L ▁and ▁are ▁spac ed ▁irregular ly ▁to ▁indicate ▁how ▁distinct ▁they ▁are ▁from ▁each ▁other , ▁and ▁are ▁above ▁broken ▁lines ▁at ▁various ▁angles ▁suggesting ▁that ▁they ▁have ▁diver ged ▁from ▁one ▁or ▁more ▁common ▁ancest ors . ▁On ▁the ▁vertical ▁axis ▁divisions ▁label led ▁I ▁– ▁XIV ▁each ▁represent ▁a ▁thousand ▁gener ations . ▁From ▁A , ▁diver ging ▁lines ▁show ▁branch ing ▁descent ▁producing ▁new ▁vari eties , ▁some ▁of ▁which ▁become ▁ext inct , ▁so ▁that ▁after ▁ten ▁thousand ▁gener ations ▁descend ants ▁of ▁A ▁have ▁become ▁distinct ▁new ▁vari eties ▁or ▁even ▁sub - species ▁a 1 0 , ▁f 1 0 , ▁and ▁m 1 0 . ▁Similarly , ▁the ▁descend ants ▁of ▁I ▁have ▁divers ified ▁to ▁become ▁the ▁new ▁vari eties ▁w 1 0 ▁and ▁z 1 0 . ▁The ▁process ▁is ▁ext rap ol ated ▁for ▁a ▁further ▁four ▁thousand ▁gener ations ▁so ▁that ▁the ▁descend ants ▁of ▁A ▁and ▁I ▁become ▁four teen ▁new ▁species ▁label led ▁a 1 4 ▁to ▁z 1 4 . ▁While ▁F ▁has ▁continued ▁for ▁four teen ▁thousand ▁gener ations ▁relatively ▁un changed