Atavism in Guinea-Chicken Hybrids 743 
dark today as in the time of Darwin, despite the new impetus given 
to the study of the problems of hereditary through the renaissance 
of the Mendelian principles. In such cases, as I have suggested 
elsewhe1e," we appear to get entirely outside the pale of minor 
so-called “unit characters” which may be juggled to and fro from 
generation to generation, and to face an entirely different propo- 
sition; namely, that of the more fundamental and the more super- 
ficial respectively, of the more permanent as against the more 
fluctuating. ‘The upsetting of a breed by hybridizing or mongrel- 
izing may bring about in successive crosses, seemingly, a more or 
less systematic reversal of the process of construction of a given 
pattern; the regression proceeding for the most part from the 
latest additions to the less recent until finally a form closely ap- 
proaching that of the primitive ancestor appears. Thus, for 
example, may be cited the results of Ewart'* who found that in 
pigeons, when owl and archangel were crossed, the latest colors 
added by the fancier were not reproduced but older and simpler 
colors became visible again. When this mongrel was further. 
crossed with a white fantail all recently acquired colors were lost 
and the primitive ancestral type as seen in the wild rock pigeon 
was almost completely reproduced. Crosses from such widely 
separated forms as guineas and chickens seem to undo at one 
stroke most of the recent accumulations of each species. 
Possibly part of the explanation lies in this, that having diverged 
from a common stock the parents of such hybrids have certain 
fundamental features and tendencies in common, which as a 
result of the physiological processes of growth and development 
can come ultimately to a definite objective expression as they did 
in the original common ancestor. On the other hand, certain 
traits acquired since their divergence from the parental stock have 
become so dissimilar and incompatible in the two forms that as 
a result of hybridization they annul one another and thus permit 
this unmasking, as it were, of old characters. Doubtless certain 
characters not represented in the opposite species or certain non- 
antagonistic characters may also manifest themselves. 
‘8 Guyer, M. F.: The Insufficiency of the Chromosome-Theory of Heredity. Proceedings of the 
International Congress of Zodlogists for 1907. 
14 Ewart, loc. cit. 
