868 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
the American Museum of Natural History, New York, in the order of 
succession in time as determined by the strata from which the fossils 
had been taken. Oneseries showed the most gradual and continuous 
modification in the characters of teeth, another a similarly continuous 
evolution of horns. 
Again, the well-known fossil Archaeopteryx, found in a series of 
slates in Germany, would certainly seem to constitute a lnk between 
groups now widely separated by divergence in evolution from the 
same ancestors. This animal is at once a feathered flying reptile 
and a primitive bird with many reptilian structures. Although 
Archaeopteryx was a primitive bird, it is in a true sense a ‘‘link”’ 
between reptiles and the group of modern birds; the gap between 
these types is filled up by fossil forms like Hesperornis, whose remains 
are found in strata of a later date. ‘‘That these links are not unique 
is proved by numerous other examples known to science, such as 
those which connect amphibia and reptiles, ancient reptiles, and 
primitive mammals, as well as those which come between the differ- 
ent orders of certain vertebrate classes. The important element in 
these examples of evolution is, first, their adaptation; secondly, the 
origination of new parts, and thirdly, the retention of the better 
invention.” ! Evidence of this kind does not enable us to decide 
upon the cause of evolution; but in the instances referred to pro- 
gressive development has occurred gradually, and not by mutation 
or sudden leaps.? On the other hand, they have much to do with 
the building up of the fittest. As Darwim states: ‘‘The tendency 
to the preservation (owing to the severe struggle for life to which 
all organic beings at some time or generation are exposed) of any 
variation in any part, which is of the slightest use or favorable to 
the life of the individual which has thus varied, together with the 
tendency to its inheritance. Any variation which was of no use 
whatever to the individual would not be preserved by the process 
of natural selection.” * 
Another kind of evidence favoring the idea of the progressive 
evolution of human beings from simpler orders of animals is the 
presence of what are known as nonfunctional vestigial structures, 
relics of past phases of existence, such, for mstance, as the unused 
external muscles of our ears and rudimentary third eyelids; the 
gill-clefts of reptiles, birds, and mammals, and the hind limbs of 
whales. The study of these vestigial structures is of importance 
in showing that ancestral features have great power of hereditary 
1 The Doctrine of Evolution, by Prof. H. E. Crampton, p. 99. 
3. B. Poulton, The Quarterly Review, July, 1909, p. 18. 
3 More Letters, 1. Pp. 126. Quarterly Review, July, 1909, p. 26. Also The Evolution of Living Pur- 
posive Matter, by N. C. Macnamara, vol. 97, International Scientific Series, pp. 2, 53. 
