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12661 results in History of science

Page 289 of 634

  • CHAPTER VII - ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION OF ORGANIC BEINGS

  • Charles Darwin
  • Edited by Francis Darwin
  • Book:
    The Foundation of the Origin of Species
    Published online:
    07 September 2010
    Print publication:
    20 July 2009, pp 198-213
    First published in:
    1909

  • Summary

    Gradual appearance and disappearance of groups.

    It has been observed from the earliest times that organic beings fall into groups, and these groups into others of several values, such as species into genera, and then into sub-families, into families, orders, &c. The same fact holds with those beings which no longer exist. Groups of species seem to follow the same laws in their appearance and extinction, as do the individuals of any one species: we have reason to believe that, first, a few species appear, that their numbers increase; and that, when tending to extinction, the numbers of the species decrease, till finally the group becomes extinct, in the same way as a species becomes extinct, by the individuals becoming rarer and rarer. Moreover, groups, like the individuals of a species, appear to become extinct at different times in different countries. The Palseotherium was extinct much sooner in Europe than in India: the Trigonia was extinct in early ages in Europe, but now lives in the seas of Australia. As it happens that one species of a family will endure for a much longer period than another species, so we find that some whole groups, such as Mollusca, tend to retain their forms, or to remain persistent, for longer periods than other groups, for instance than the Mammalia. Groups therefore, in their appearance, extinction, and rate of change or succession, seem to follow nearly the same laws with the individuals of a species.

  • CHAPTER IX - ABORTIVE OR RUDIMENTARY ORGANS

  • Charles Darwin
  • Edited by Francis Darwin
  • Book:
    The Foundation of the Origin of Species
    Published online:
    07 September 2010
    Print publication:
    20 July 2009, pp 231-238
    First published in:
    1909

  • Summary

    The abortive organs of naturalists.

    Parts of structure are said to be “abortive,” or when in a still lower state of development “rudimentary,” when the same reasoning power, which convinces us that in some cases similar parts are beautifully adapted to certain ends, declares that in others they are absolutely useless. Thus the rhinoceros, the whale, etc., have, when young, small but properly formed teeth, which never protrude from the jaws; certain bones, and even the entire extremities are represented by mere little cylinders or points of bone, often soldered to other bones: many beetles have exceedingly minute but regularly formed wings lying under their wing-cases, which latter are united never to be opened: many plants have, instead of stamens, mere filaments or little knobs; petals are reduced to scales, and whole flowers to buds, which (as in the feather hyacinth) never expand. Similar instances are almost innumerable, and are justly considered wonderful: probably not one organic being exists in which some part does not bear the stamp of inutility; for what can be clearer, as far as our reasoning powers can reach, than that teeth are for eating, extremities for locomotion, wings for flight, stamens and the entire flower for reproduction; yet for these clear ends the parts in question are manifestly unfit.

Page 289 of 634