Popular evolutionary hypothesis fails

Arthur V. Chadwick (chadwicka@swau.edu)
Thu, 07 Oct 1999 09:46:09 -0700

Does climatic change drive mammalian evolution?

Donald R. Prothero, Department of Geology, Occidental College, Los Angeles,
CA 90041, prothero@oxy.edu


Neo-Darwinian evolutionary theory argues that species and faunas are
exquisitely adapted to their environment and should respond when their
habitat changes. To test this hypothesis, the mammalian re- sponse to four
of the largest climatic events of the Cenozoic (as documented by the marine
record, oxygen isotopes, land plants, and other climatically sensitive
organisms) are examined. These events occurred during the global cooling at
the end of the middle Eocene (37 Ma), the cooling and drying event in the
earliest Oligocene (33 Ma), the spread of C4 grasslands in the late Miocene
(7 Ma), and the rapid climatic fluctuations of the PliocenePleistocene (2.5
Ma to present). In each case, there is relatively little short-term
response of the mammalian fauna. Typically, there is a greater turnover
millions of years before and after the time fo climatic change than during
the climatic event itself. This pattern suggests that the climatic control
on mammalian evolution is much more complex than previously supposed, or
that intrinsic biotic controls may be more important than extrinsic
environmental controls.
GSA Today 9:1-7 1999