The Descent of Man

With mammals, when, as is often the case, the
sexes differ in size, the males are almost always
larger and stronger. I am informed by Mr.
Gould that this holds good in a marked manner
with the marsupials of Australia, the males of
which appear to continue growing until an
unusually late age. But the most extraordinary
case is that of one of the seals (Callorhinus ursinus),
a full-grown female weighing less than
one-sixth of a full-grown male. (36. See the very
interesting paper by Mr. J.A. Allen in 'Bull.
Mus. Comp. Zoology of Cambridge, United
States,' vol. ii. No. 1, p. 82. The weights were
ascertained by a careful observer, Capt. Bryant.
Dr. Gill in 'The American Naturalist,' January,
1871, Prof. Shaler on the relative size of the
sexes of whales, 'American Naturalist,' January,
1873.) Dr. Gill remarks that it is with the polygamous
seals, the males of which are well
known to fight savagely together, that the sexes
differ much in size; the monogamous species
differing but little. Whales also afford evidence