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‘Evolution’ in contemporary discussions denotes the theory of
the change of organic species over time. Prior to the second
half of the nineteenth century, the term was used primarily, if
not exclusively, in an embryological sense to designate the
development of the individual embryo. Since the writings of
Herbert Spencer (1820–1903), and particularly since the
publication of Darwin's Origin of Species in 1859, the term has
been used to designate historical alterations of species. This
meaning of the term also covers two primary forms of species
evolution: (a) progressive linear historical changes of species
from simple to complex forms, such as can be found in Jean-
Baptiste Lamarck's theory of evolution (1809); (b) branching
species change from common ancestors as formulated by Darwin in
1859. Since Darwin's work, evolution has been typically linked
with the theory of natural selection as the primary cause by
which such species change has occurred over h