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et al. 2008). Although some role for the environment in directing
heritable traits clearly exists (Jablonka and Lamb 2008), the history of
how this role has been presented has contributed to maintaining confu-
sion, controversy, and even skepticism about the soft (reset at meiosis),
epigenetic (non-DNA) nature of inheritance (Richards 2006).
B. The Role of the Environment in Evolution
The pre-Darwinian work of Lamarck proposed an all-encompassing
environment-directed (active) mechanism to explain polymorphic life
that was essentially inconsistent with the passive concept of natural
selection proposed by Darwin. Therefore, after Darwin, and especially
after Mendel
s theory became greatly
discredited. However, the discovery and clear establishment of the
ability of some epigenetic traits to be transgenerational and also be
directed by the environment seemed to somewhat resonate with
Lamarck
'
s work was understood, Lamarck
'
s view (Kakutani 2002; Richards 2006; Youngson and White-
law 2008). To help understand the possible role of environment-
directed phenotype change in the context of Darwinian evolution, it
is instructive to recall and emphasize that an important part of the
discrediting of Lamarck
'
'
'
s paradox that
explained that traits had to be directed by the environment in the
germ cells in order to pass through sexual generations. Since germ cells
are often established and
s view arose from Weismann
fixed in a strict cell lineage rapidly after
gamete fusion in many organisms, especially in mammals, any direct
in
uence of the environment has to occur in a very narrow window in
the life cycle to have a reasonable probability to be transgenerational.
This should greatly limit any possibility for the environment to direct
heritable changes.
C. Transgenerational Epigenetics
Environmental effects on heredity have been widely observed and
sometimes referred to as provenance effects (Lacaze 1978; Burczyk
and Giertych 1991; Shutyaev and Giertych 1997, 2000; Giertych
2007) or as maternal environmental effects, and many of them have
been demonstrated to be transgenerational (Donohue and Schmitt 1998;
Martienssen and Colot 2001; Tani et al. 2005; Bond and Finnegan 2007;
Youngson and Whitelaw 2008). The epigenetic mechanism(s) responsi-
ble for the transgenerational memory of environmental episodes is not
precisely known, but DNA methylation and chromatin modi
cation
have been revealed to be responsible in some cases (Youngson and
