Behavioral Genetics and Animal Science - Genetics and the Behavior of Domestic Animals - page 8

Lamarckism
Jean-Baptiste Lamarck (1744

1829) was a French naturalist remembered for
a theory of inheritance of acquired characteristics, more commonly referred to
as soft inheritance, Lamarckism, or the theory of use/disuse. Lamarck believed
that animals could acquire a certain trait during its life-span and that the
genetic code could be changed. For example, he believed that if a giraffe
throughout its life stretched its neck to reach leaves high in the tree tops,
its neck would become longer and these changes would be passed along to the
offspring. Many of Lamarck's ideas were ridiculed. Today we know that a
giraffe stretching its neck will not make it longer. However, his theory that
genes can be changed during life and the changes can be passed on to
offspring is actually now very credible. Part of Lamarck's argument is actually
supported now by the emerging field of epigenetics. One part of this new
branch of science is based on the proteins (histones) binding to the DNA,
winding it into a small enough shape to fit into the cell ( Probst et al., 2009 ).
Chemicals cause histones to bind either tighter or looser. Certain influences
during life can influence the tightening or loosening of histones, these changes
are then passed on ( Sarma and Reinberg, 2005 ). If a piece of genetic code
is loose, it will be easy to read, if it is tighter, it will not be read. This changes
the expression of the genes and to a large extent explains the difference
between twins at older ages, even when their genes are exactly the same
( Fraga et al., 2005; Poulsen et al., 2007 ). Another epigenetic modification
which serves to regulate gene expression without altering the underlying
DNA sequence is DNA methylation. In simple terms, DNA methylation acts
to “turn on” or “turn off” a gene. The methylation “lock” prevents a section
of DNA code gene from being read and expressed. For example, maternal obe-
sity before and during pregnancy in mice affects the establishment of body
weight regulatory mechanisms in her baby. This is caused by methylation
locks that lock out a section of genetic code. Overweight mothers give birth
to offspring who become even heavier, resulting in amplification of obesity
across generations ( Champagne and Curley, 2009 ).
All of this has little to do with Lamarck, except to support his idea that
individuals could evolve, not just populations as Darwin said. These traits
are then passed on to their offspring. While no biologist believes that organ-
isms can willfully change their physiology in response to their environment
and pass those changes on to their offspring, some evidence suggests that
the environment can make lasting changes to the expression of genes via
epigenetic mechanisms—changes that may be passed on to future genera-
tions ( Crews, 2010 ). Studies in rats show that epigenetics influences maternal
behavior and the effect can be passed on from one generation to the next
( Cameron et al., 2008 ). The offspring of rat mothers who display high levels
of nurturing behavior such as licking and grooming are less anxious and pro-
duce less stress hormones, compared to the offspring of less nurturing
mothers. In turn, the female offspring of nurturing mothers become nurturing