Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 65

the receiver reflects each other ( Griffiths, 2000 ). However, the extrapolation from
communications theory to biological information may not be warranted. The above
propositions refute any idea of the primacy of DNA over phenotypic structures as a
carrier of biological information and of the direction of the flow of information from
DNA to phenotype.
It is curious to observe that as a reaction to the increasing evidence of the role
of extragenetic factors in inheritance, many biologists adhere to a dichotomous
concept of replicators and interactors, a view that gives genes and DNA a predomi-
nant role in inheritance, above and beyond other causal factors in development.
According to this view, the genome has the monopoly of biological information,
and biological entities are primarily little more than vehicles contributing to the
immortality of replicators.
In response, the representatives of a new theoretico-philosophical trend known as
the developmental systems theory ( DST ) came up with the “parity thesis,” positing
that all the elements (genetic and nongenetic) that interact during the developmental
process are “parental resources.” Accordingly, what really exist and determine the
developmental and replication cycles of living systems are not replicators and inter-
actors, but “developmental resources” ( Griffiths and Gray, 1994 ). The sum of all
developmental resources (i.e., of the elements involved in the developmental process)
represent the developmental system. DST thus extended the biological contrivances
of inheritance to include extragenetic elements. Developmental processes, according
to this view, are cyclic series of events in which each cycle (developmental process)
is a “causal consequence” of the preceding one ( Griffiths and Gray, 1997 ). Not only
the genome but also the other elements in the developmental system and developmen-
tal interactions are replicated ( Griffiths and Gray, 1994 ). Indeed, DNA is not the only
known biological structure that can copy itself; centrosomes and centrioles have their
own self-replication machinery, and no DNA is involved in their replication ( Balczon
et al., 1995; Rattner and Phillips, 1973 ). The already classic experiments of Beisson
and Sonneborn (1965 ) have shown that the Paramecium cortex reproduces itself
exactly, without involving the genome.
However, Shea (2011 ) conditions the qualification of the developmental resources
as carriers of inherited representations with whether they have the metafunction of
“transmitting selected phenotypes down the generations.” Nevertheless, he prudently
admits that if his concept of the metafunction of the DNA is wrong, then “another
account of inherited representation would be needed.” In order for a developmen-
tal resource to be thought as part of an inheritance system, it should have semantic
information in the form of “instructions” for building a structure. By denying this
possibility for other “developmental resources,” he ignores the unambiguous empiri-
cal evidence on transgenerational developmental plasticity. Recall that even according
to his own criterion, epigenetic variations in the offspring have to be “carried down
the generations,” and transgenerational developmental plasticity falls in the category
of what he calls “inherited representations.” Transgenerational developmental plasticity
(discussed further in Chapter 5) arises epigenetically and involves no changes in genes.
Focusing on the well-known fact that ostriches prenatally form calluses on the skin
of parts of their body that come in contact with the ground (i.e., breast, pubis, and