Living and Adapting to Its Own Habitat - Building the Most Complex Structure on Earth - page 223

At a global genomic level, changes between the two phases are observed in 1444
(15.8%) of 9154 genes analyzed ( Burrows et al., 2011 ). Gregarious locusts also show
a higher DNA methylation level in both repetitive and protein-encoding regions
( Robinson et al., 2011 ).
Phase transition is also transmitted to the offspring, but the transgenerational phe-
notypic changes will be dealt with in the following sections.
Transgenerational Developmental Plasticity—Insights
into the Nature of Evolutionary Morphological Change
A basic tenet of the new synthesis is that any evolutionary changes in pheno-
type result from the action of natural selection over mutations in genes/regulatory
sequences or over existing genetic variability. At present the biology has no tools
for telescoping the mechanisms of evolutionary changes that occurred in the past,
but many gene mutations can be related to the evolution of physiological traits at the
molecular level.
The situation is different when it comes to the evolution of morphological, behav-
ioral, and life history traits. Extensive experimental attempts over about 100 years to
produce evolutionary morphological changes through gene mutations have failed in
the sense that they invariably resulted in harmful effects on the animal's fitness and
survival. Being harmful for the organism, such changes would normally be elimi-
nated rather than spread in natural populations.
The century-long empirical failure to relate the evolution of genes to morphologi-
cal, behavioral, and life history traits is not a surprise from the perspective of modern
biology knowledge. As Nijhout (1990) points out, the only thing that genes code for
is the primary structure of proteins. Morphologies do not arise from proteins, but
from specific patterns of spatial arrangement of cells of different types. Almost by
consensus, it is now admitted that cell differentiation, the formation of numerous dif-
ferent types of cells of the same genotype, is an epigenetic process.
The empirical and theoretical failure to explain the evolution of phenotype at a
supramolecular level by changes in genes, along with the new concept of the com-
mon metazoan genetic toolkit of several hundred genes from several dozen gene
families ( Rokas, 2008 ), contributed to the development of a new field of biological
study. This area, known as evolutionary developmental biology or evolution of devel-
opment (evo-devo), intended to look for the sources of evolutionary change in indi-
vidual development.
Chapter 3 showed that the development of the metazoan embryo from the unicel-
lular stage (egg or zygote) to the phylotypic stage is determined by the epigenetic
information in the form of cytoplasmic factors parent(s) provide to the zygote. After
the phylotypic stage, the development of different species depends on the specific
patterns of expression of basically the same genetic toolkit, leading to cell differen-
tiation and organogenesis.