Control Systems in the Living World - Building the Most Complex Structure on Earth - page 7

stage, when only one organ system, the nervous system, is operational. At this early
embryonic stage, when the maternal epigenetic information provided to the embryo
via gametes is exhausted, the CNS is already capable of stepwise computation of the
epigenetic information necessary for the development of the adult metazoan supra-
cellular structures.
The capability of living systems to reproduce their kind leads to two other proper-
ties of the living systems: evolvability and growth.
Evolvability
This is a relatively new biological concept, and its definition depends on the ques-
tion addressed ( Pigliucci, 2008 ). In this context, evolvability is the ability of living
organisms to adapt their phenotype by changes in developmental pathways. Since
evolutionary changes occur in the process of development, the evolution and evolv-
ability of living systems is related to, and is enabled by, the phenomenon of biologi-
cal reproduction. Evolvability is thought to evolve ( Kirschner and Gerhart, 1998 ), as
is clearly indicated by evidence of the acceleration of the rate of evolution.
Genetic changes are too rare and overwhelmingly deleterious to account for the
huge diversity of forms in the living world. The prevailing idea that changes in genes
are necessary for the evolution of living systems is challenged by numerous biologi-
cal phenomena. The concept of the phenotype as a result of the interaction of genes
with the environment fails to explain how, in concrete terms, a change in a gene or
DNA can produce an adaptive morphological change . I emphasize the word adap-
tive because it is well known that mutations in genes can lead to phenotypic changes
at the molecular level; that is, deleterious changes sensu Archibald Garrod's (1857-
1936) “inborn errors of metabolism.” Genome sequencing of various species of uni-
cellular and multicellular organisms, conservation of the genetic toolkit, biological
phenomena such as developmental plasticity (intragenerational developmental plas-
ticity and especially transgenerational plasticity), reversion of ancestral morphologi-
cal characters, metamorphosis in invertebrates and vertebrates, cell differentiation,
loss of morphological characters, etc., suggest that it is not changes in genes or
DNA, but epigenetically determined changes in patterns of gene expression in the
process of individual development that may be responsible for evolution of structure
and morphology.
Growth
In unicellular organisms, growth is a stage in the process of their reproduction. It
consists of a stepwise and ordered increase in the size of the cytoplasm, including
the increase in the number (e.g., ribosomes mitochondria) or duplication of orga-
nelles, (chromosomes, centrosomes, cell nuclei, etc.). In multicellular organisms, as
the founders of the cell theory determined almost two centuries ago, growth consists
of the growth of the number of cells in the process of development, comprising pre-
phylotypic development, histogenesis, and organogenesis.