Rise of the Animal Kingdom and Epigenetic Mechanisms of Evolution - Building the Most Complex Structure on Earth - page 288

Human speech is one of the most complex neural and motoric behaviors that we
are aware of.
While it is not impossible for the FOXP2 gene (or other genes) to be involved
in the evolution of speech, it would be a gross simplification to consider speech a
genetic phenomenon related to the presence or absence of a gene or changes in a
gene or its regulatory sequences. Human speech is a primarily epigenetic phenom-
enon involving complex and still little understood neural processing, cognitive, and
motor functions; only the last element in the speech circuitry, the regulation of air
flow through the larynx to produce the sound is an intricate process involving the
actions and harmonizations of actions of numerous nerves, muscles, and ligaments
of the larynx and neighboring regions and organs. This process cannot be considered
a genetic phenomenon, by any stretch of imagination.
The mechanism of gene recruitment was another sine qua non for evolution of
animals in the Cambrian period and even earlier. Understanding that mechanism is a
critical requirement for the development of the theory of evolution. Again, the only
available approach for understanding how animals that lived over half a billion years
ago recruited their genes is to study the phenomenon in their extant descendants.
We know of animals where the gene recruitment may be subject to experimental
induction. For example, when all the female species of Daphnia magna are reared
under unfavorable stressful conditions (e.g., scarce food and crowding), they pro-
duce sexually reproducing (male and female) offspring. The developmental mech-
anism of this major phenotype is known: the processing of environmental data
generates the information necessary for activating a new signal cascade starting in
the brain (X-organ/sinus gland complex) that stimulates/inhibits production of the
methyl farnesoate by the mandibular organ and inhibition/expression of the methyl
farnesoate receptor, leading to the expression/suppression of genes for producing
mictic (male and female) offspring ( Figure 5.19 ).
In the above and a number of other cases, the recruitment of genes in new path-
ways, signal cascades, or GRNs starts with chemical signals released by the mother's
brain as a result of processing of the various environmental stimuli. But if mech-
anisms of gene recruitment, which are indispensable for evolution of the animal
world, operate in these extant lower invertebrates, why doubt that they were opera-
tive at the Cambrian ( Cabej, 2011 ). We do not know how old these neural mecha-
nisms of gene recruitment are, but there is no reason to believe that they evolved
only in our time. If the processes of development really do reflect the evolutionary
history of species, as the postulate of the phylogenetic actualism posits, the neural
mechanisms of similar gene recruitment evolved since the dawn of animal evolution,
at least at the beginning of the Cambrian explosion.
Leaving evo-devo knowledge and theoretical arguments aside, we delve into
the evolutionary history of the recruitment of specific genes. Salamanders of the
Plethodontid family have two main pheromone genes, sodefrin precursor-like factor
(SDF) and plethodontid receptivity factor (PRF). Between 50 and 100 million years
ago, they recruited SPF for regulating male sexual behavior and female receptivity.
The red-legged salamander, Plethodon shermani , has both of those genes, but about
27 million years ago it recruited PRF to replace SPF as regulator of the male sexual