Editing Neural Darwinism (section)

== Completing Darwin's program – the problems of evolutionary and developmental morphology ==

In ''Topobiology'', Edelman reflects upon Darwin's search for the connections between morphology and embryology in his [[Natural selection|theory of natural selection]]. He identifies four unresolved problems in the development and evolution of morphology that Darwin thought important:{{sfn|Edelman|1988|p=45}}

* Explaining the finite number of body plans manifested since the [[Precambrian]].
* Explaining large-scale morphological changes over relatively short periods of geological time.
* Understanding body size and the basis of [[allometry]].
* How adaptive fitness can explain selection that leads to emergence of complex body structures.

Later, In ''Bright Air, Brilliant Fire'', Edelman describes what he calls Darwin's Program for obtaining a complete understanding of the rules of behavior and form in evolutionary biology.{{sfn|Edelman|1992|loc=Chapter 5 Morphology and Mind: Completing Darwin's Program}}  He identifies four necessary requirements:

*An account of the effects of heredity on behavior – and behavior, on heredity.
*An account of how selection influences behavior – and, how behavior influences selection.
*An account of how behavior is enabled and constrained by morphology.
*An account of how morphogenesis occurs in development and evolution.

It is important to notice that these requirements are not directly stated in terms of genes, but heredity instead. This is understandable considering that Darwin himself appears to not be directly aware of the importance [[Mendelian genetics]]. Things had changed by the early 1900s, the [[Neodarwinian synthesis]] had unified the population biology of Mendelian inheritance with Darwinian natural selection. By the 1940s, the theories had been shown to be mutually consistent and coherent with paleontology and comparative morphology. The theory came to be known as the ''modern synthesis'' on the basis of the title of the 1942 book ''Evolution: The Modern Synthesis'' by [[Julian Huxley]].{{sfn|Huxley|1942}}

The [[Modern synthesis (20th century)|modern synthesis]] really took off with the discovery of the structural basis of heredity in the form of DNA. The modern synthesis was greatly accelerated and expanded with the rise of the genomic sciences, molecular biology, as well as, advances in computational techniques and the power to model population dynamics. But, for evolutionary-developmental biologists, there was something very important missing... – and, that was the incorporation of one of the founding branches of biology, embryology. A clear understanding of the pathway from [[Germ cell|germ]] to [[zygote]] to [[embryo]] to juvenile and adult was the missing component of the synthesis. Edelman, and his team, were positioned in time and space to fully capitalize on these technical developments and scientific challenges – as his research progressed deeper and deeper into the cellular and molecular underpinnings of the neurophysiological aspects of behavior and cognition from a Darwinian perspective.

Edelman reinterprets the goals of "Darwin's program" in terms of the modern understanding about genes, molecular biology, and other sciences that weren't available to Darwin. One of his goals is reconciling the relationships between genes in a population (genome) which lie in the germ line (sperm, egg, and fertilized egg); and the individuals in a population who develop degenerate phenotypes (soma) as they transform from an embryo into an adult who will eventually procreate if adaptive. Selection acts on phenotypes (soma), but evolution occurs within the species genome (germ).

Edelman follows the work of the highly influential American geneticist and evolutionary biologist [[Richard Lewontin]] (March 29, 1929 – July 4, 2021), drawing particular inspiration from his 1974 book, ''[[The Genetic Basis of Evolutionary Change]]''.{{sfn|Lewontin|1974}} Edelman, like Lewontin, seeks a complete description of the transformations (T) that take us from:{{sfn|Edelman|1988|p=45-47}}

* Genome-germ (zygotes) – the paternal and maternal gene contributions are recombined in the fertilized egg, along with the maternal endowment of proteins, and mRNAs, and other developmental components, but the individuals newly formed diploid genetic complement is not in control of the zygote yet; it needs to be activated, or bootstrapped, into the zygotes ongoing maternally-inherited metabolism and physiology. Shortly after recombination the zygote proceeds through transformation (T1) to the point where genetic control of the zygote has been handed off to the individual,
* Phenotype-soma (embryo) – the embryo, which transforms (T2) according to the rules that govern the relationship between the genes, cellular behavior, and the epigenetic contingencies of nature, into
* Phenotype-soma (adult) – an adult, who procreates (T3) with another individual to bring together a new genetic recombination by each introducing a gamete in the form of 
* Genome-germ (gametes) – sperm and egg, which contain the haploid genetic contribution of each parent which is transformed (T4)...
* Genome-germ (zygotes) -into a diploid set genes in a fertilized egg, soon to be a newly individual zygote .

Lewontin's exploration of these transformations between genomic and phenotypic spaces was in terms of key selection pressures that sculpt the organism over geological evolutionary time scales; but, Edelmans approach is more mechanical, and in the here and now – focusing on the genetically constrained mechano-chemistry of the selection processes that guide epigenetic behaviors on the part of cells within the embryo and adult over developmental time.