A rational synthesis of ToE (Darwinian ToE in a Nutshell)

Monday, October 13, 2008, 1:41 PM

Charles Darwin, his Galapagos and his Beagle

Let's define what we mean (explicitly or implicitly) when we are talking "evolution" that would be "true" or "un-true". These are the three main "ingredients", straight from Darwin's The Origin of Species.
i. All live forms derive from an elementary life form, by means of the two following fundamental "mechanisms.

ii. Non-oriented Variation (as Darwin calls it) or, as we normally refer to it nowadays, Random Mutation.

iii. Mutations express themselves in such a way that only the "advantageous" ones are "passed on" by Natural Selection.

Let's see what Wikipedia says (we could get more authoritative sources, but for the present purpose it is more than sufficient).

At the entry Evolution, wikipedia distinguishes between the different sources of Variation (of the phenotype, of which the main part results from results changes in the genotype) on one side, and the different Mechanisms of (statistically) stable modification of the genotype (viz. the genetic constitution of a cell, an organism, or an individual, i.e. the specific allele makeup of the individual of a species), on the other side.

V. Looking more in detail at Variation, Wikipedia identified three modalities, "[a] random mutations in genetic material, (viz., except for viruses, DNA) [b] migration between populations (gene flow), and [c] sexual reproduction.

[a] Mutations are random "changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication."

[b.] gene flow through migration may introduce a change in the allele makeup of the population affected but the allele makeup of the species as a whole does not change, at most it can get diversified in variants (or races) with more or less marked morphological differences.

[c] sexual reproduction is, essentially, a "reshuffling" of genes, which does not add new information to the gene pool (like the reshuffling of a deck of cards does not change the "information contents" of the deck itself)

So, in conclusion, the only modality of Variation that introduces "novelty" in the genotype of a a species is Random Mutation. We can express it as:

V = RM ("The essential process of Variation, that introduces new information, is Random Mutation)

M. Looking more in detail at the different Mechanisms of modification of the genotype, Wikipedia identified three modalities: [d.] Natural selection, [e.] Genetic drift, and (again) [f.] Gene flow.

[d.] Natural selection is "the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population."

[e.] Genetic drift is "the change in allele frequency from one generation to the next that occurs because alleles in offspring are a random sample of those in the parents, as well as from the role that chance plays in determining whether a given individual will survive and reproduce." So, in synthesis, we may say that, "when selective forces are absent or relatively weak, allele frequencies tend to "drift" upward or downward randomly".

[f.] Gene flow is, again, "the exchange of genes between populations, which are usually [viz. apart from interspecific hybrids] of the same species". As already said, the allele makeup of the population affected may change, but the allele makeup of the species as a whole does not change.

So, in conclusion, the only Mechanism that may significantly alter the genotype of a species, in its interaction with environment, is Natural Selection. We can express it as:

M = NS ("The essential Mechanism that alters the genotype of a species is Natural Selection")