Evolutionary Theories: Neutral, Punctuated Equilibrium & Population Genetics

Posted on Apr 2, 2025 in Biology

Evolutionary Theories and Population Genetics

Genetic recombination during meiosis results in offspring variations. These variations occur randomly and are pre-adaptive.

Hardy-Weinberg Principle

Hardy and Weinberg demonstrated that in a population (k) + tax, individuals die and lose characteristics, but the population remains. The genetic stocks are all individuals with the ability to reproduce sexually with each other.

Evolutionary Forces

Fisher, Haldane, and Wright demonstrated that changes in gene frequency (k) can induce evolution. These forces include natural selection, mutations, and migration.

Speciation

For two populations (XK) to evolve differently and give rise to two species, they must remain isolated from one another.

Neutral Theory of Molecular Evolution

Neutral Theory: Kimura proposed the neutral theory of evolution in 1968. It posits that most molecular mutations are neither favorable nor unfavorable; they are neutral. Natural selection does not affect most molecular evolutionary changes, meaning these changes are not adaptive.

Punctuated Equilibrium Theory

The traditional view observes gradual changes, which have successively more noticeable turns and bumps, called the model of phyletic gradualism (k te carcho + tax):

  1. All species form a single evolutionary line from the ancestor.
  2. The transformation is slow and continuous.
  3. Transformation occurs throughout the population.

Punctuated equilibrium represents the sudden disappearance of existing species and the appearance of others. Eldredge and Gould, in 1972, explained the theory of punctuated equilibrium. It is based on a small population of ancestral species that was isolated and evolved differently until a new species emerged. This theory differs from the model of phyletic gradualism in that:

  1. The species is not formed by a single line but by two or more lines from an ancestral species.
  2. It alternates stages in the transformation of slow or no change (“stasis”) with periods of very rapid transformation (“speciation”).
  3. The transformation to the new species does not occur throughout the early area but in a small, isolated subpopulation.

Population Genetics

Neo-Darwinism brought essential concepts to explain the mechanism of evolution:

  1. Population genetics with gene and genotypic frequencies.
  2. Factors that alter gene frequencies: natural selection, mutation, migration.
  3. Geographical isolation of subpopulations.

Population Genetics and Gene Frequency

A population is the set of individuals of the same species inhabiting the same place and interbreeding, sharing a common set of genes and a common genetic background.

  1. Genotypic frequencies are the frequencies of each genotype.
  2. Gene frequencies are the frequencies of each allele for each character.

The Law of Hardy-Weinberg

The Law of Hardy-Weinberg, studied in 1908, states that in a population of organisms with sexual reproduction where individuals cross at random and there is no mutation, migration, or genetic drift, gene and genotypic frequencies remain constant from generation to generation.

Demonstration of the Law

Consider a population under Hardy-Weinberg conditions where a particular locus has two alleles. The alleles are distributed among the gametes according to their gene frequencies. This law is affected by mutations, migrations, and natural selection.

Mutations

Mutations are unexpected and random changes in genetic information. They can lead to the appearance of other alleles. Preadaptations are not necessarily beneficial in all directions. Wholesale mutations, also known as recurrent mutations, have an important role in evolution.

Migration

Migration involves the arrival of individuals from other populations (immigrants) or the departure of individuals (emigrants).