3. Evolution

• Theory of evolution of the species

• Theory of a common descent

• Theory of the multiplication of species

• Theory of gradualism

• Theory of natural selection

• Theory of sexual selection

The world is constantly changing, it isn’t recently created nor has a repetitive cycle. Therefore organisms must transform in time.

Every group of organism descended from a common ancestor, all species including animals, plants and micro-organisms go back to a single origin of life.

New species arise by the splitting of existing species into two or more new ones. This can happen when populations get separated or when they diverge over time, eventually becoming so different that they can no longer interbreed.

Evolutionary change happens slowly and continously through many small changes in a population over long periods of time. These tiny changes add up, and eventually the population becomes so different that it forms a new species.

The theory was proposed by Charles Darwin and explains that species change over time because individuals with advantageous traits are more likely to survive and reproduce, passing those beneficial characteristics to their offspring.

Sexual selection explains traits that evolve because they improve mating success.

There are two types:

• Intrasexual selection: competition within one sex (usually males) for access to mates, e.g., fighting, strength, or weapons like antlers.

• Intersexual selection: mate choose between sexes (usually females choosing males), favouring traits like bright colours, courtship displays, or songs.

Together, these processes increase the chances of reproducing, so the successful traits become more common over generations.

• Natural selection: Individuals with advantageous traits survive and reproduce more, causing those traits to become more common.

• Genetic Drift: Random changes in allele frequencies, especially in small populations (e.g., by chance events or bottlenecks).

• Migration (Gene Flow): Movement of genes between populations through migration, which introduces new alleles and reduces differences between populations.

• Mutation: random changes in DNA that create new gentic variants. Mutation is the original source of all new genetic information.

• Mutations create new alleles

• Gene Flow adds variation by introducing alleles from other populations

• Recombination during sexual reproduction shuffles genes (crossing over + independent assortment.

Macroevolution describes large-scale evolutionary changes above the species level (formation of new species). It is defined as the change between species, not within species (microevolution).

Evidence comes from fossil records, comparative anatomy, molecular similarities, all of which show patterns of common ancestry and long-term evolutionary changes.

Microevolution refers to small-scale genetic changes within a population over short time periods, such as changes in allele frequencies.

Driving molecular mechanisms are:

• Mutation (creates new genetic variants)

• Migration (brings new alleles into a population)

• Genetic drift (random changes, especially in small populations)

• Natural selection (different survival and reproduction of variants)

Any change in the DNA.

• Insertion mutation

• Deletion mutation

• Nonsense mutation

• Missense mutation

• Frameshift mutation

• Repeat expansion mutation

A single nucleotide is inserted into the original DNA code, which results in an incorrect amino acid sequence. This can produce a malfunctioning protein and disrupt the gene’s function.

A single nucleotide is deleted from the original DNA code, which may shorten or completely alter the gene.

A normal codon is changed into a stop codon, causing the protein to be cut off too early.

A single nucleotide is replaced, which results in a different amino acid in the protein.

An insertion or deletion shifts the reading frame, changing all downstream amino acids.

A short DNA sequence is repeated too many times, disrupting gene function.

For example a repeated trinucleotide (CAG) adds a string of glutamines (Gin) to the protein.

Gene duplication is the making of a working gene, so the organism ends up with two copies instead of one.

Mechanism:

One common mechanism is unequal crossing-over, where chromosomes incorrectly swap DNA during reproduction, leaving one chromosome with an extra gene.

Another way is retrotransposition, where a gene’s messenger RNA (mRNA) is copied back into DNA an reinserted somewhere else, making a special copy called a retrogene.

Significance:

Gene duplication is highly important in evolution because the original gene keeps doing its jobs, but the new copy is free to mutate.This allows the duplicate to potentially develop a totally new and beneficial function, leading to the creation of diverse gene families and driving the evolution of new traits and complexity in living things.

Mechanism:

An entire set of chromosomes is duplicated, often due to errors in meiosis or cell division. The organism ends up with extra full copies of its genome.

Significance:

Genome duplications provide a huge amount of new genetic material (massive gene duplication), enabling major evolutionary innovations. They are especially common in plants, where they often leas to new species.

Two particularly important Mechanisms:

• Chromosome Inversion: A segment of a chromosome breaks, flips 180°, and reattaches. This changes the gene order and can reduce recombination in the inverted region.

• Genome Duplication: An entire set of chromosomes is duplicated (polyploidy), usually due to errors in meiosis or cell division. This results in organisms with extra whole genome copies.

Significance for Evolution:

Chromosome mutations create large-scale genetic changes that can alter gene expression, preserve advantageous gene combinations, and provide new genetic material.

They increase genetic diversity, support adaptation, and can contribute to the formation of new species.