Variation and Evolution

Variation

Variation is the existence of differences between individuals within a species. It can either be genetic or environmental.
Genetic variation is caused by differences in genes or chromosomes, dictating the organisms’ phenotype such as skin, eyes and hair colour.
Environmental variation is caused by factors that impact an organism’s development. It includes nutrition, temperature, light levels or lifestyle factors.
Continuous variation show a complete range of measurements from one extreme to another within a population such as human height.
Discontinuous variation have distinct classes or categories, such as blood type or sex.

Mutation involves changes in the structure or amount of an organism’s DNA, often resulting in new genetic variability.
Meiosis is a type of cell division that produces four daughter cells. This process introduces genetic variation via independent assortment and crossing over.
Fertilisation also leads to variation because it combines the genetic material of two organisms yielding diverse offspring.

Understanding evolution means acknowledging how species originate, evolve over time, and become extinct.
Natural selection, sometimes referred to as survival of the fittest, describes how better adapted individuals within a population have a higher chance of survival and, consequently, passing on their advantageous traits to their offspring.
Evolutionary adaptation is the process via which a species adapts to its environment over time, driven by natural selection.
Speciation happens when populations evolve to become distinct species. This could occur due to geographic isolation, reproductive isolation or through genetic divergence.

Evolutionary trees, or phylogenetic trees, illustrate the relationships between different species, demonstrating how each species has evolved from a common ancestor.
Each branching point, dubbed a node, on the tree represents a common ancestor from which the species diverged.
Species that share a recent common ancestor and closely related are known as sister groups.
The length of the branches often represents the amount of genetic change, so longer branches show more change.

Paleontology involves studying fossils to understand how species have evolved over time.
Comparative anatomy focuses on comparing the structures of different species to examine their evolutionary relationships, for instance looking at homologous and analogous structures.
Embryological evidence looks at the development of organisms before birth or hatching to find common ancestry.
Molecular biology gives us the ability to compare DNA and protein sequences between species, which is currently the most accurate source of evidence for relationships between species.