The central concept of natural selection is the evolutionary fitness of an organism. Fitness is measured by an organism’s ability to survive and reproduce, which determines the size of its genetic contribution to the next generation.

The best definition of evolutionary fitness is. survival and reproduction relative to other members of the population; An adaptation is a trait of an organism that increases. its fitness, its ability to survive and replicate, in frequency in a population over many generations.

Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it. A genotype’s fitness includes its ability to survive, find a mate, produce offspring — and ultimately leave its genes in the next generation.

Evolution is a process that results in changes in the genetic material of a population over time. Evolution reflects the adaptations of organisms to their changing environments and can result in altered genes, novel traits, and new species.

The theory of evolution has three basic parts: 1) it is possible for an organism’s DNA to change or mutate; 2) the change is harmful, beneficial, or neutral; and 3) after a long period of time, the mutations cause new species to form. Modern evolution theory recognizes that evolution does not always mean progress.

What is evolution? The basic idea of biological evolution is that populations and species of organisms change over time. Darwin also suggested a mechanism for evolution: natural selection, in which heritable traits that help organisms survive and reproduce become more common in a population over time.

Speciation can be driven by evolution, which is a process that results in the accumulation of many small genetic changes called mutations in a population over a long period of time. Natural selection can result in organisms that are more likely to survive and reproduce and may eventually lead to speciation.

Classically, speciation has been observed as a three-stage process:

• Isolation of populations.
• Divergence in traits of separated populations (e.g. mating system or habitat use).
• Reproductive isolation of populations that maintains isolation when populations come into contact again (secondary contact).