D4.1 Natural Selection

Natural selection is the process in which individuals with advantageous inherited traits survive and reproduce more successfully than others. Over time, these beneficial traits become more common in the population, causing evolution.

Natural selection is the main mechanism responsible for evolutionary change and biodiversity. It explains how species adapt to their environments over generations.

Evolution is the change in inherited characteristics (allele frequencies) of a population over generations.

Darwin understood that: * Individuals vary in phenotype * Some traits improve survival and reproduction * Better-adapted individuals leave more offspring * Traits are inherited * Populations gradually change over time He did not know how genes, DNA, or mutations worked

The environment interacts with observable traits (phenotypes), not directly with genes. However, because phenotypes are genetically controlled, selection indirectly changes genotype and allele frequencies.

Fitness is an organism’s reproductive success — its ability to survive and produce fertile offspring that pass alleles to the next generation.

Charles Darwin and Alfred Russel Wallace independently proposed the theory of evolution by natural selection.

Darwin used: Observations from the Beagle voyage Species variation in the Galápagos Islands Fossils Geographic distribution of organisms Adaptations of organisms

It replaced the previous belief that traits acquired during life were inherited (Lamarckism) with the idea that inherited variations already present in populations are passed to offspring.

Darwin observed extreme insect adaptations and concluded that: * Different environments create different selection pressures * Organisms evolve traits suited to specific ecological niches * Adaptations increase survival and reproductive success

Darwin predicted the existence of a moth with a very long proboscis capable of reaching nectar deep inside a 30 cm orchid nectary. The moth was discovered decades later.

• Overproduction of offspring • Variation within populations • Competition for limited resources • Inheritance of advantageous traits

More offspring are produced than can survive, creating competition for limited resources.

Variation arises from: * Mutation * Sexual reproduction * Crossing over * Independent assortment * Random fertilization

Mutation creates new alleles and therefore new genetic variation, which natural selection can act upon.

Sexual reproduction produces unique allele combinations through: * Crossing over * Independent assortment * Random fertilization

Competition creates selection pressure because individuals must compete for: * Food * Territory * Mates * Shelter Those with advantageous traits survive and reproduce more successfully.

Traits must be genetically inherited for them to be passed to offspring and increase in frequency in future generations.

• Mutations produced red coloration and spots • Birds avoided red ladybirds • Brown ladybirds were eaten more often • Red ladybirds survived and reproduced more • Red alleles increased in frequency

Without variation, all individuals would have equal survival chances and selection would be random rather than directional.

Abiotic factors are non-living environmental conditions that affect organisms. Examples: * Temperature * Water availability * pH * Light intensity * Salinity * Soil composition * Humidity

Individuals with phenotypes better suited to abiotic conditions survive and reproduce more successfully, increasing the frequency of their alleles.

The tolerance range is the range of environmental conditions in which an organism can survive and reproduce.

Rising temperatures favor individuals with heat-tolerant phenotypes. These individuals survive and reproduce more, shifting allele frequencies over time.