Darwin's Theory of Evolution

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Darwin's Theory of Evolution

Selection

The process where favourable and unfavourable traits are determined that allows species to evolve and develop beneficial mutations.

Reproduction

The production of offspring - a required step for new species to be produced.

Selection of different traits which occurs naturally:

Natural Selection

Sexual Selection

Selection occurs within the species. One sex is chosen by the other to mate with and competes with members of the same sex for access to members of the opposite sex.

Selection against extremes on both ends favouring the average trait:

Stabilizing Selection

Selection against average traits favouring extremes on either end:

Disruptive Selection

Selection against one extreme favouring another extreme:

Directional Selection

Humans choose which traits are favourable and unfavourable:

Artificial Selection

Ex. Dog breeding

Genes

Carries information that determines certain traits. Through reproduction, genetic information are passed on to offspring.

Alteration of genes:

Mutations

During natural selection, beneficial mutations will make reproduction easier so they will be passed on to later generations more.

Vestigial Features

Components of species no longer serve a purpose due to mutations making their function outdated. Serves as evidence of evolution.

Speciation

The evolutionary process that allows species to evolve into distinct species.

Models of speciation:

Sympatric Speciation

Two populations in the same location evolve differently preventing interbreeding and leading to new species.

Allopatric Speciation

Two populations become geographically isolated leading to new species.

Evolutionary change without selection:

Bottleneck Effect

A chance event causing large population reduction.

Founder Effect

A few individuals of a similar allele frequency from a population act as colonizers creating a new population.

Biological Species

A group of organisms which can breed and produce fertile offspring with only each other

Reproductive Isolation

Mechanisms that prevent different species from mating and producing fertile offspring.

Isolation occurring after the formation of a zygote:

Postzygotic Isolation

Hybrid Infertility

Hybrids are able to live to adulthood but are sterile.

Examples:

Mule

Liger

Hybrid Inviability

Hybrids die off early in development.

Zygote Mortality

Zygotes do not develop to maturity.

Isolation occurring before the formation of a zygote:

Prezygotic Isolation

Gamete Isolation

Sperm and egg of different species aren't able to correctly interact with each other to reproduce.

Mechanical Isolation

Species are unable to mate because their reproductive systems are incompatible.

Behavior Isolation

Species are unable to breed due to having different mating rituals.

Temporal Isolation

Species are unable to breed due to having different breeding seasons.

Habitat Isolation

Similar species are unable to breed because they've adapted to different habitats.

Ecological Isolation

Species are unable to breed due to geographic isolation.

Patterns in Evolution

Adaptive Radiation

Many species developing from a single ancestor due to access to different environments with different pressures:

Biogeography

The study of the distribution of species in certain geographic locations.

An example of biogeography and adaptive radiation:

Galapagos Islands

Houses multiple islands with different pressures which were accessible by the finches. Darwin observed how from a single ancestor, finches were able to evolve into several different species whose traits were developed based on each of the island's certain pressures.

Observed during:

Voyage of the Beagle

Different species evolving as a response to each other:

Co-evolution

Can be caused by symbiotic relationships where:

One organism benefits, the other isn't affected:

Commensalism

One organism benefits, the other receives a negative effect:

Antagonism

Both organisms benefit:

Mutualism

Geographically isolated organism develop similar phenotypes based on similar pressures:

Convergent Evolution

Analogous Features

The different organisms develop Analogous features - similar features which serve a similar purpose across different species.

Different organisms in a same group develop differently leading to new species:

Divergent Evolution

These organisms develop:

Homologous Features

Common ancestors develop features that are similarly structured but functionally different.

Notable Figures

Developed our modern theory for evolution:

Charles Darwin

Acted as Darwin's correspondent for geology:

Charles Lyell

Fossil Record

Geology and the Fossil Record contributed to Darwin's understanding of evolution and the origin of species

Developed a theory of evolution involving a constant growth pattern from simple --> complex:

Jean Lamarck

Economist who also studied population growth:

Thomas Malthus

His work helped Darwin understand population growth and applied this knowledge to different species