Darwin's Theory of Evolution

Notable Figures

Economist who also studied population growth:

Thomas Malthus

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

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

Jean Lamarck

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 our modern theory for evolution:

Charles Darwin

Patterns in Evolution

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.

Geographically isolated organism develop similar phenotypes based on similar pressures:

Convergent Evolution

These organisms develop:

Analogous Features

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

Different species evolving as a response to each other:

Co-evolution

Can be caused by symbiotic relationships where:

Both organisms benefit:

Mutualism

One organism benefits, the other receives a negative effect:

Antagonism

One organism benefits, the other isn't affected:

Commensalism

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

Species A migrates from the mainland to the first island.Isolated from the mainland, species A evolves to species B.Species B migrates to the second island.Species B evolves in species C.Species C recolonizes the first islands, unable to reproduce with species B.Species C migrates to the third island.Species C evolves into species D.Species D migrates to the first and second islands.Species D evolves to species E.

Speciation

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

Reproductive Isolation

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

Isolation occurring before the formation of a zygote:

Prezygotic Isolation

Ecological Isolation

Species are unable to breed due to geographic isolation.

Habitat Isolation

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

Temporal Isolation

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

Behavior Isolation

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

Mechanical Isolation

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

Gamete Isolation

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

Isolation occurring after the formation of a zygote:

Postzygotic Isolation

Zygote Mortality

Zygotes do not develop to maturity.

Hybrid Inviability

Hybrids die off early in development.

Hybrid Infertility

Hybrids are able to live to adulthood but are sterile.

Examples:

Liger

Mule

Biological Species

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

Some species may express similar phenotypes, but if they're unable to mate and produce fertile offspring they're not considered biological species.

Evolutionary change without selection:

Founder Effect

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

Bottleneck Effect

A chance event causing large population reduction.

Models of speciation:

Allopatric Speciation

Two populations become geographically isolated leading to new species.

Sympatric Speciation

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

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.

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.

Humans choose which traits are favourable and unfavourable:

Artificial Selection

Ex. Dog breeding

Selection of different traits which occurs naturally:

Natural Selection

Selection against one extreme favouring another extreme:

Directional Selection

Selection against average traits favouring extremes on either end:

Disruptive Selection

Selection against extremes on both ends favouring the average trait:

Stabilizing 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.