IB Biology: Evolution and Speciation Key Concepts and Evidence

Evolution

Change in the heritable characteristics of a population over generations

Homologous Structures

Structures that are similar in different species due to common ancestry.

Selective Breeding

The process by which humans breed plants and animals for particular genetic traits.

Common Ancestor

An ancestral species from which multiple species have evolved.

Pentadactyl Limb

A limb structure with five digits found in many vertebrates, indicating common ancestry.

Population

A group of individuals of the same species living in a specific area.

Convergent Evolution

The process by which unrelated organisms develop similar traits due to similar environmental pressures.

Analogous Structures

Structures that serve similar functions in different species but do not share a common ancestry.

Extinction

The end of an organism or a group of organisms, typically due to environmental changes or loss of habitat.

Reproductive Isolation

A mechanism that prevents species from mating and producing viable offspring.

Geographical Isolation

A form of reproductive isolation where species are separated by physical barriers.

Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins

Sequence data gives powerful evidence of common ancestry.

Evidence for evolution from selective breeding of domesticated animals and crop plants

Demonstrates how human intervention can lead to significant changes in species over time.

Evidence for evolution from homologous structures

Indicates common ancestry through structural similarities in different species.

Speciation by splitting of pre-existing species

Occurs when a population diverges into two or more distinct species.

Roles of reproductive isolation and differential selection in speciation

Reproductive isolation prevents interbreeding, while differential selection drives adaptation and divergence.

Evidence for Evolution

The biomolecules DNA, RNA and proteins provide strong evidence for evolution.

Mutations

Differences in the base sequences of DNA (and therefore RNA and proteins) are the result of mutations.

Mutation Rate

Mutations accumulate gradually over long periods of time at a constant rate.

Closely Related Species

Closely related species have very similar gene and protein sequences, as there will be a small number of mutations because they diverged from a common ancestor.

Selective Breeding of Dogs

Dogs (Canis lupus familiaris) were domesticated from wolves (Canis lupus) 15000 years ago.

Pentadactyl Limbs

Pentadactyl limbs are an example of homologous structures.

Function of Pentadactyl Limbs

The structure of the limb is similar in all species, but has evolved modifications for a variety of purposes such as carrying tools in humans, running in dogs, flying in birds and swimming in whales.

Example of Analogous Structures

Wings of birds, bats and insects are analogous structures, as they have the same function (flight) but do not share a common ancestor.

Geographical Isolation of Apes

The population of the ancestor became geographically isolated into two distinct populations which were separated as the Congo river became wider.

Reproductive Isolation of Apes

The ape populations were reproductively isolated, as members of each population were unable to reproduce with each other.

Differential Selection

The selection pressures were different on the two sides of the Congo river, leading to different traits being selected in the apes.

Sympatric Speciation

The evolution of new species from a single ancestral species while inhabiting the same geographic region.

Allopatric Speciation

The evolution of new species due to geographical isolation.

Behavioural Isolation

Reproductive isolation due to differences in mating behaviors.

Temporal Isolation

Reproductive isolation due to organisms reproducing at different times.

Biodiversity

The variety of life in the world or in a particular habitat or ecosystem.

Niche

The role or function of an organism or species within an ecosystem.

Adaptive Radiation

The diversification of a group of organisms into forms filling different ecological niches.

Hybridization

The process of combining different varieties of organisms to create hybrids.

Prezygotic Barriers

Factors that prevent mating or fertilization between species.

Postzygotic Barriers

Factors that prevent hybrid offspring from developing into viable adults.

Sterile

Incapable of producing offspring.

Hybrid Inviability

A condition where hybrid offspring do not survive to maturity.

Hybrid Infertility

A condition where hybrid offspring are unable to reproduce.

Hybrid Breakdown

A condition where the second generation of hybrids is inviable or sterile.

Polyploidy

The condition of having more than two complete sets of chromosomes.

Triploid

An organism with three sets of chromosomes.

Tetraploid

An organism with four sets of chromosomes.

Cicadas

Different species of cicada have different life cycle lengths: either 13 or 17 years.

Cicada Life Cycle

Cicadas remain as larvae underground during most of their life cycle. At the end of the life cycle the adults emerge, live for a short time above ground and reproduce, then die.

Temporal Isolation in Cicadas

The adult cicadas with a 13 year life cycle will rarely be present at the same time as the cicadas with a 17 year life cycle.

Adaptive Radiation of Darwin's Finches

Darwin's finches evolved by adaptive radiation from a single mainland species which moved into the different niches available on the Galapagos Islands.

Adaptive Radiation Increases Biodiversity

Adaptive radiation and divergent evolution increase the biodiversity of an ecosystem with vacant niches.

Mule

A mule is an example of a sterile hybrid, being the offspring of a male donkey and a female horse.

Barriers to Hybridization

Hybrids are rarely formed between different species due to prezygotic or postzygotic barriers.

Mechanical Isolation

Mechanical isolation occurs when physical differences between organisms prevent sexual intercourse.

Polyploidy Results

Results from non-disjunction, an error during meiosis (while producing gametes).

Immediate Speciation

Polyploidy can produce immediate speciation, as an organism is produced with a different number of chromosomes.

Persicaria maculosa

A tetraploid (4n) plant known for producing bigger fruits.

Uneven Number of Chromosomes

Polyploid plants with an uneven number of sets of chromosomes (3n, 5n, 7n ...) are sterile.

Adaptive radiation

occurs when many similar but distinct species evolve rapidly from a single species →Darwin’s finches