A4.1.1-A4.1.7 Evolution and Speciation

acquired characteristics vs heritable characteristics

acquired characteristics: characteristics of individual organisms that change during lifetime

heritable characteristics: traits inherited by offsprings from parents

evolution

the change in the heritable characteristics of a population

previous theory before evolution

Lamarckism

Lamarckism

inheritance of acquired characteristics

• no mechanism discovered for inheritance of acquired traits

evidence for evolution and natural selection

• structural evidence: the more closely related the species are in morphology, the fewer differences in base sequences

• species develop over time, gradually diverging from a common ancestor as a result of differences in natural selection

• combination of differences → easily accounted for by repeated splitting of ancestral species by evolution

how is selective breeding an evidence for evolution

the considerable changes that have occurred in domesticated animals and crop plants over relatively short periods of time → artificial selection cause rapid evolution → natural selection can cause even larger evolutionary changes to species

homologous structures

• structural similarities

• different functions

• due to common ancestry

pentadactyl limb

limb with five digits (toes or fingers)

parts of pentadactyl limb

• 1 bone (proximal): Humerus (arm) / Femur (leg)

• 2 bones (distal): Radius & Ulna / Tibia & Fibula

• Wrist/ankle bones: Carpals / Tarsals

• Five digits: Metacarpals & Phalanges / Metatarsals & Phalanges

adaptive radiation

• many different groups evolved from a common ancestor

• homologous feature develop in widely different ways to suit the type of locomotion

analogous structures

biological features in different species that perform a similar function but do not share a common evolutionary origin

convergent evolution

• different ancestors

• perform same/similar functions

• become similar

speciation

one species evolving into two

speciation vs extinction

speciation: increase biodiversity and total number of species

extinction: reduce biodiversity and total number of species

talk about speciation

• 2 populations separate

• no interbreeding takes place

• natural selection causes different evolution process

• characteristics of populations diverge

• even if given opportunity to interbreed, they will fail to do so

2 processes required for speciation

• reproductive isolation

• differential selection

interbreeding and speciation

interbreeding: mixes genes, blends traits

speciation: depends on separation of genes

gene pool

genes of a population

geographical separation

physical barriers that are difficult to cross → prevent interbreeding between populations

example of geographical separation

• Lava lizards of the Galapagos archipelago

  • endemic species on islands: only found in a specific geographical area (the islands)

    • a population of species extends its range by migrating to an island

    • speciation takes place

    • thus large number of endemic species on islands

  • one species is present on all the larger islands of the archipelago

  • there are six closely related but different species on six other smaller islands

    • formed by migration to islands, reproductive isolation, divergence due to differential selection

differential selection

• natural selection operating the same way in 2 populations → traits remain the same

• differences in selection → traits gradually become more different

factors causing differential selection

• climate - temperature, rainfall

• predation - different predators / no predators

• competition - resource availability

theory behind bonobos and chimpanzees

(geographically separated by Congo River)

• at some point in history, water level dropped

• chimpanzees travelled to the south

• water level rose

• the second population was subject to different selection pressures

• second population became bonobos

changes in a gene pool during speciation

• gene pool = all genes in a population

• gene pool divides during speciation

• reproductive isolation

• temporal / behavioural / geographical isolation takes place

• gene pool diverge

• allele frequencies change

• natural selection happens differently

• speciation has occurred when differences between populations prevent interbreeding