Human Evolution and Speciation

A complete vocabulary review covering key definitions, theories, and concepts related to human evolution and speciation from the lecture notes.

Arboreal

Species that mostly inhabit trees rather than the ground.

Australopithecine

Group of extinct bipedal hominins ancestral to H. sapiens. For example, A. anamensis, afarensis, africanus.

Biological evolution

Changes in the genetic information of a population passed down from parent to offspring through many generations.

Bipedalism

Locomotion where most of the motion involves only two legs.

Brachiating

Locomotion of primates that are arboreal, where arms are used to swing from branch to branch. Used by most apes.

Broca area

Part of the brain used in speech production.

Cultural evolution

Evolution where culture, such as clothing, language, music, tool making and religion, is passed on through teaching. Much faster than biological evolution.

Hominid

Family of species that includes apes and humans.

Mitochondrial DNA

Circular DNA found in the mitochondria. Passed down through the maternal line. Does not undergo crossing-over. Has a relatively constant mutation rate and no proofreading. It can be used to compare the relatedness of species.

Multiregional hypothesis

A dispersal hypothesis which considers that small groups of H. erectus migrated out of Africa around one million years ago, settled, remained isolated and evolved in parallel with each other. The groups periodically interbred to become the different tribes of H. sapiens we have today.

Out of Africa hypothesis

Suggests there were waves of migration out of Africa starting at one million years ago with H. erectus. These groups of H. erectus evolved into different Homo species. H. sapiens evolved in Africa about 250,000 years ago from H. erectus and migrated out of Africa around 60-90,000 years ago, replacing all other hominins as they went.

Wernicke area

Area of the brain associated with recognising and decoding speech.

Allele frequency

The proportion of an allele for a specific gene in a gene pool.

Allopatric speciation

A type of speciation where geographic isolation disrupts gene flow between two populations of a species resulting in evolution into different species.

Allopolyploid

An organism that contains two or more sets of chromosomes from two or more different species.

Amphiploid (sterile hybrid)

An amphiploid is formed by crossing two different species and is sterile. It undergoes nondisjunction in meiosis to become fertile, having two sets of homologous chromosomes, becoming an allopolyploid.

Autopolyploid

Having more than two sets of chromosomes from a single species.

Bottleneck effect

The phenomenon in which a population is dramatically reduced in size, but then rebounds again. A consequence of the bottleneck effect is the loss of alleles in a population, reducing genetic diversity.

Deme

A sub-population within a larger one that is partly isolated from interbreeding with other sub-populations present.

Evolution

Gradual change in the genetic code of populations over a long period. May result in the formation of new species.

Founder effect

A new colony is started by a few members of an original population in a new location. Allele frequencies of the new population are not representative of the allele frequencies of the original population and rare alleles may become fixed or lost.

Gause’s Competitive Exclusion Principle

No two species can occupy the same ecological niche. One will either die or change niches.

Gene flow

Occurs when individuals migrate between different populations and cause changes in the genetic composition of the resulting populations. (Immigration into and emigration out of the population.)

Genetic drift

The random change in a small population’s allele frequency from one generation to the next, due to chance. Alleles may then be fixed or lost.

Geographical isolation

Where any physical feature of the Earth prevents gene flow. For example, mountains, rivers or glaciers.

Hybrid

Individual formed through crossing two different species where the offspring may be sterile or show hybrid vigour.

Hybrid breakdown

A reproductive isolating mechanism where there is a decline in the fitness or viability of hybrid offspring in later generations (F2 and beyond) compared to the first generation (F1) hybrids.

Hybrid inviability

A reproductive isolating mechanism where hybrids fail to develop into healthy, mature adults, either in utero or after birth.

Hybrid sterility

A reproductive isolating mechanism where the hybrid reaches maturity but cannot produce viable offspring. For example, mule.

Reproductive Isolating Mechanism

An evolutionary mechanism (or inherited feature) that prevents different species from interbreeding and producing viable, fertile offspring. May be temporal, behavioural, mechanical, or gametic.

Polyploidy

Where an organism has three or more sets of homologous chromosomes.

Prezygotic isolating mechanism

A reproductive isolating mechanism that keeps species separate by acting before fertilisation occurs. For example, courtship differences.

Post-zygotic mechanism

A reproductive isolating mechanism that keeps species separated by acting after fertilisation. For example, infertile hybrid.

Ring species

A series of geographically distributed populations that exhibit a gradual change in phenotypes away from the oldest population. Neighbouring populations are able to interbreed, but the extreme ends of the series, while geographically close, are unable to interbreed.

Speciation

Process by which one species gives rise to two or more new species.

Species

A group of organisms that can breed with each other and produce fertile offspring.

Morphological isolating barrier

When reproductive structures between related species are incompatible.

Temporal isolating mechanism

When groups are reproductively isolated due to being active at different times of the day or seasons.

Vestigial structure

An anatomical feature that has no apparent function but resembles a structure of a presumed ancestor. For example, kiwi wing.

Y-chromosome

A nuclear chromosome passed down through the male line. Does not undergo crossing-over. It can be used to compare the relatedness of extant species and extinct species.