Evolutionary Theory and Mechanisms of Change

LUCA

Not the first lifeform, but is foundation of all life

All life shares certain molecular features (like the genetic code, ATP for energy, and certain enzymes)

Evolution

The process of genetic change in a population over many generations due to interactions with biotic and abiotic factors

Heritable Traits

Traits that are present at birth and transmitted through DNA and genes

Ex. eye colour, height

Acquired Traits

Traits that develop during an individual's lifetime (through experience) and are not inherited

Ex. scars, tattoos, learned skills

Fossil Record

Sedimentary Rock Layers contain many fossils of life forms that are extinct and are new, showing the sequence in which they evolve (ex. plants before animals)

Transitional Fossils

Fossils that show the progression of species, such as Hyracotherium and Archaeopteryx

Vestigial Structures

Structures that have no known function

Ex. small leg bones in snakes and the appendix in humans

Natural Selection

Driving force of Evolution

Homologous Structures

Structures with a shared evolutionary origin and similar developmental pathways, though they may have different functions

(Divergent Evolution)

Analogous Structures

Structures with independent evolutionary origins that have similar functions

(Convergent Evolution)

Selective Breeding (Artificial Selection)

The deliberate genetic change controlled by humans, demonstrated through domesticated animals

Ex. dogs

DNA Sequencing

A test of the differences in DNA that indicates how closely or distantly species are related

Variation

Differences in traits among organisms within a species

Adaptation

Characteristics that make an organism suited to its environment and way of life

Ex. structure (beaks)

Ex. camouflage (zebras, walking sticks)

Ex. water storage (cacti)

Mimicry

Viceroy Butterfly (harmless) and Monarch Butterfly (harmful)

Microevolution (5)

Changes in gene frequencies and phenotypic traits within a population and species

Small Population Size (2)

Founders Effect: a change in a gene pool that occurs when a few individuals start a new isolated population

Ex. Amish - polydactyly and little people

Bottleneck Effect: a population is affected by a rapid decrease or a natural disaster

Ex. cheetah population was once down to 7 cheetahs. Today, cheetahs share about 80% of their genes.

Non-random Mating (2)

Some organisms are more likely to mate than others

Plant Self Pollination: Can occur in plants where the stamen and the carpel mature at the same time.

Sexual Selection: Different levels of reproductive success, caused by variation in the ability to obtain mates.

- Often results in sexual dimorphism _Males and females of the same species that are very different in appearance.

- Mating and courtship behaviours.

Ex. Bighorn Sheep

Ex. Cardinal Colours

Mutations (1)

Changes in the DNA sequence that can lead to new traits

Ex. Mosquito resistance to DDT

Ex. Bacterial STD resistance to antibiotics

Gene Flow Migration (1)

Movement of an organism from one population to another, affecting genetic diversity

Natural Selection (process explained)

Natural selection = organisms with advantageous traits survive/reproduce more

1. Variation exists in populations (genetic differences)

2. Overproduction of offspring → competition

3. Some traits give a survival advantage (adaptations)

4. Fittest individuals pass on their traits

5. Over generations, populations change = evolution

6. Leads to better adapted species

Directional Selection (Peppered Moths England)

Natural selection that favours the phenotype at one end of the range. results in observable change in population

Ex. giraffe neck length, moth wing colour, horse size

Disruptive Selection

Favours both extremes of the range and tends to eliminate the intermediate phenotypes. results in split gene pool, potentially formation of a new species

Ex. fur colour of mice (white areas and black areas)

Stabilizing Selection

Favours individuals near the middle of a range of characteristics, resulting in a narrower phenotype range. Results in a narrower phenotype range (Genetic variation is reduced). Improves adaptation to environmental factors

Ex. 1 pup per bat

Ex. ~7 lbs per human baby

Speciation (Darwin's Finches) (2)

Formation of new species from existing species.

Sympatric Speciation

Evolution of populations within the same geographic area into separate species.

Ex. Cichlid fish in East Africa

Allopatric Speciation (2)

Population that is split into two or more isolated groups by a geological barrier.

Ex. Kaibab squirrels (north and south Grand Canyon)

Prezygotic Mechanisms (3)

Impede mating or prevent fertilization, thus no zygote is formed.

Behavioral Isolating Mechanisms: Actions are different thus there is an inability to attract a mate. Ex. Bird songs.

Temporal Isolating Mechanisms: Different breeding times. Ex. Similar plants that flower at different times.

Geographic Isolating Mechanisms: living in different habitats. Ex. Garter Snakes that live in a field vs. near water.

Postzygotic Mechanisms (3)

Prevent a fertilized egg from growing into a viable adult.

Zygotic Mortality: an embryo forms but does not survive. (Most often aborted) ex. Frog species

Hybrid Inviability: the offspring do not live long. Ex. Sheep and goats mating to produce offspring.

Hybrid Sterility: offspring of two genetically similar parents survive, but they are sterile.

Ex. Female horse and a male donkey create a mule, Male horse and a female donkey create a hinny

Polyploidy

More than two full sets of chromosomes. Ex. strawberries

Adaptive Radiation

Single ancestral species diversifies into multiple new species, each adapted to different ecological niches. (quicker form of divergent evolution)

Convergent Evolution

Unrelated species independently evolve similar traits due to similar environmental pressures

Divergent Evolution

Common ancestor evolves into different species with distinct traits