Biological fitness/ natural selection

What is evolution

Development of species over the years

Ways to prove evolution is real

1. Comparative anatomy

2. Fossil records

3. Embryology

4. DNA analysis

Pentadactyl limb

similar bone structure, thats shared, different functions.

Structures are called homologous, since they are evidence at one point that species has a common ancesteror but the species have diverged.

What are homologous structures?

Structures with a similar underlying structure inherited from a common ancestor, showing that species have diverged.

What are analogous structures?

Structures with the same or similar function but different structures and evolutionary origins.

What is convergent evolution?

When unrelated species independently develop similar adaptations because they live in similar environmental conditions. Example: shark fins and dolphin flippers.

Homologous vs analogous structures?

Homologous: similar structure, common ancestor, different functions possible.

Analogous: different structure/origin, similar function, caused by convergent evolution.

Lamarckian evolution

1. Change in environment = led to use of some certain organes and disuse of other among organisms

2. Organs that were used more increase in size over the lifetime of the organisms. Organs that are not being used over lifetime would shrink.

3. Change over lifetime of an individual would be passed on to the offspring. 

Darwinian evolution

 - more offspring produced can be supported by the environment. The “overproduction” leads to competition for natural resources. Leads to stable levels of deaths and births. 

- individuas in a population arent identical but show variations in their characteristics. 

- variation genergated through random mutation in germline cells. FUrther variation,    w            is by randomness of mating, crossing over, independent assortment.

- Individuals with variation help them adapt better to the environemnte, so they are more likely to survive, reproduce and pass the positive variation to the offspring. Also individuals with less favourable variations are less likely to survive. Called natural selection.

- Eventually, in a particular environemnt, individuals with more favourable variations will form a larger proportion of the population.

- Over many generations, natural selection leads to populaytops adapted to specific environments

Selection pressures

Environmental factors (can be abiotic or biotic) that affect an individual’s chance of surviving and thus reproducing. They basically “select” which traits are more advantageous for that environment.

5 Density dependent factors.

1. Availability of food

2. Availability of water, shelter, and other resources,

3. Presence of predators

4. Spread of pathogens???

5. Finding of mates

Density-dependent factors are factors whose effect gets stronger as population density increases.

For example, if food becomes scarce, individuals that are better at competing for food may survive and reproduce more. Over time, traits that improve competition, disease resistance, or avoiding predators can become more common.

4 Density independent factors

1. Natural disasters like wildfire or volcanic eruptions

2. Temperature

3. Carbon dioxide and oxygen levels

4. Pollution

Density-independent factors affect a population regardless of how dense or crowded it is.

With density-independent factors, the pressure comes from the environment rather than crowding. For example, if a sudden cold period occurs, individuals with traits that help them tolerate low temperatures may survive better and pass those alleles on.

^^ Abiotic factors

Carrying capacity

Maximum size of population that an environment can hold/support over time due to its available land/resources and environmental conditions.

Overproduction of offspring

More offspring are produced than the carrying capacity can hold, so some die off. This creates competition for resources, and individuals with more advantageous traits will survive to reproduce, allowing for natural selection. Without competition, there is no drive for evolution.

Intraspecific competition

Competition between individuals of the same species for limited resources, usually because of overreproduction.

What is a gene pool

A combination of all alleles present in a reproducing population of a species.

what is the frequency of an allele

The frequency of an allele is how common that variation of the gene is in a given population. 

Hardy Weinberg calculation of frequency of allele X

Number of copies of allele x in population/total number of copies of the gene in the population

Can use this to determine how alleles have changed over generations (evolution)

Why do allele frequencies change

Natural selection or random events

Stabilizing selection

Stabilizing selection favors the intermediate/average phenotype and selects against both extremes.

Example: human birth weight: very low and very high birth weights have lower survival than intermediate weights.

Directional selection

Directional selection favors one extreme phenotype.

Example: darker moths survive better in the industrial revolution due to the soot, so the population gradually becomes darker through natural selection

Disruptive/ diverging selection

Diverging selection favors both extremes and selects against the intermediate phenotype.

Example: birds with either very small or very large beaks do well, while medium beaks are less useful.

What is adaptive radiation

 Adaptive radiation is an evolutionary process where a single ancestral species rapidly diversifies into a multitude of new forms as they adapt to different ecological niches and exploit new resources

Conditions affecting equilibrium

Allele frequencies will remain the same if:

• No mutations bringing in new alleles

• There is random mating.Non random mating is the norm in most populations (sexual selection)

• Natural selection cannot occur

• No genes should enter or leave the population

• The population must be large as in small populations genetic drift or chance events can change allele frequencies

What is a genetic drift

Random changes in allele frequency caused by some random event. Not natural selection because it doesn’t rely on a more advantageous phenotype

Bottleneck effect

the gene pool represents the survivors of a random event EX: northern elephant seals

Founder effect

a small subset of a population breaks away from the larger population and colonizes a new area, passing on their genes at a higher frequency. Ex: Dutch immagrants in South Africa

Speciation

Speciation is the process where one species splits into two or more different species that cannot reproduce together if they meet again, reproductive isolation. There are two different types that decide how that reproductive isolation begins.

Allopatric speciation

Allopatric speciation occurs when a population of a species is split by a geographical barrier (geographical isolation), preventing the exchange of genetic material

Sympatric speciation

Sympatric speciation is when a new species is formed within the same location due to isolating mechanisms (behavioral isolation and temporal isolation)

• Behavioral isolation: mating rituals not recognized by individuals so they do not interbreed.

• Temporal isolation: differences in timing of reproductive cycle, like mating seasons or gamete production

Factors that determine biological fitness

1. The environment in which the individual (genotype) lives

2. The survival value of an individual

3. Reproductive potential of an individual