7. Evolution Flashcards
Evolution
Changes in the heritable characteristics of an organism over generations
Speciation
Theory of evolution states species do not remain the same
Can occur due to reproduction isolation
When gene flow stops, genetic differences can accumulate between 2 populations
Natural Selection
Process through which populations of living organisms adapt and change
—> Heritable characteristics are passed through generations
Reproduction Isolation
When exchange of genes or gene flow between populations of species is prevented
Gene flow
Movement of genes from one population to another
Selection Pressure
Thing in organism’s environment that may affect it’s ability to survive
Ex. Predator
When has speciation said to have occurred?
When 2 organisms of 2 different populations cannot successfully interbreed
Extinction
Reduces diversity and reduces number of species on Earth
Reproductive isolation
Occurs due to change in an organism’s alleles or phenotype which prevents it from successfully breeding with individuals that don’t have these changes
—> Can occur due to geographical isolation of population
Example of speciation event
Bonobos and Chimpanzees
Chimpanzees are found to the North of Congo river and Bonobos to the South
Chimpanzees are more aggressive. This could have been a reason due to more competition for resources
Chimps have male dominated social structures while Bonobos have dominant females
Geographical isolation
A physical barrier separates populations of a species, which can lead to the evolution of new species. This process is called allopatric speciation
Ex.
Natural: Body of water (river), Mountains
Manmade: Motorways
2 populations may be affected by different selection pressures
Types of Speciation
Divergent –> Single ancestor splits to different lineages Ex. Darwin Finches
Convergent –> Unrelated species have similar traits due to similar selection pressures Ex. Streamlined body of sharks and dolphins
Parallel –> Closely related species developing same traits due to similar selection pressures
Coevolution –> Two species evolve in response to each other becomes a reciprocal relationship Ex. Predator Prey (Predator evolves to better capture prey and prey evolves for defence to evade predator)
Theories of evolution
1) Darwinian Evolution
2) Lamarckian Evolution
Darwinian Evolution (4)
-Individuals in a species show a wide range of variation due to random mutations in their DNA
-Individuals within a population must compete for survival due to selection pressures
-Individuals with characteristics most suited to the environment have a higher chance of survival and are more likely to reproduce
-Over many generations, the advantageous alleles become more frequent in a population
Lamarckian Evolution (4 & example)
-Idea that changes that occur in a organism during its lifetime can be inherited.
-Acquired characteristics
-Characteristics used frequently by an organism, becomes stronger and better while a characteristic not being used gradually disappears
-Beneficial characteristics are passed
Ex. Giraffe had short neck, it started reaching for higher leaves and slowly neck got elongated and passed to the next generations
Why was Lamarckian’s ideas wrong?
Since they lack concept of heritability. Acquired characteristics are not passed to offspring
2 Evidences of Evolution
Comparing DNA
Homologous Structures
Comparing DNA: Evidence (3)
- Similarities in sequence data across different species indicate all living species have common ancestor
-Species that share more similarity in their DNA sequences are likely to have diverged from a common ancestor
-Conserved sequences are found in a majority of organisms from Bacteria to Humans- reinforcing idea of a shared evolutionary history
Homologous Structures: Evidence
May look and function very differently but share a common ancestor: Pentadactyl limbs
Human Impact on Evolutionary Process
Climate Change
Artificial Selection
Climate Change
-Altering ecosystems and habitats
Warmer temperature forcing artic species like polar bear to adapt quickly
Ex. Polar Bear
Facing evolutionary pressure due to melting sea ice
They adapting by having smaller body size (due to food availability)
Artificial Selection
Humans deliberately choose specific plants and animals to breed for desirable traits. Selective breeding animals with more milk, more wool, etc.
In plants it is for more crop yield and disease resistance
Impacts of artificial selection
-Smaller gene pool: Leads to less genetic diversity and can make populations vulnerable to disease and environment changes
-Can boost economic value due to more and better product in a short time frame
- In the long term it can affect a lot of people due to decreased resilience to disease.
Ex. Irish Potato Famine in 1940 where people depended on one type of potato which was vulnerable to disease
