Evolution Flashcards
A4.1.1; A4.1.2; A4.1.3; A4.1.4; A4.1.5; A4.1.6; A4.1.7 (24 cards)
What is evolution?
Evolution is the cumulative change in the heritable characteristics of a population over time.
1. Heritable characteristics are traits passed from parents to offspring through genetic material (DNA).
2. Evolution operates at the population level, not on individuals, as changes accumulate across generations.
What is natural selection?
Natural selection is the process where individuals with traits better suited to their environment have higher reproductive success, passing these traits to the next generation.
What is selective breeding/artificial selection?
A form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring.
What are the evidence for evolution?
- Fossil records provide a historical record of life on Earth, showing how species have changed over time.
- Homologous structures: conserved characteristics found in different species as a consequence of common ancestry (eg. the penadactyl limb).
- Molecular evidence: comparing DNA and protein sequences across species reveals genetic similarities that align with evolutionary relationships (eg. the universal genetic code).
Evidence for evolution from genetic sequences.
1. Sequence simmilarity: When comparing DNA or protein sequences between different organisms, the more similar the sequences are, the more closely related the organisms are considered to be.
2. Divergence: Over time, mutations accumulate in DNA sequences, leading to changes in the amino acid sequence of proteins. These changes can be used to trace evolutionary relationships.
3. Cladistics analysis: By aligning and comparing DNA or protein sequences across multiple species, scientists can construct cladograms, which visually represent evolutionary relationships between organisms.
Give an example of selective breeding in a crop plant.
Corn is the result of selective breading of wild grass “teosinte”.
Humans selectively bred teosinte to soften and enlarge the kernels. Teosinte kernels are covered by a hard casing, whereas corn kernels are fleshy and easy to eat.
Give an example of selective breeding in domesticated animals.
Variations in domestic dogs. Dogs were domesticated from a grey wolf ancestor, many breeds have been bred from this single ancestoral species as a result of selective breeding by humans.
Define homologus structures and give an example.
Homologus structures are structures inherited from a common ancestor, they share common structures but may have evolved in diverse ways to become adapted for different functions, eg. the penadactyl limb.
Define the pentadactyl limb.
Limb found in tetrapods with the same general bone structure.
While there are differences in relative lengths and thickness of bones (with some cases of digit bones being lost or fused), the pentadactyl limb includes:
🟡One bone proximal to the body
🟢Two bones distal to the body
🔴Group of little bones
🟣Digit bones at the tips of the limb
Define analogous structures.
Structures or behaviors of different species that may look similar or have the same function but are not the result of shared common ancestry of the two species.
When does convergent evolution occur?
Occurs when different species independently evolve similar traits or behaviors in response to similar environmental selection pressures.
Whether the trait is homologous or analogous is typically determined by analysis of the traits of the common ancestor of two species. How?
If the common ancestor of two species had the trait and passed it along to all its descendants, then the trait is homologous within the descendant species.
If the common ancestor of two species did not have the trait, then the trait is likely analogous and independently evolved in the descendant species.
Give an example of an analogous structure.
The streamlined body shape sharks, dolphins and penguins are analogous. The similarity in structure is because the same selection pressures of the swimming carnivore niche favor a streamlined shape, not because it was inherited from a common ancestor between the species.
Define speciation.
Speciation is the process by which a population of one species diverges to become two distinct species.
Explain how speciation occurs.
As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases.
Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment.
When two populations can no longer interbreed and produce fertile, viable offspring they are considered to be separate species.
Gradual evolutionary change in a species.
The alterations of a single species over time eventually produces a population that is physically and/or genetically distinct from the original ancestor, this however is NOT speciation as there is only a single evolutionary species.
State the impact of speciation and extinction on the total number of species on Earth.
Speciation increases the number of species on Earth while extinction reduces the number of species.
List two processes required for speciation to occur.
- Reproductive isolation
- Differential selection
Define reproductive isolation.
Reproductive isolation is the first step of speciation. Populations stop inbreeding with each other. Inbreeding causes mixing of genes, whereas speciation depends on separation of gene pools.
How differential selection works?
1. Different Selection Pressures: Isolated populations experience unique environments (e.g., climate, predators, food availability).
2. Natural Selection: Traits that enhance survival and reproduction in each environment are favored.
3. Accumulation of Differences: Over time, these traits become more pronounced, leading to genetic, behavioral, and morphological divergence.
Give an example of speciation.
Bonobos and Chimpanzees are closely related species of primate who became reproductively isolated by a geographical barrier.
The two populations became exposed to different selection pressures and over many generations evolved different physical and behaviour traits:
* The chimpanzees had to compete with gorillas for food and territory – they exhibit higher aggression and form patriarchal (male-led) social hierarchies
* Bonobos did not share territory with gorillas and have consequently developed less aggressive tendencies – forming female-dominant social clusters
Types of selection pressures.
Resource availability – Presence of sufficient food, habitat (shelter / territory) and mates
Environmental conditions – Temperature, pH levels, weather and climate changes
Biological factors – Exposure to predators and pathogens (diseases)
Explain selection pressures.
Selection pressures are external agents which affect an organism’s ability to survive in a given environment
Selection pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait)
Selection pressures may not remain constant, leading to changes in what constitutes a beneficial adaptation for survival
Define adaptation in natural selection.
An adaptation is any feature that aids in the survival of an organism by allowing them to be better suited to their environment
Structural adaptations describe any physical differences in biological structure (e.g. neck length of a giraffe)
Behavioural adaptations refer to differences in patterns of activity (e.g. possums feigning death when threatened)
Physiological adaptations relate to variations in the activity of internal organs (e.g. homeothermy, colour perception)
