Lecture 5 - Natural Selection Flashcards
(30 cards)
What are the components of natural selection?
Heredity
variation
Competition
What does natural selection lead to?
Impact on the gene pool
Impact on phenotypes and how it leads to optimally designed individuals
What are the three modes of selection?
Purifying
Stabilising
Directional
Explain purifying selection
A form of negative selection that removes harmful mutations from a population, helping preserve essential functions.
Explain stabilising selection
A mode of selection that favors the intermediate trait values and selects against both extremes.
Explain directional selection
A type of selection that favors traits differing from the current average, causing population change.
Variation-reducing effect in all 3 types of selection:
Purifying: effect most obvious, weeds out new mutations
Directional: also decreases variation as drives towards fixation of highest fitness alleles
stabilising: eliminates genetic variation
Negative frequency-dependent selection
Rare phenotypes have higher fitness than common ones.
This balances out trait alllowing it to stay stable
How does selection produce design?
Selection produces design by acting as a non-random process that incrementally improves biological traits through repeated cycles of variation and survival-based filtering. The result is traits that look and function as if designed, even though no conscious designer is involved.
Outline the 4 examples of how evolution does not always produce optimal design?
Time lags
Inconsistent selection
Genetic correlations
Shape of the adaptive landscape
Explain time lags as an example of non-optimal design
The sperm whale with the femur and pelvis - serves no purpose
Evolution can be slow to catch up with rapid environmental changes. Even though natural selection can produce well-adapted traits, it does so gradually.
Explain the inconsistent selection example of non-optimal design
2 grasshoppers with different phenotypes, green grasshopper camouflages better than a black grasshopper
Explain the genetic correlations example of non-optimal design
Siberian farm fox experiment shows that selecting for one trait (tameness) can unintentionally cause other traits (e.g., floppy ears, curly tails, coat color changes) to appear due to genetic correlations. These traits are not necessarily adaptive, demonstrating how evolution can produce non-optimal designs as side-effects of linked genes.
How does genetic correlation affect phenotype evolution?
Phenotypes reflect trade-offs between different traits that are genetically linked.
What is the adaptationist stance?
a perspective that emphasizes the role of natural selection in shaping the characteristics of organisms, including their behaviors, traits, and physiological features.
This perspective suggests that many aspects of an organism’s biology can be understood as adaptations - traits that have evolved because they conferred some advantage to individuals in their environments, increasing their chances of survival and reproduction.
How can adaptations be studied?
Via experiments
experiments of nature
comparative evidence
As well as motivation, what other ability occurs in sign stimuli?
Learning:
Preferred foods are learnt, spatial learning, emotionally charged places
How can we test hypothesis about evolutionary function?
Using reverse engineering - you see a problem and refer all the way back to its design to find the problem
What is reverse engineering? Human melanin and skin colour example
By examining melanin’s structure (UV absorption) and distribution across human populations, reverse engineering suggests that the function of melanin is to regulate UV exposure—balancing the benefits of Vitamin D production and the costs of folate destruction. Skin colour is an adaptive trait shaped by this trade-off.
What does the comparative pattern of skin colour and UV exposure support?
It supports the adaptive hypothesis that skin colour evolved in response to UV exposure.
Why is “for the good of the species” a misconception in evolution?
Because natural selection acts on individuals, not species. Traits evolve if they benefit individual reproductive success, not because they help the group.
pleiotrophy
when one gene affects multiple traits
mutation-selection balance
interaction between mutation introducing variation and selection reducing it
comparative evidence of the adaptionist hypothesis
light skin - reflects uv light as less uv surrounded
dar skin - less reflectance of uv as uv is absorbed
