Mechanisms of Evolution: Genetic Drift vs. Natural Selection

Flashcards covering key concepts from the lecture on microevolution, natural selection, genetic drift, and different types of selection including sexual selection.

Microevolution

Any change in allele frequencies over time in a population, representing the lowest scale at which evolution can operate.

Allele Frequencies

The relative proportion of different alleles (gene variations) within a population.

Natural Selection

A highly non-random process where individuals with advantageous genotypes in a specific environment have better reproductive success, leading to changes in allele frequencies over time.

Genetic Drift

A random process of evolution characterized by random fluctuations in allele frequencies due to chance events in survival and reproduction, especially significant in small populations.

Darwin's First Observation (Natural Selection)

Organisms produce more offspring than the environment can possibly sustain, leading to a struggle for survival and reproduction.

Darwin's Second Observation (Natural Selection)

Individuals within populations vary in their heritable characteristics, meaning there is genetic variation in every population.

Darwin's First Inference (Natural Selection)

Individuals with advantageous combinations of alleles (traits) for a particular environment will have greater reproductive success, producing more offspring.

Darwin's Second Inference (Natural Selection)

Over time, advantageous alleles that lead to greater reproductive success will increase in frequency in the population as long as those environmental conditions persist.

Genetic Variation

The inherent differences in heritable traits among individuals within a population, which preexists any environmental change and is the raw material for selection.

Pesticide Resistance

A classic example of rapid evolution where, over time, the proportion of individuals genetically resistant to pesticides (like DDT) in a mosquito population increases due to natural selection.

Directional Selection

A type of natural selection where the environment favors one extreme expression of a trait, causing the mean expression of that trait in the population to shift over time towards that extreme.

Disruptive Selection

A type of natural selection where intermediate expressions of a trait are selected against, while extreme expressions (both low and high) are favored, leading to a bimodal distribution of the trait.

Stabilizing Selection

A type of natural selection where extreme expressions of a trait (both too low and too high) are selected against, and intermediate or average expressions are strongly favored, resulting in a narrow range of trait expression within the population.

Sexual Selection

A subset of natural selection where certain traits increase an individual's success in obtaining mates, often leading to pronounced differences between sexes (sexual dimorphism).

Intrasexual Selection

Selection occurring within the same sex, typically involving competition (e.g., male-to-male combat) for access to mates or resources that attract mates.

Intersexual Selection

Selection occurring between the two sexes of the same species, almost always expressed as mate choice (e.g., females choosing males based on specific traits).

Runaway Selection (Fisherian Runaway)

A hypothesis proposing that an initial genetic preference for a certain trait in one sex (e.g., long tails in males) leads to a self-reinforcing cycle, driving the exaggerated evolution of that trait over time, even if it becomes costly.

Sexy Sons Hypothesis

An idea related to runaway selection where mothers benefit by producing attractive sons, as these sons will have more mating opportunities, even if the attractiveness trait itself has little adaptive value beyond mate attraction.

Good Genes Hypothesis

A counterargument to the idea of irrational mate choice, suggesting that attractive traits in one sex (e.g., elaborate plumage) are honest signals correlated with the overall genetic quality, health, or fitness of the individual, benefiting the offspring.