Natural Selection (meg)

Question 1

What is natural selection?

Answer 1

Natural selection is the process where individuals with traits that provide an advantage in survival and reproduction are more likely to pass those traits to the next generation. This leads to the evolution of advantageous traits over time.

Question 2

What was Darwin’s definition of natural selection?

Answer 2

Darwin described natural selection as:
- Variations that are beneficial to an individual in its ecological context increase its chances of survival.
- These traits are often inherited by offspring, leading to a greater survival advantage in future generations.
- Only a small proportion of individuals survive and reproduce due to competition

Question 3

What role did Malthus’ ideas play in Darwin’s concept of natural selection?

Answer 3

Malthus proposed that populations grow faster than resources, creating a struggle for survival. Darwin applied this idea to all organisms, observing that only those with advantageous traits survive and reproduce.

Question 4

What is fitness in the context of natural selection?

Answer 4

Fitness refers to an individual’s ability to survive and reproduce. Differences in fitness arise when traits influence survival and reproductive success.

Question 5

How is natural selection measured?

Answer 5

By observing a correlation between a trait (e.g., beak size, fledging mass) and fitness (e.g., survival or reproductive success).

Question 6

What is the relationship between natural selection and evolution?

Answer 6

Natural selection acts on existing variation, favoring advantageous traits. Over generations, this leads to the transmission of these traits and results in evolution.

Question 7

Define: teleology

Answer 7

an explanation of things based on their end goal rather than by their causes or processes- assumes things happen for a predetermined reason

Question 8

Why is teleology (final causation) not part of natural selection?

Answer 8

Natural selection is not goal-directed. Traits become more or less common due to changes in the environment and differential survival, not because of a predetermined purpose.

Question 9

What are the three conditions for natural selection to occur according to Endler (1986)?

Answer 9

1. Variation: Individuals in a population must vary in some trait (e.g., morphological, behavioral, physiological, life history).
2. Fitness differences: The trait must be consistently associated with differences in reproductive success, survivorship, or fitness.
3. Inheritance: There must be a consistent relationship between the trait in parents and offspring, independent of shared environmental effects.

Question 10

What is a trait in the context of natural selection?

Answer 10

A trait is any identifiable aspect of an individual’s phenotype, including morphological, behavioral, physiological, life history, or immunological features. Traits can vary genetically or environmentally.

Question 11

What are fitness differences in the context of natural selection?

Answer 11

Fitness differences refer to the relationship between a trait and the organism’s ability to survive, reproduce, or succeed in mating.
For example:
- Fledging mass correlates with survival.
- Larger testicle size in Soay sheep correlates with higher reproductive success.

Question 12

What does inheritance mean in natural selection?

Answer 12

the degree to which traits are passed from parents to offspring due to genetic coding, independent of environmental effects. It reflects the genetic contribution to the phenotype.

Question 13

What is heritability, and how is it measured?

Answer 13

Heritability is the proportion of phenotypic variation in a population that is due to genetic differences.
Heritability (h²) = Genetic variance / Total phenotypic variance.

Question 14

What did Galton’s study on heritability demonstrate, and why was he confused?

Answer 14

• Galton attempted to quantify heritability using regression analysis by studying the relationship between parents’ and offspring’s traits, such as height- slope of regression line = degree of heritability
• He expected a perfect 1:1 inheritance (offspring being exactly as tall as their parents) but found that offspring regressed toward the mean (population average)
  Confusion = He did not fully understand that inheritance is influenced by both genetic recombination and environmental effects, which create variation and prevent traits from being perfectly continuous.

Question 15

How do genes and the environment interact in shaping traits?

Answer 15

• Phenotypes result from both genetic and environmental contributions.
• Recombination and environmental variation increase diversity, preventing traits from being completely continuous across generations.

Question 16

What are the expected outcomes if the conditions for natural selection are met, based on Endler (1986)?

Answer 16

If natural selection operates on a trait:
1. The trait frequency will vary across different age classes or life stages, more than expected from just development.
2. If the population isn’t at equilibrium, offspring traits will differ from those of their parents in predictable ways, considering variation and inheritance.

Question 17

How does Haldane (1954) define natural selection?

Answer 17

Natural selection is the differential survival or reproductive success of phenotypes. It acts on phenotypes, favoring one genotype over another, but can also occur without favoring specific genotypes.

Question 18

What is the difference between natural selection and evolution?

Answer 18

Natural selection is the mechanism through which evolution happens, but natural selection itself is not evolution. Evolution refers to changes in populations over time, which may be driven by natural selection.

Question 19

What are the empirical methods to detect natural selection?

Answer 19

1.Direct measurement through observations of population changes.
2.Patterns and inferences: Observing population size, survival rates, and environmental factors to infer natural selection in action.

Question 20

How was natural selection observed in the medium ground finch?

Answer 20

The population on Daphne Major island experienced a drought:
- Pattern: The population declined due to food scarcity (seed abundance).
- Inference: The decline was a result of food (seeds) running out, and finches with different beak sizes were better or worse at accessing the available food.

Question 21

How did seed abundance affect finch survival during the drought?

Answer 21

As seed abundance decreased over time, finches were forced to adapt. The change in seed types (harder or larger) favored finches with appropriate beak traits, demonstrating natural selection based on food availability.

Question 22

How can rapid morphological evolution be seen in response to environmental changes?

Answer 22

Over time, traits such as body size in finches evolved in response to changing conditions, like food availability. This is seen through patterns in seed hardness and depth, which influenced the survival of individuals with larger or stronger beaks.

Question 23

What is the use of Principle Component Analysis (PCA) in studying evolutionary traits?

Answer 23

PCA combines multiple body measurements (like leg length, weight, head size) into a single measurement (e.g., body size). It’s used to track morphological changes over time in response to selection pressures.

Question 24

How did body size change in the medium ground finch population?

Answer 24

Over time, average body size increased due to natural selection favoring larger individuals, likely because smaller finches were less able to survive the harsh conditions.

Question 25

What does the decrease in population size indicate about sample size and statistical error?

Answer 25

As the population decreases, the sample size also decreases, which increases statistical error (wider error bars) and makes it harder to get precise measurements of population traits.

Question 26

Why is there a skewed sex ratio in the medium ground finch population?

Answer 26

Males are generally larger than females. As more females die due to environmental pressures, the population becomes skewed towards more males, which is a result of natural selection acting on size.