natural selection

Question 1

D4.1.1—Natural selection as the mechanism driving evolutionary change

Define natural selection and fitness.
Outline the process of natural selection and the resulting evolution of the population.
Compare the reproductive success of better and less well-adapted individuals in a population.
State that natural selection has operated continuously over billions of years, resulting in the biodiversity of life.

Answer 1

• A mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce, and pass on these variations on to the next generation. (ACTS ON PHENOTYPE)
• Fitness measures an organism’s reproductive success (how well-adapted an individual is to its purpose or role)
• In order for natural selection to occur: Variation in adaptations within a species. / Overproduction of offspring. / Survival of the best adapted individuals. / Best adapted individuals reproduce more successfully.
• SO ALL OF THEIR OFFSPRING DEVELOP THESE ADAPTATIONS, AND SO THE SPECIES HAS EVOLVED.

Question 2

Explain why Darwin’s evidence of evolution via natural selection resulted in a paradigm shift in the understanding of how life evolves.​ (think: advantageous traits!)

Answer 2

• NATURAL SELECTION ACTS ON HERETABLE CHARACTERISTICS
• Because resources are limited in nature, organisms with heritable traits that favor survival and reproduction will tend to leave more offspring than their peers, causing the traits to increase in frequency over generations.
• Natural selection causes populations to become adapted, or increasingly well-suited, to their environments over time.

Question 3

D4.1.2— Roles of mutation and sexual reproduction in generating the variation on which natural selection acts.

Define biological variation.
Explain why natural selection can only function if there is variation in a species.

Answer 3

• small differences in DNA base sequences between individual organisms within a population.
• If there was no variation within a species, then all individuals would be the same and no individual would be favoured over the other and natural selection would not take place.

Question 4

Outline sources of genetic variation (mutation, meiosis and sexual reproduction).
Compare variation that results from mutation to those that is generated from sexual reproduction.

Answer 4

• Mutations: Random errors in DNA, Errors in mitosis & meiosis, Environmental damage.
  Sexual reproduction: Mixing of alleles - Genetic recombination: new arrangements of alleles in every offspring, New combinations = new phenotypes.
• However, some mutations can influence the fitness of an organism, and these are known as beneficial or deleterious mutations.

Question 5

D4.1.3– Overproduction of offspring and competition for resources as factors that promote natural selection.

State that species have the ability to produce more offspring than the environment can support.

Use an example to illustrate the potential for overproduction of offspring in a population.

Describe competition for resources as a consequence of overproduction of offspring.

Answer 5

• Many species create many more offspring than there are resources like food, water, and living space to support them.
• Darwin studied the reproduction of elephants, one of the slowest breeding land mammals, and found that if a single female survived and reproduced at the same rate, after 750 years there could be 19,000,000 descendants of this single mother.
• This creates a struggle to survive for the offspring. Those who are better able to survive then pass on their genes to their offspring. The competition that exists among offspring to limit survival of all offspring.
• Competition for food, living space, and mates leads to adaptations of individuals.

Question 6

D4.1.4– Abiotic factors as selection pressures.

Define selective pressure.

Compare density-independent and density-dependent selective pressures.

State example abiotic selective pressures.

Outline how a selective pressure acts on the variation in a population.​

Answer 6

• external agents which affect an organism’s ability to survive in a given environment.
• density-dependent s.p. occur in biotic enviro./density-independent s.p. occur in abiotic enviro.
• ex: change in prey/predators/competitors vs. temperature/resource availability/precipitation
• both s.p.
• density-dependent - increases competition/density-independent - everyone has the same chance of being affected
• Selection pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait)

Question 7

D4.1.5— Differences between individuals in adaptation, survival and reproduction as the basis for natural selection.

Define adaptation and fitness.

Explain the effect of the selective pressure on the more and less adapted individuals in a population.

Explain adaptation as a consequence of intraspecific competition. ​

Answer 7

• inherited characteristics of organisms that enhance their survival and reproduction in a specific environment
• some individuals are better adapted and able to survive and reproduce in the presence of the selective pressure while the less adapted do not survive and reproduce as successfully.
• Competition for food, living space, and mates leads to adaptations of individuals in order to survive - to become stronger.

Question 8

D4.1.6—Requirement that traits are heritable for evolutionary change to occur

Explain why only heritable characteristics can be acted upon by natural selection.

Answer 8

• • natural selection is reliant on heritable traits because only they can be passed to offspring

Question 9

D4.1.7- Sexual selection as a selection pressure in animal species.

Outline the mechanism of sexual selection in evolution of courtship behavior and anatomical features.

Answer 9

• Sexual Selection: individuals with certain inherited characteristics are more likely to obtain mates than other individuals
  Results in sexual dimorphism (differences between sexes in secondary sex characteristics)
  Size, color, ornamentation, behavior, etc.

Intrasexual Selection: individuals of one sex (usually males) compete directly for mates
Intersexual Selection: individuals of one sex (usually females) choose a mate

• Sexual Selection Occurs When Certain Traits Increase Mating Success; attractiveness to potential male, fertility of gametes, and successful rearing of offspring

Question 10

Describe examples of sexual selection, including for color, size, and courtship behaviors.

Answer 10

• Some examples include the plumage (longer tails and deeper colour) in a peacock, which attracts mates, and the horns on a ram, which help it compete for a mate.
• birds of paradise; males exhibiting vast differences in behavior and an array of exotic feathers compared to females in order to attract them