Lecture 2B: Evolution Flashcards
What is the exact definition of evolution (for this class)?
A change in heritable characters in a population over time
What did Darwin mean by “Descent with modification”? How is this related to his hypothesis that all living things share a common ancestor that lived in the past?
All species are descendants of ancestral species that were different from present-day species.
Darwin hypothesized the unity of life after observing that many organisms share similar characteristics. He believed that descendants of that ancestral organisms inhabited various regions and over generations, developed different modifications (adaptations) that best suited their environments and ways of life.
What are the 2 observations Darwin made from studying artificial and natural selection? Explain them.
- members of a population often vary in their inherited traits
- every individual of a population is born different than any other from that population, even if they share the same parents, the genetic information and inherited traits will differ, even if slightly. Natural selection will favour the heritable traits that can improve survival and reproduction. If there were no variation between individuals in a population, the population would not evolve. - all species can produce more offspring than the environment can support and many of these offspring fail to survive and reproduce
- if an offspring does not inherit the traits to survive and reproduce, it will die off so the individuals that have the traits can survive and reproduce.
What are the 2 inferences Darwin made based off his observations of natural selection?
- Individuals whose inherited traits give them better chances at survival and reproduction have more offspring than those who did not inherit those traits
- the unequal ability of individuals to survive and reproduce will lead to an accumulation of favourable traits in the population over generations (adaptations)
What is natural selection? example
Natural selection is one mechanism by which evolution occurs.
ex. How a species of bird becomes more camouflage in its environment over time to be better protected from its predators
What is artificial selection? example
When humans select and breed individuals of a population that possess a desirable trait so as to pass on that trait to the next generation and increase it within the population overtime.
What does evolutionary fitness mean?
An organism’s ability to reproduce and survive, but mostly defined by the ability to reproduce healthy, viable offspring or many offspring
What are the 3 conditions for natural selection to cause a population to evolve?
- There must be a character variation in the population
- The character variation must be heritable
- There must be fitness differences between the individuals with character variations (different traits)
Why are the 3 conditions required for natural selection to cause evolution of a population to occur?
- If there is no character variation in the population, there is no variation amongst the population that can increase survival and reproduction so there will be no change in the population over time
- If a character variation is not heritable and was instead gained throughout the parents’ lifetime, there is no guarantee the offspring will receive that character variation and the chances of that character variation increasing in the population and changing the pop. over time, is very low.
T or F: natural selection evolves adaptations within an individual’s lifetime? Explain
FALSE.
Evolution by natural selection is a change in a POPULATION OVER TIME. An individual will not gain more fit genes throughout their lifetime.
What is another way to refer to the process of evolution by natural selection?
Adaptation…because, adaptations are an inheritable trait that increase within a population through evolution and natural selection
T or F: When a population has evolved through natural selection, it is referred to as having become ADAPTED to its environment?
TRUE
Why are the 3 conditions required for natural selection to cause evolution of a population to occur?
- If there is no character variation in the population, there is no variation amongst the population that can increase survival and reproduction so there will be no change in the population over time
- If a character variation is not heritable and was instead gained throughout the parents’ lifetime, there is no guarantee the offspring will receive that character variation and the chances of that character variation increasing in the population and changing the pop. over time, is very low.
- There must be fitness differences between the individuals with character variations so one of the character variations can increase and the other can decrease. Individuals with the beneficial character variation will be able to survive and reproduce more offspring, allowing the individuals with the less fit variation to decrease and overtime, the population with the least fit character variations will decrease.
T or F: contribution of a trait to an INDIVIDUAL’S fitness is dependent on their environment. Explain
TRUE, if the environment changes, what is considered adaptive changes too…
ex. the blue birds were safer from predators in the blue bushes, so the blue bird population increased over time (due to natural selection by evolution), but if the environment changes to red bushes, the blue birds are at a serious disadvantage and the adaptive benefits change.
Heritable traits are passed down from ____ to ___. These traits are determined ____, rather than being acquired during an individual’s life.
Passed down from PARENT to OFFSPRING
Determined GENETICALLY
