*natural selection and how it works

Question 0

Define Natural selection

Answer 0

is the gradual process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution.

-those individuals with favourable variations would surive, those with unfavourable variations would not

Question 1

Why did Darwin begin to doubt his belief of fixity of species?

Answer 1

• He came across fossils of ancient giant animals that, except for size, looked very much like the species that still lived in the same vicinity
• these similarities caused him to speculate that the fossils represented ancestors of those living forms,

Question 2

Darwin’s Finches: Modification from one species to many

Answer 2

• During a stopover at the Galápagos Islands, off the coast of Ecuador Darwin noticed that the birds shared many similarities with those on the South American mainland, yet weren’t identical to them. The birds varied from island to island.
• Darwin collected 13 varieties of Galapagos finches. It was clear that they represented a closely related group; but some of their physical traits were different, particularly the shape and size of the beaks.
• It was not until after the voyage that Darwin recognized the significance of the variation in beak structure.
• Darwin realized that the variatous Galapagos finches had all descended from a common mainland ancestor and had been modified over time in response to different island habitats and dietary preferences

Question 3

Darwin’s definition of natural selection

Answer 3

“It at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formulation of a new species”

Question 4

Explain why Darwin called his theory “Natural selection”

Answer 4

• The concept of natural selection was borrowed from animal breeders, who choose, or “select”, as breeding stock those animals that possess certain traits they want to emphasize in offspring. Animals with undesirable traits are “selected against”, or prevented from breeding.
• Darwin applied his knowledge of domesticated species to naturally occurring ones, and he recognized that in undomesticated organisms, the selective agent was nature, not humans.

Question 5

Define fitness

Answer 5

Pertaining to natural selection, a measure of the relative reproductive success of individuals. Fitness can be measured by an individual’s genetic contribution to the next generation compared with that of the other individuals.

Question 6

Darwin’s Basic processes of evolution

Answer 6

1) All species are capable of producing offspring at a faster rate that food supplies increase
2) There is a biological variation within species
3) In each generation more offspring

Question 7

The medium ground finch of the Galapogos Islands - An example of natural selection

Answer 7

• In 1977, drought killed many of the plants that produced smaller seeds favoured by these birds.
• The forced the population of finches on one island to feed on larger and harder seeds.
• More smaller beaked birds died than larger birds
• Although overall population declined, average beak thickness increased in the survivors and their offspring.
• The pattern in beak sized reversed itself in 1982 during heavy rains, as smaller seeds became more plentiful.

This demonstrates how reproductive success is related to environmental conditions.

Question 8

The fundamentals of evolutionary change produced by natural selection

Answer 8

1) A trait must be inherited if natural selection is to act on it.
2) natural selection cannot occur without population variation in the inherited characteristics.
3) Fitness is a relative measure that changes as the environment changes.
4) Natural selection can act only on traits that effect reproduction.

Question 9

The Mechanism of Natural selection

Answer 9

Individuals in a population vary in most inherited characteristics (i.e., they don’t all express these traits in the same way)
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Some individuals have higher reproductive success than others because they possess advantageous expressions of certain traits
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Increase in the proportion of individuals with the advantageous expression of the trait; decrease in the proportion having a less beneficial expression