Natural Selection Flashcards
KEY POINTS
- Adaptation by natural selection
- Species can change
- Species evolve from other species through the mechanism of natural selection
DARWIN’S FOUNDAMENTAL CONTRIBUTUON TO EVOLUTION
Adaptation; provided a mechanism for organic evolution
DARWIN’S THREE POSTULATES:
1) Individuals compete because resources are finite
2) Individuals vary in ways that affect their ability to survive
3) Some of this variation is heritable
ADAPTATION
a trait that is shaped by natural selection and allows the individual to survive and reproduce more successfully
PEPPERRED MOTH
The black variant is introduced in mid-1800s, their dark forms made them less visible to predators, and allowed them to camouflage with by trees covered in soot
INDUSTRIAL MELANISM
the darkness (of skin, feathers, fur) acquired by a population of animals living in an industrial region affected and darkened by soot
PEPPERRED MOTHS: COMPETITION, VARIATION, HERITABLILITY
- COMPETITION
- Predations strong selection pressure - VARIATION
- Dark and speckled forms in original population
- In this environment, melanism gives advantage - HERITABILITY
- Melanism is inherited as a simple Mendelian dominant allele
GALAPAGOS FINCHES
These birds’ diet were cracked seeds they would consume
During drought, the only available/remaining seeds were the tougher, harder seeds. Only the birds able to crack and open the harder, tougher seeds survived
GALAPAGOS FINCHES: COMPETITION, VARIATION, HERITABLILITY
- COMPETITION
- Competition for seeds leads to “struggle” for survival - VARIATION
- Large beaks confer advantage = differential survival - Variation in beak depth is heritable
TYPES OF SELECTION
directional selection, disruptive selection, stabilizing selection
DIRECTIONAL SELECTION
favors only one extreme version of a trait
DISRUPTIVE SELECTION
favors both opposite extreme variations of a trait
STABILIZING SELECTION
favors individuals with average traits, selects against extreme traits
MISUNDERSTANDINGS: COMPLEX TRAITS
Natural selection can’t explain the evolution of complex traits
- Complex adaptation don’t evolve all at once
MISUNDERSTANDINGS: UNIT OF SELECTION
- Natural selection occurs at the level of the individual
- Individuals selected for or against
- Evolution occurs at the level of the population
- Changes in gene frequencies
- Population level changed over a period
of time
MISUNDERSTANDINGS: ALL TRAITS ≠ ADAPTIVE
- Not all traits count as adaptations
- It is only an ‘adaptation’ if it contributes to fitness
- Some traits are former adaptations
- Some traits are just simply traits
(e.g. human chin, colour of our bones/teeth)
MISUNDERSTANDINGS: EVOLUTION ≠ PROGRESS
- Evolution does not always progress in one direction
- No such thing as “better”
- Only better suited to a particular environment
- Doesn’t always change in the same direction, natural selection has no foresight
- Natural selection is directly linked to the environment, which fluctuated over time
LIMITS OF DARWIN
- Couldn’t explain mechanisms of 2/3 of the postulates
- Couldn’t explain how variation was maintained
- Could not explain how traits were passed down (mechanism of inheritance)
HOW COMPLEX TRAITS EVOLVE
- Evolved in small steps through natural selection
- Demonstrates each change, building on previous small changes, can produce complex adaptations
ARTIFICAL VS NATURAL SELECTION
- Natural selection affects the entire population of a species
- Natural selection results in a large amount of biological diversity.
- Artificial selection only affects the selected individuals
- Artificial selection only brings desirable changes and desirable traits and brings a decrease in genetic diversity
CONVERGENCE
Similar traits evolve in unrelated species due to similar selection pressures
Occurs when organisms that aren’t closely related evolve similar features/behaviors, often as solutions to the same problems.
