Natural Selection, Fitness, & Adaptation Flashcards
Natural selection
Process by which adaptive structures are evolved and maintained
What is regarded as the main cause of change in organisms in relation to their environment?
Natural selection
Natural selection depends on ______
genetic variations, which originate idiosyncratically by mutation and recombination
The biased reproduction of certain genetic alternatives based on an organism’s characteristics and interactions
Natural selection
Conditions for natural selection to operate
1.) The individuals or units of selection must vary
2.) Some individuals must be more fit than others (differential fitness)
3.) There must be a correlation between the fitness of parents and offspring (heritability)
5 Observations in Origin
1.) Populations have the potential to increase exponentially
2.) But they generally maintain a stable size
3.) Resources are limited
[Struggle for existence]
4.) Variation in all species
5) Variation is heritable
[Variation makes some individuals more successful than others in the struggle; those that survive and reproduce will leave offspring that have those same variants]
*Evolution by natural selection
Darwin and Wallace’s mechanism for evolution
Natural selection
The phenomenon of ________ variation leading to a better chance of survival and reproduction
favorable
Fitness
A measure of how good an organism is at survival and reproduction (“reproductive success”)
- a number
An example of natural selection in finches
Variation in beak size and shape in a single species of ground finch
Factors: annual rainfall and number of cactus flowers by year
Variation in beak shape
- long and thin to short and thick
Beak shape affected food resource possibilities
- nectar of flowers
- bugs inside cactus paddles
El Niño event in 1983
- most cactuses fell over and rotted, causing beak size to evolve from long and thin to SHORT and THICK
Favorable
= higher relative fitness
Variation is not inherently “good” or “bad”
A variant that has high fitness in one environment might not have high fitness in another different environment
- the fitness value associated with a phenotype/genotype is ENVIRONMENTALLY DEPENDENT!
Selected for
Higher relative fitness
Selected against
Lower relative fitness
How is fitness a weighting factor?
Determines how quickly evolution will happen
Adaptation
The phenomenon of an organism being a good “fit” to its environment
Natural selection produces…
adaptation
Key points about adaptation
1.) Trait that increases the reproductive success of an organism
2.) The process of genetic change of a population, owing to natural selection, whereby the average state of a character becomes improved with reference to a specific function, or whereby a population is thought to have become better suited to some feature of its environment
3.) Improvement in function
4.) The process of successful interaction between a population and an environment
5.) An anatomical physiological or behavioral response of organisms or populations to the environment
The 3 different patterns of selection
1.) Directional selection
2.) Stabilizing selection
3.) Disruptive selection
Directional selection
Relative fitness increases toward one extreme
Stabilizing selection
Fitness is low at both extremes
Disruptive selection
Relative fitness low at intermediate phenotype/genotype; high at both extremes
- relative fitness is high at both extremes but low at the initial average
Cavet of selection
Sickle Cell Disease
Why doesn’t natural selection eliminate the HbS allele if it causes Sickle Cell?
Heterozygote advantage
