Natural Selection Flashcards
natural selection explains …
- every adaptation
- adaptation is step-by-step
examples of natural selection
- the human eye
- immune system
- how fish evolved limbs and whale flippers
who came up with natural selection?
Darwin, with the help of Wallace
artificial selection
an evolutionary process in which humans consciously select for or against particular features
natural selection is not a ______, its a _____________
force, multi-step process
natural selection
a difference between the survival & reproduction of individuals with certain phenotypes compared to individuals with other phenotypes
natural selection main points
- individuals vary in phenotype
- some of this phenotype variation is heritable
- the variable, heritable traits affect an individuals probability of leaving offspring
equation: individuals vary in phenotype
- coefficient of variation
CV = standard deviation / mean
example of phenotypic variation being heritable
you look like your parents, not random people
struggle for existence
- not all individuals survive to reproduce or reproduce maximally
- there is a leading struggle for existence, leading to variability in reproductive output
outcome of natural selection
genetic composition of the population changes across generations
what do traits under natural selection impact?
the probability of survival and reproduction
what does natural selection operate on?
the phenotypes of individuals within a population, while populations evolve across generations
natural selection can operate even if …
the characters under selection are not heritable
natural selection is …
a process composed of testable components
why do individuals vary in phenotype?
variation could be due to genetic factors, environmental factors, or their interaction
struggle for existence in finches
- average rainfall dropped dramatically
- no reproduction during drought year
- 84% of finches died
example of how direction of selection depends on ecology
- droughts in 1977 & 2004
- by 2004, Large Ground Finches had colonized Daphne Major & dominated access to large seeds
- thus, there was selection for smaller beak sizes during the drought
natural selection cannot predict …
the future
in natural selection, every generation reflects …
the impacts of natural selection on the previous generations
natural selection is not _________, & does not lead to __________
progressive, perfection
what does natural selection filter?
it can only filter variation according to fitness in the current population
how can new traits evolve?
natural selection
how does an adaptation evolve?
by increasing the reproductive success of its possessor
reproduction determines …
which genes make it to the next generation
another definition of natural selection
the non-random survival & reproduction of variants randomly generated with respect to need
is natural selection random?
no
how is natural selection not random?
with knowledge about ecology & heritability, evolution by natural selection can be predicted accurately
does natural selection favor a trait for the good of a species? why or why not?
- natural selection never favors a trait for the good of the species
- it can only act on individuals & proceeds without foresight
what can natural selection improve?
the mean fitness of a population
fitness
the extent to which an individual contributes genes to future generations
how to measure fitness
the number of offspring produced by an individual in its lifetime
what is fitness applied to?
phenotypes
how does a camera-like eye evolve?
in vertebrates, the axons of the retinal cells run over the retina & converge into the optic nerve, forming a blind spot
