Natural selection: 1. In nature organisms struggle to survive
2. There is a large variation
Darwinian fitness (W)
The relative contribution of a particular individual.
It takes survival and reproductive traits into account, this has to be taken into long terms.
Hybrids can be strong but don’t have any reproduction.
Even the gene of the fittest can change a bit over time.
When an organism grows fast the natural selection is faster to.
Testing Darwin’s Four Postulates
1. Individuals within species vary – variation is random and isn’t a respond to the
environment. It isn’t there for the evolvement of the population or the survival of the
population, but only for the individuals survival.
2. Some of these variations are heritable – important because it has to be given to the
offspring. Heritability isn’t perfect so not all the offspring has the traits of their parents.
3. More offspring are produced than can survive.
4. Survival and reproduction are nonrandom – the best fitness will get the most offspring
and you will see more of those beneficial traits. But even though one trait is very good it
doesn’t mean that every seed with this good trait is shown. There are always other factors
that cause death.
Selection (S) = main trait value of selected individuals – trait value of the offspring.
Selection gradient
1. Absolute fitness – 0 = no 1 = yes
2. Calculate the mean fitness of the population
3. Convert absolute fitness to relative fitness – divide absolute fitness by population mean
fitness.
4. Plot relative fitness as a function of trait value.
Selection x heritability = evolutionary response
R = h2 x S
R = response to selection
h = heritability
S = selection differential
The amount of evolutionary change in a population depends on the strength of selection and
the heritability.
Directional selection – directional change in what happens to the fenotype. There is a shift
in the fenotype and sometimes in the variation. The mean changes but the variation doesn’t
have to change!
Stabilizing selection – selection acts against the extremes and keeps the mean at one point.
Reduces the variation without changing the mean.
, Disruptive selection – You get two separate populations, but they still breed so there will be
a mean in the middle. The mean stays the same, but the variants change to the extremes.
You will get two separate means in the end with a small population of the actual mean.
Know the 3 types!!!!!!! EXAM
Describe by drawing the figures and the arrows!!
Adaptation = a feature that, because it increases fitness, has been shaped by NS
Analysis of adaption = show that a trait has been shaped by natural selection
determine the agent of selection.
Identify a adaption
1. Complexity – complex structures are usually adaptive.
2. Engineering – is the trait better for the shape.
3. Convergence – the same shapes by animals that live in the same environment/lifestyle.
Preconditions for natural selection EXAMENSTOF!!!!!!!
1. Variation
2. Heritability across generations
3. Differential survival/reproduction
Pitfalls!
1) The character is the result of historical constraints
2) The character is a byproduct of something else
3) The character is not the product of NS (e.g.: drift)
4) Physical constraints
5) Vestigial traits (no longer functional)
The study of adaptation proceeds in three conceptual stages:
1) Identify the phenotypic variation associated with a trait.
(i.e.: does it vary and can it respond to selection?)
2) Develop a hypothesis of the trait’s function.
3) Test the hypothesis predictions.
A good hypothesis will predict the features of the trait exactly, and the predictions will be
testable.
2. There is a large variation
Darwinian fitness (W)
The relative contribution of a particular individual.
It takes survival and reproductive traits into account, this has to be taken into long terms.
Hybrids can be strong but don’t have any reproduction.
Even the gene of the fittest can change a bit over time.
When an organism grows fast the natural selection is faster to.
Testing Darwin’s Four Postulates
1. Individuals within species vary – variation is random and isn’t a respond to the
environment. It isn’t there for the evolvement of the population or the survival of the
population, but only for the individuals survival.
2. Some of these variations are heritable – important because it has to be given to the
offspring. Heritability isn’t perfect so not all the offspring has the traits of their parents.
3. More offspring are produced than can survive.
4. Survival and reproduction are nonrandom – the best fitness will get the most offspring
and you will see more of those beneficial traits. But even though one trait is very good it
doesn’t mean that every seed with this good trait is shown. There are always other factors
that cause death.
Selection (S) = main trait value of selected individuals – trait value of the offspring.
Selection gradient
1. Absolute fitness – 0 = no 1 = yes
2. Calculate the mean fitness of the population
3. Convert absolute fitness to relative fitness – divide absolute fitness by population mean
fitness.
4. Plot relative fitness as a function of trait value.
Selection x heritability = evolutionary response
R = h2 x S
R = response to selection
h = heritability
S = selection differential
The amount of evolutionary change in a population depends on the strength of selection and
the heritability.
Directional selection – directional change in what happens to the fenotype. There is a shift
in the fenotype and sometimes in the variation. The mean changes but the variation doesn’t
have to change!
Stabilizing selection – selection acts against the extremes and keeps the mean at one point.
Reduces the variation without changing the mean.
, Disruptive selection – You get two separate populations, but they still breed so there will be
a mean in the middle. The mean stays the same, but the variants change to the extremes.
You will get two separate means in the end with a small population of the actual mean.
Know the 3 types!!!!!!! EXAM
Describe by drawing the figures and the arrows!!
Adaptation = a feature that, because it increases fitness, has been shaped by NS
Analysis of adaption = show that a trait has been shaped by natural selection
determine the agent of selection.
Identify a adaption
1. Complexity – complex structures are usually adaptive.
2. Engineering – is the trait better for the shape.
3. Convergence – the same shapes by animals that live in the same environment/lifestyle.
Preconditions for natural selection EXAMENSTOF!!!!!!!
1. Variation
2. Heritability across generations
3. Differential survival/reproduction
Pitfalls!
1) The character is the result of historical constraints
2) The character is a byproduct of something else
3) The character is not the product of NS (e.g.: drift)
4) Physical constraints
5) Vestigial traits (no longer functional)
The study of adaptation proceeds in three conceptual stages:
1) Identify the phenotypic variation associated with a trait.
(i.e.: does it vary and can it respond to selection?)
2) Develop a hypothesis of the trait’s function.
3) Test the hypothesis predictions.
A good hypothesis will predict the features of the trait exactly, and the predictions will be
testable.
