Day 16 October 19th Chapter 8

8/3/2019 Day 16 October 19th Chapter 8

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At this point

1. I feel like I have a much betterunderstanding of how evolutionworks.

2. I understand that traits are passedfrom parents to offspring, but I dontthink thats evolution.

3. I dont get it at all. I cant see howtraits are passed on from parents tooffspring.


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Survival of the Fittest

q Reproductive success

q Fitness a measure of the relative amount of

reproduction of an individual with a particular

phenotype, as compared with the reproductiveoutput of individuals with alternativephenotypes


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Fruit Fly Example

q One fly carries the genes for a version of atrait that allows it to survive a long timewithout food.

q The other fly has the genes for a differentversion of the trait that allows it to survive

only a short while without food.

q Which fly has the greater fitness?


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The a l l e l e s carried by an individualwith high fitness wil l increase theirmarket share in a population overtime and the population wil l evolve.


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There are three important elements to

an organisms fitness:

1.

An individuals fitness is measuredrelative to other genotypes orphenotypes in the population.


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There are three important elements toan organisms fitness:

2. Fitness depends on the specificenvironment in which the organism lives.


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There are three important elements toan organisms fitness:

3. Fitness depends on an organisms

reproductive success compared to otherorganisms in the population.

If you are sterile, and can never have babies, yourfitness is ZEROOn the other hand, if you inherit an allele that givesyou a trait that causes you to die at half the age ofeveryone else, but also causes you to have twice asmany offspring as the average while you are alive, your

fitness is increased.


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"Survival of the fittest" is amisnomer.Why?


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8.12 Organisms in a population canbecome better matched to theirenvironment through natural selection.


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Take-home message 8.12qAdaptationthe process by which

organisms become better matched to theirenvironment and the specific features that

make an organism more fitoccurs as aresult of natural selection.


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8.13 Natural selection does not leadto perfect organisms.


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Why doesnt natural selectionlead to the productionof perfect organisms?


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Factors that Prevent Populations fromProgressing Inevitably toward Perfection

1. Environments change quickly.

1. Variation is needed as the raw material ofselection.

1. There may be multiple different alleles for atrait, each causing an individual to have thesame fitness.


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8.14 Artificial selection is just aspecial case of natural selection.Apple growers - green, yellow, red, tart, sweet,

large, and small.


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8.15 Natural selection can changethe traits seen in a population inseveral ways.


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Directional SelectionIndividuals with one extreme from the rangeof variation in the population have higher

fitness.

The result of such selection isnot surprising: between 1920

and 1945, average milkproduction increased by about

50% in the United States.Farmers only let the cows with


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Turkeys on poultry farms have such largebreast muscles that they can t get closeenough to each other to mate.

How can such a trait evolve?


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4/28/12 So, could this happen in

nature?

ou ur e s reas s


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ou ur eys w reas sso large that they cannot

mate occur naturally?

1. Yes

1. No


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Stabilizing Selection

Individuals with intermediate phenotypes are most fit.


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22 lbs mom wasdiabetic

Born preemie at 22weeks

Weighed less than 10oz.


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How is medical technology undoingthe work of natural selection inoptimizing the number of babieswith normal birth weights?


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Disruptive SelectionIndividuals with extreme phenotypes experience the

highest fitness, and those with intermediate phenotypeshave the lowest.


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Most mammals do not drink milk after they are weanedbecause they lose the ability to digest lactose. This is

true for about 60% of people. But most people ofnorthern European descent can drink milk (areas wheredairy farming is historically prevalent). What type of

evolution would this exemplify?

1. Directed selection

2. Stabilizing selection

3. Disruptive selection


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Most mammals do not drink milk after they are weanedbecause they lose the ability to digest lactose. This is

true for about 60% of people. But most people ofnorthern European descent can drink milk (areas wheredairy farming is historically prevalent). What type of

evolution would this exemplify?

1. Directed selection

2. Stabilizing selection

3. Disruptive selection

The availability of a reliable source of protein and nutrition hasselected for this trait in those populations that were dairy farmers,but not the rest of the human population. Therefore, the presence

of dairy farming directed the evolution of one trait.


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Based on our discussion so far, what do

you think? Are humans still evolving?

1. Yes

2. No

3. Unsure


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8.16 Natural selection can causethe evolution of complex traitsand behaviors.

Look at thebetta fish!


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4/28/12 1954, William Thompson trained a group of rats to run through a maze fora food reward

H i l if 1% f


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How can a wing evolve if 1% of awing doesnt help an organism fly or

glide at all?


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Often, structuresappear because theyserve some otherpurpose.

Functional Shifts


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Biggest wings hottestregions?


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It is indeed remarkable that this theory

[evolution] has been progressively accepted byresearchers, following a series of discoveries invarious fields of knowledge.

The convergence, neither sought norfabricated, of the results of work that was conductedindependently is in itself a significant argument infavor of this theory.

Pope John Paul II, 1996


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Five primary lines of evidence:

1. The fossil record

1. Biogeography

1. Comparative anatomy and embryology

1. Molecular biology

1. Laboratory and field experiments


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8.17 The fossil recorddocuments the process ofnatural selection.

Although it has been central to much documentation

of the occurrence of evolution, it is a very incompleterecord


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InDarwinstime, it

wasassumedthat thedeeperdown inthe eartha fossilwasfound, the

older itwas.RelativeDating

M b h j


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million years ago

Many branches, not just astraight line


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First found innorthernCanada andestimated at375 millionyears old,Tiktaalik

fossils appearto represent a

transitionalphasebetween fishand land

animals.


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8-18. Geographic patterns ofspecies distributions reflect theirevolutionary histories.


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History Matters

q Who arrived first?

qAre numerous different habitats available?

In Hawaii, it appears that a finch-like

descendant of the honeycreepers arrived4-5 million years ago and rapidly evolvedinto a large number of diverse species.The same process has occurred andcontinues to occur in all locales, not just onislands.


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Day 16 October 19th Chapter 8

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