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How can we test evolutionary theory?

1. Lab experiments using organisms with short generation times
2. Predicting patterns (in fossil records, in DNA, among living organisms)
3. Long term studies measuring effects of selection in natural environments
4. Manipulating organisms and observing the effects on fitness
5. Computer environments


Why is it wrong to say "just a theory"?

The word theory does not imply that the evidence is weak or uncertain like in general use of word
Ex: theory of gravitation, theory of plate tectonics


Scientific law

Describes how nature acts under certain conditions, without explaining WHY
Ex: Boyle's law


Theory vs Law

Theories are explanations, laws are descriptions
Theories do NOT become laws as evidence accumulates; they are different things


Stages of eye evolution and organisms at that stage

Eye spot (photosensitive)- Euglena
Flat sheet of photosensitive cells
Curved (cup) eye (Directionality of light)- planarian
Pinhole camera eye (blurry image)- nautilus
Jelly lens eye (more focused image)- snail


Most phenotypic traits are (quantitative/qualitative)

Quantitative (exhibit continuous variation)
Influenced by multiple genes


Quantitative traits

Some are determined by a few genes of large effect
Some are determined by many genes of small effect


Is it possible for a new phenotype to arise in a population without any genetic mutations?

Yes, through new combinations of existing alleles


Is a population more likely to shift to another phenotype quickly if the trait is influenced by one gene or multiple genes



Why does it matter that many traits are polygenic?

Adaptations can arise quickly in response to environmental change


Why can adaptations arise quickly in response to environmental change?

1. There is likely to be lots of standing/existing genetic variation in the population (so no need to wait for new mutations since lots of variation is likely to exist already)
2. New combinations of alleles confer new phenotypes
3. Selection acts on multiple loci simultaneously; small changes in allele frequencies at each locus add up to produce large changes in phenotype


Punnett square

Probability of genotypes of offspring within a FAMILY


Assumptions of punnett squares

Random pairing of egg and sperm
No outside egg or sperm
No mutations
Large number of offspring
Equal survival


Assumptions for H-W equilibrium

Random mating
No migration
No mutations
No genetic drift (large population)
No selection (equal probability of death among genotypes)


Levels of selection

Individual/gene level selection
Kin selection


Individual (gene-level) selection

Alleles that facilitate survival/reproduction of the individual increase in frequency


Kin selection

Alleles that cause animals to behave in a way that enhances survival/reproduction of their kin will increase in frequency
Ex: Alarm calls, worker bees, birds


Do animals ever behave in a certain way because it is good for the species?

No, they behave for the good of themselves, not the good of the species


A population in which individuals sacrifice their own reproductive success for the good of the species is vulnerable to invasion by alleles that favor the individual over the species

Because selection favors behavior that maximizes an individual's fitness


How did life begin?

After the earth cooled, there was little free oxygen in the atmosphere and lots of energy available through lightning, volcanoes, and UV light.
Organic molecules could form spontaneously in the oceans


Why do theories change over time? How does the example from classical mechanics illustrate this process?

Theories are testable, meaning that they allow predictions about future observations. If a theory predicts something falsely, that theory can be revised or thrown out for a new theory all together. Classical mechanics was a theory that was added on to over time to include theories about magnetism, gravity, and electricity and how they related to the original classical mechanics theory.


The article indicates that some scientists depend on experiments and others on observational studies. Aren't experiments necessary for a discipline to be considered ‘scientific?’ Are there any branches of science that rely heavily on observational studies rather than manipulative experiments?

The aim of science is to build more accurate and powerful natural explanations of how the universe works — and that requires testing (Links to an external site.)Links to an external site. ideas with evidence (Links to an external site.)Links to an external site. to build scientific arguments (Links to an external site.)Links to an external site.. These arguments form the core of science. Experiments are not necessarily necessary to be "scientific". Both lead to data for scientists to interpret. There are branches such as behavioral biology that rely heavily on observations


How can you make predictions when you are studying events that happened in the past? Doesn’t the word ‘prediction’ imply an expectation of future events, not past events?

Prediction just refers to what someone would expect to see if their hypothesis were correct. It can refer to past, present, or future events.


The article describes hypotheses concerning three past events. What were the predictions that scientists made (and tested) based on these hypotheses?

3. Some 250 million years ago, all the continents we know today were joined together like a jigsaw puzzle. If the continents had been joined together, then the ancient animals that lived on them should have roamed freely across what are now continental coastlines. Thus, where fossilization was likely, we would expect to find corresponding fossils on the coasts of now distant continents. And in fact we do observe this.


Practice: Suppose a scientist hypothesizes that four-legged land animals evolved from fish around 380 million years ago. What prediction could you make to test this hypothesis?

If this hypothesis is correct, then 4-legged animals today should share homologous structures and DNA patterns with the fish from which they were evolved.


You read about the stereotypical image of a scientist. In what ways is this stereotype inaccurate? How do you think this stereotype could be harmful to the process of science?

science is done by unique individuals — not by automated robots coldly following a routine without motivation, ambition, or creativity. Lastly, science is embedded within a global scientific community. Scientists are collaborative with one another. This stereotype of scientists being geeky, loner, socially inept beings is untrue and can lead new scientists to think these false beliefs and may lead people away from the field of science.


Qualitative vs. Quantitative traits

A qualitative trait is one that is either present or not present, and usually does not change in response to the environment. A quantitative trait is one that falls on a continuum, and is usually influenced by many genes.


According to the article, in quantitative traits, the effects of a single gene 'cannot be detected by Mendelian methods.' What does the author mean by this? Why can't they be detected? Do such genes assort according to Mendel's rules, or not?

Mendelian methods assume that one single gene determines a trait. Quantitative traits are often determined by many genes, and so it is hard to estimate phenotypes/genotypes for a change in a single gene. The genes still assort according to Mendel's rules but have a smaller impact on the end result of a trait.


The idea that after a change in the environment, selection may act on standing genetic variation (rather than favoring alleles that arise through new mutation) is a relatively recent area of interest in evolutionary biology. Make sure you understand the difference between those two scenarios. Which one is likely to produce more rapid evolutionary change?

Adaptation from standing genetic variation is likely to lead to faster evolution, because beneficial alleles are immediately available and also because they usually start at higher frequencies. This means that selection acts on the genetic variation that already exists within a population to favor some individuals over others. In the other case, random mutations that arise in some individuals are favored, favoring those individuals.


In the description of adaptive evolution in the fur color of mice, light fur color is likely disadvantageous on the mainland. According to the hypothesis presented in the article, how was standing genetic variation - including alleles that confer light fur color - probably maintained in the mainland population before the mice colonized the islands? Why hadn't alleles for light fur been selected out of the mainland population? Think about this example in the context of the point (made in class) that polygenic traits allow for a high degree of standing genetic variation, and thus facilitate rapid evolution in response to environmental change.

Gene flow from populations experiencing different environmental conditions, or even hybridization with other species, could preserve relatively high amounts of standing variation despite negative selection. Alternatively, alleles that are deleterious under specific environmental or genetic conditions might be hidden from selection because they do not have any effects on phenotype in the ancestral environment. (case for mice)