BILD 3: Evolution and Natural Selection

The three domains of life

Bacteria, Archaea, Eukarya

The three multicellular kingdoms within Eukarya

Plantae, Fungi, Animalia

Branch Point

Most recent common ancestor

What makes hypothesis testable?

it is based on available data and guided by inductive reasoning

What are the two criteria that a hypothesis must meet in order to be a scientific hypothesis?

1. lead to testable predictions by making additional observations or by performing experiments

2. based on observations and assumptions

What are Lyell’s main ideas? What impact did he have on Darwin?

• the same geologic processes are operating today as in the past + at the same rate

• Darwin agreed with this idea which influenced him to believe that Earth must be older than widely-believed few thousand years (not supported by physical evidence); Darwin also brought his book with him on HMS Beagle trip

What are Cuiver’s main ideas? What impact did he have on Darwin?

• extinction is a common occurrence caused by sudden catastrophic events destroying many species living in an area which is then repopulated by other species (saw that older stratum had fossils that looked less like current life-forms & new species would appear while others disappeared)

• Darwin used paleontologists’ work as a source of information

What are Lamarck’s main ideas? What impact did he have on Darwin?

• theory of evolution where (1) body parts used extensively become larger and stronger, and those that weren’t deteriorated and (2) organisms could pass down modified traits to their offsprings; Also that evolution happened because organisms have an innate drive to become more complex

• Darwin also believed that there is variation in the evolutionary process because organisms inherited developed characteristics

What are the two pronciples of Lamarckian evolution? Give an example of how this mechanism was hypothesized to lead to change. Evaluate Lamarck’s views in light of current biological knowledge.

Principles

• Use and disuse—parts of body used extensively become larger and stronger while those unused deteriorate

• Inheritance of acquired characteristics—an organism could pass these modifications to its offspring

Example: Giraffes stretch their necks a lot to reach for tree leaves on high branches→they develop longer necks→this modified trait of longer necks is passed down

Evaluation: wrong on “use and disuse” but right on "inheritance of acquired characteristics”---organisms evolve based on what random mutated traits are advantageous for the conditions of their environment; if it’s heritable, they can be passed down 

Describe the lessons learned from the rock pocket mice studies.

• Mutations are not good or bad, only advantageous or not

• If there is no strong selection pressure for one trait over another, natural selection will not happen for that trait (ex. White bellies for most rock pocket mouse bc visual predators cannot see belly color)

Lineage

direct line of (common) ancestors

Trait

measurable characteristics

convergent evolution

shared traits occur between two species because it evolved multiple times, arising independently in both lineages

Homology

shared traits between two species because both species inherited it from a common shared ancestor

How do you know which traits are homologies in which species on an evolutionary tree with character transitions marked? What about those that are the result of convergent evolution?

• Homologies—when the character transition is marked on a shared lineage line

• Convergent evolution—when the character transition is marked on a lineage line that does not branch off again

What does “descent with modification and divergence" mean?

“Descent with modification and divergence”: evolution with increasing trait changes from species ancestor to species (as they live in various habitats), and increasing (accumulating) differences in traits from other species

• Descent = shared ancestry, resulting in shared characteristics

• Modification = the accumulation of differences

Use the ideas of descent, evolutionary modification, and divergence to explain the patterns of evolution: how lineages change over time on an evolutionary tree

As lineages evolve through time, they tend to:

1. Look more similar to modem species

2. Become more different from one another

3. Become more different from the common ancestor of the group

4. Diversify into more and more species

What is Natural Selection? Is it random?

• based on what traits are advantageous or unadvantageous to survive in the environment (those that don’t have the advantageous trait are less likely to survive/reproduce while those that do are more likely to survive/reproduce)

• only occurs whenever this is variation in a trait that affects survival and/or reproduction

• Yes

What is Mutation? Is it random?

• random changes in dna sequence that create traits that differ from the common traits of the species the organism is from

• Yes

Predict what will happen to the size of a population that has infinite resources available.

Population size will increase rapidly (exponential growth forever)

What factors affect survival?

• Predation

• Starvation (competition or lack of food)

• Emigration

• Habitat loss (e.g., hosing developments)

• Pathogens/parasites

• Fire, flood, drought

What factors affect reproduction?

• Insufficient habitat

• Pollutants

Explain that populations evolve, but individuals do not.

Populations evolve through natural selection over many generations, individuals cannot evolve that way. 

Histogram

Vertical = # of something, Horizontal = category

What are the 3 properties of a trait required for it to be subject to evolution by natural selection? For each property, explain why evolution by natural selection would not happen if that property were absent.

• Affect survival and/or reproduction—if absent, no natural selection would occur (everyone would live)

• Variable—if absent, no natural selection would occur (all the same = none more/less advantageous to survival)

• Heritable—if absent, organisms would not be able to pass on the trait to their offspring (no evolution would occur)

Explain why natural selection only causes evolution if the trait under selection is at least partly heritable.

Evolution happens over multiple generations; if a trait wasn’t partly heritable, the trait cannot be passed down to the next generation & evolution wouldn’t be able to happen

Explain how there can be natural selection without evolution. Explain how there can be evolution without natural selection. Give an example of each process.

• Natural selection w/o evolution: natural selection simply filters which traits survive and which dies, it does not require heritability

  • Ex. If speed, eyesight, limps isn’t heritable 

  • Review what traits aren’t heritable 

• Evolution w/o natural selection: evolution can happen through genetic drift, artificial selection as well

  • Ex. disease kills an amount of a population by random, humans select certain traits for breeding

Define sexual selection.

Sexual selection is how females pick a male to mate with. Usually they go for the males that start out from the others

Explain the evolutionary advantages and disadvantages of brightly colored spots for male guppies.

• Advantage: They more easily catch the attention of female guppies, allowing them to reproduce and spread their color palette of spots. 

• Disadvantage: They are easier to be seen by predators, and more likely to be eaten. 

Predict how male guppy spots will evolve if you put guppies in an environment with many visual predators vs. an environment with few/no visual predators.

• Many visual predators: Guppies will evolve to have smaller spots with less noticeable colors, blending in with the gravel more. This will allow them to live longer as they are less noticeable to predators. (natural selection is more important than sexual)

• Few/No visual predators: Guppies will evolve to have brighter and bigger spots with more iridescent colors and a greater variety of colors. This will allow them to attract the attention of females (sexual selection is more important than natural)