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UCSB ANTH 5 Midterm
Terms in this set (71)
What is the central problem of biology?
Why are organisms so well suited to their environments
Two independent starting points (species or population) that independently evolve similar adaptations in response to similar selection pressures/environments.
How does convergence address the central problem of biology? Explain
Natural selection makes organisms well adapted to their environments. Convergence is
evidence of this process; that two organisms can have the same adaptive solution even coming
from different starting points shows that selection works to adapt organisms in relation to
The indigenous distribution of human skin color in the Old World (Africa, Europe, and Asia) and the New World (the Americas) is a good example of convergence. Explain the selection pressure(s) underlying this convergence
The selection pressure is the tradeoff between vitamin D synthesis, which requires some UVb radiation, and skin cancer, which is the result of too much UVb. Individuals close to the
equator, at lower latitudes, will have darker skin (more melanin) to protect against skin cancer;
individuals at higher latitudes will have lighter skin (less melanin) to enable sufficient vitamin D synthesis. The convergence is around darker skin colors at lower latitudes; New World populations independently evolved this
What is a species? How can you decide if you're looking at two populations of a single, or two species?
A species is a set of populations of individuals who can interbreed/who share a gene pool.
If the members can interbreed, they are two populations of one species. If the members can't interbreed, they are two species.
Our current understanding of speciation depends on two ideas, uniformitarianism and gradualism. In two sentences, one for each concept, specify how each of these is relevant to speciation
Uniformitarianism: requires that the processes that account for speciation are observable and measurable. The processes accounting for speciation are constant throughout time and space.
Gradualism: requires that there not be major gaps between species because no mother has ever birthed an offspring that didn't belong to the same species. Small changes add up to large changes that create new species OR microevolution leads to macroevolution and new species.
Explain how ring species support or undermine the uniformitarian and gradualist model of speciation. To answer adequately you will need to say what a ring species is
A ring species is a collection of populations where adjacent populations can
interbreed but the end populations can't interbreed.
Uniformitarianism: Around the ring, selection is fitting populations to their
Gradualism: Species level differences are no different from the addition of many
The goal of science is to-
explain reality (the universe) with the fewest and most credible assumptions.
Evolution by natural selection is
the differential perpetuation of alternative replicating entities.
Phenotypes (phenotypic traits)
are the strategies of genes for getting perpetuated.
Some examples of strategies:
Assembling a camouflage appearance.
Supporting efficient foraging and digestion
Inducing altruism when rb>c
Cheating during meiosis
Positive fitness effects in one sex that outweigh negative effects in the other.
Producing mating advantages that outweigh associated survival costs.
Evolution by natural selection has two components:
1) The production of variation (mutation) which is random (with respect to adaptation).
-Meaning that, simply because a new allele would be helpful, doesn't make it more likely to occur.
2)The sorting of variation (selection) which is highly non-random (with respect to adaptation).
-Meaning if it's good at getting into the next generation, it will.
Mutations are usually harmful...
since phenotypes are already very well adapted (highly anti-entropic) because of a history of past selection.
Therefore a change is likely to make things worse.
Mutation does not produce adaptation.
Selection favors only a small proportion of mutations (the fortuitously helpful ones).
Evolution is gradual meaning that:
1) Mutations of small phenotypic effect are most likely to be favored.
2) Every offspring belonged to the same species as its parents.
3) In a perfectly complete fossil record it would be impossible to recognize species boundaries (the stadium analogy).
While selection is powerful it cannot plan for the future, hence:
1) No new mutation will be favored unless it provides an immediate benefit.
2) If the present is different from the past, adaptations designed in the past will be imperfect.
If it's difficult, you're not designed to do it. If it's easy, you are. Adaptations feel effortless.
If selections is so powerful, then why aren't we perfect?
We are designed for a different time and place.
What causes similarity between organisms? (2)
1. Shared ancestry
What does convergence do?
Convergence makes distantly related forms similar
What is convergence?
Refers to any case where similar adaptive outcomes arise independently, where evolution seems to have produced the same results more than once. Organisms not closely related independently evolve similar traits as a result of having to adapt to a certain environment.
What is divergence?
Different adaptive outcomes arise based on a similar ancestry from a shared starting point (can interbreed so still of same species). The accumulation of different traits between groups can lead to a new species, especially when the same species is separated and the gene flow changes until there is a differentiation of characteristics between the groups.
Would selection ever delete a trait after having created it?
Yes, if it is too costly.
To an evolutionist, what is altruism, and why is it a puzzle?
When the cost to me benefits someone else.
It's like a puzzle because if we know WHAT people are doing then the question becomes WHY.
How many times did full trichromatic vision evolve in primates?
Two. Natural selection twice solved the problem of getting three different retinal pigments into both male and female primates: once in the common ancestors of all apes and Old World monkeys, and a second time in the ancestor of howler monkeys.
In reciprocity who/what benefits from the altruism?
The benefit of the receiver has to be larger than the cost to the donor.
In kin selection who/what benefits from the altruism?
The relatives of the organism.
Why do critics of evolution by natural selection think that complex traits like the eye are a threat to the theory?
They argue that for an eye to function properly all of the components must be present and wired perfectly in order for the eye to work properly. However, no single mutation could be expected to produce all of those elements, much less integrated in the right way. Thus, natural selection could not have created the eye.
The vertebrate eye is a classic example of a complex adaptation. What evidence do evolutionists say in response?
They discuss how there are creatures that have sheets of light sensitive material; eyes similar to that of humans, etc. The presumption would be that each type of eye is useful to the creature otherwise they wouldn't possess it. They use mollusks and squids who possess eyesight better than humans as an example.
Does the rapid evolution of lizard anatomy contradict the concept of gradualism? Why or why not? (What does gradualism imply about rates of evolutionary change?)
It SUPPORTS as the reproductive rate gradualism still exists it's just the rate in which it's occurring. The change was also small gradualism says small changes are better. Rate of evolution= strength of selection pressure and reproductive time of species.
What is gradualism (what does it claim)?
The idea that the changes that are incorporated over evolutionary time are small changes. Motions of small effect are more likely to be helpful than mutations of large effect.
What do ring species suggest about the relationship between micro and macro evolution; what perspectives do they support?
Micro can add up to macroevolution changes and ring species are a great observable example.
Give an example of an obligate trait
Sweating/shedding to better regulate heat
Pupils dilating and contracting b/c of different types of light
What is susceptibility, and does it differ from a facultative trait? Explain.
Key difference is that it's acted on by the environment but doesn't respond to it. Ex: Too much UV we can't immediately build up melanin on the spot thus you burn.
What is heritability?
Variability in a phenotype in a particular trait in a given population.
Can races be objectively identified in the same way that species can?
No, because unlike species which can be recognized by reproductive isolation, race has no clear boundaries.
4 Characteristics of Life
Organized, Complex, Adjusted, Reproduces
Darwin and Wallace
Developed theory of evolution
Founder of demography; developed first 3 steps of natural selection argument
Six-Step Natural Selection Argument
1. Reproduction is exponential
2. Numbers of organisms tend to be relatively stable in nature
3. Many individuals must fail to reproduce
4. Individuals with more advantageous traits are more likely to survive and reproduce (natural selection)
5. Offspring resemble their parents
6. Advantageous traits become more common over the generations
What constitutes an advantageous trait?
It promotes reproduction
Similar structures in different organisms
Generation by generation changes in gene frequency
large scale changes in a species over geological time
The processes that shape the world are always the same
The changes that are incorporated over evolutionary time are small changes
What kind of mutation is most likely to be favored?
A Small mutation
The evolutionary process by which new biological species arise.
Causes of Speciation
Any factors that discourage gene flow
A ring species is a situation in which two populations which do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed.
Traits that adapt based changes in the environment (ie Skin Color, Pupils Dialating)
Traits that develop and don't change based on the environment
A failure for a facultative trait to respond to the environment in time
True or False: Mutations are just as likely to be beneficial as they are to be harmful.
False: They are most likely to be harmful.
2 Limits on spreading advantageous traits
1. Every trait has associated costs. A trait must produce net positive reproductive effects.
2. A trait must be transmitted reliably from parent to offspring, or selection won't be able to spread it.
Adults are _____
Gametes are _____
The genes itself
The outward expression of those genes
variant of a gene
Two Matching Alleles
Two Different Alleles
Expressed only when Homozygous
Expressed even when Heterozygous
Linear aggregation of genes
Place on a chromosome where genes for a particular trait occur.
How genes specify the recipes for proteins
A type of mutation that causes a single nucleotide base change, insertion, or deletion of the genetic material, DNA or RNA
Natural selection ____ to spread any favorable new alternative that arises by chance.
Tends, a trait can be lost by chance and not spread even if it's favorable.
The change of allele frequency in a population due to random chance.
Closely related organisms differ
The idea that selection favors what's good for the group as a whole
The idea that an organism is altruistic towards their kin
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