Evolution Review

In the fossil record, transitional fossils linking newer species to older ones are relatively rare. Suggest an explanation for this observation.

According to the model of punctuated equilibrium, in most cases the time during which speciation (that is, the distinguishing evolutionary changes) occurs is relatively short compared with the overall duration of the species' existence. Thus, on the vast geologic time scale of the fossil record, the transition of one species to another seems abrupt, and instances of gradual change in the fossil are rare. Furthermore, some of the changes that transitional species underwent may not be apparent in fossils.

How does sexual recombination produce variation?

A population contains a vast number of possible mating combinations and fertilization brings together the games of individuals with different genetic backgrounds. Sexual reproduction reshuffles alleles into fresh combinations every generation.

Explain why an individual organism cannot be said to evolve.

Although an individual may become modified during it's lifetime through interactions with it's environment, this does not represent evolution. Evolution can be measured only as a change in proportions of heritable variations from generation to generation.

Explain why the following statement is inaccurate: "Anti-HIV drugs have created drug resistance in the virus."

An environmental factor such as a drug does not create new traits such as drug resistance, but rather selects for traits among those that are already present in the population.

How does Darwin's theory account for both the similar mammalian forelimbs with different functions and the similar lifestyle of the two distantly related mammals?

Despite their different functions, the forelimbs of different animals are structurally similar because they all represent modifications of a structure found in the common ancestor. The similarities between the sugar glider and the flying squirrel indicate that similar environments selected for similar environments selected for similar adaptions despite their different ancestry.

Two bird species in a forest are not known to interbreed. One species feeds and mates in the treetops and the other on the ground. But in captivity, the two species can interbreed and produce viable, fertile offspring. Which reproductive barrier most likely keeps these species separate? Explain.

Given the species have different habitat preferences - habit isolation (prezygotic barrier)

Explain how the fossil record can be used to test predictions of evolutionary theory.

If bio geography indicates a particular branching pattern of descent from a single group of ancestral organisms, representatives of the ancestral group should appear earlier in the fossil record than representatives of later organisms. Likewise, the many transitional forms that link ancient organisms to present day species are evidence of descent with modification.

Explain why allopatric speciation would be less likely to occur on an island close to a mainland than on a more isolated island of the same size.

If the is close to the mainland then the organisms and therefore the genepools will not be as separated from each other as the island that is more isolated. The more isolated islands gene pool will be much different from the one on the mainland due to the amount of separation between them which will eliminate the chance that the pools could cross back or mix.

Of all the mutations that occur, why do only a small fraction become widespread in a gene pool?

Most mutations occur in somatic cells that do not produce gametes and so are lost when the organism dies. Of the mutations that do occur in cell lines that produce gamestes, many do not have a phenotypic effect on which natural selection can act. Others have a harmful effect and are thus unlikely to spread in a populations from generation to generation because they decrease the reproductive success of their bearers.

Describe how the following concepts relate to Darwin's theory of evolution by natural selection: over-reproduction of populations, limited resources, and heritable variation.

Species have the potential to produce more offspring than to survive, leading to a struggle for limited resources. Populations exhibit a range of heritable variations, some of which confer advantages to their bearers that make them more likely to leave more offspring than less well-suited individuals. Over time, this natural selection can result in a greater proportion to favorable traits in a population.

How can the Darwinian concept of descent with modification explain the evolution of such complex structures as the vertebrate eye or heart?

Such complex structures do not evolve all at once, but in increments, with natural selection selecting for adaptive variants of the earlier versions.

To what extent are humans living in a technological society exempt from natural selection? Justify your answer.

The people living in a technological society are notably exempt from natural selection. This because living in a technological society allows people to pass on their unfavorable and worthless genes/traits to future generations. "Survival of the fittest" no longer applies because medicine and technology keeps people alive when they would not normally survive on their own. For example, people with type-one diabetes are surviving only because of technology, insulin injections. If there was no technology, those who have insulin-dependent diabetes would not be able to pass on this disease and eventually it would no longer be a threat to the population. Instead of mating and reproducing with the person with the advantageous characteristic, we are reproducing with the individuals who might not be able to hunt for food and instead who we find funny or attractive.

Normal watermelon plants are diploid (2n = 22), but breeders have produced tetraploid (4n = 44) watermelons. If tetraploid plants are hybridized with their diploid relatives, they produce triploid (3n = 33) seeds. These offspring can produce triploid seedless watermelons and can be further propagated by cuttings. Are the diploid and tetraploid watermelon plants different species? Explain.

Yes they are different species because their offspring the triploids cannot produce fertile offspring proving that they are different offspring.