Biology 1020 - Lesson 10

Contrast Aristotle's scala naturae to Carolus Linnaeus' classification scheme.

Scala Naturae: Viewed species as unchanging. Recognized certain "affinities" among organisms and concluded that life-forms could be arranged on a ladder, or scale, of increasing complexity. Each form of life, perfect and permanent, had its allotted run on the ladder.Carolus Linnaeus: Adopted a nested classification system, grouping similar species into increasingly general categories. EX: similar species grouped in same genus, similar genera(plural genus) grouped in same family etc. Did not ascribe the resemblances among species to evolutionary kinship, but rather to the pattern of their creation

Summarize and compare Cuvier's, Hutton's, and Lyell's ideas about the significance of fossils to explanations of biological diversity. (ADD)

Gradualism, James Hutton's theory was that earth's geological features could be explained by gradual mechanisms such as valleys forming by rivers wearing through rocks. Charles Lyell's uniformitarianism was based off of gradualism and suggested that mechanisms of change are constant over time. He said that geological mechanisms that happen today are the same as in the past and that they happen at the same rate. Georges Cuvier proposed the idea of catastrophism, stating that events in the past occurred very suddenly and these mechanisms from the past are different from ones today. This idea stated that the catastrophes happened in small regions and the effects were spread by immigration of populations.

Explain the mechanism for evolutionary change proposed by Jean Baptise Lamarck. Explain why modern biology has rejected Lamarck's theories.

Lamarck had the belief that an innate drive to be more complex was responsible for the observed change in organisms. This was later rejected in science due to Darwin's idea of natural selection.

Summarize the mechanism for evolutionary change proposed by Charles Darwin in On the Origin of Species.

The mechanism for evolutionary change proposed by Charles Darwin was "descent with modification." Darwin perceived unity in life, with all organisms related through descent from some unknown ancestor. Over time they accumulated diverse modifications, or adaptations, that fit them to specific ways of life. Natural selection may result in adaptation.

Describe how Darwin's observations on the voyage of the HMS Beagle led him to formulate and support his theory of evolution.

On the HMS Beagle, Darwin observed that different tupes of animals had modifications that made them better suited to their environments. These observations led him to believe that all the animals had come from a common ancestor.

Explain what Darwin meant by "descent with modification".

By "descent with modification," Darwin meant that there is unity in life, with all organisms related though descent from some unknown ancestor. As the descendants of that ancestral organism spilled into various habitats, over millions of years, they accumulated diverse modifications.

Explain what evidence convinced Darwin that species change over time.

Darwin was convinced that species changed over time after seeing population of finches on the Galapagos Islands.

Note how Linnaeus's classification scheme fit Darwin's theory of evolution by natural selection.

Linnaeus - father of taxonomy (names and classification) but believed that species were permanent and never changing.He grouped organisms hierarchically by shared traits, unintentionally created a system for identifying evolutionary kinship.

Describe the two observations and two inferences that lead Darwin to propose natural selection as a mechanism for evolutionary change.From Darwin's observations, what two inferences did he make?

1. Individual's whose inherited traits give them a higher chance of surviving/reproducing leave more offspring than others.2. This unequal ability to survive/reproduce leads to the accumulation of favorable traits in a population over generations.

Describe the three inferences Darwin made from his observations that led him to propose natural selection as a mechanism for evolutionary change.

Inference #1 - production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only of offspring surviving each generation.Inference #2 - individuals who inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.Inference #3 - this unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Explain how an essay by the Rev. Thomas Malthus influenced Charles Darwin.

Darwin realized that the capacity to reproduce was characteristic of all things after reading this essay. The essay was about human suffering (disease, famine, was, etc.) and how it was an inescapable consequence of the human population's potential to increase faster that food supplies and other resources.

Explain why an individual organism cannot evolve.

Natural selection occurs through interactions between individual organisms and their environments. There is little evidence that acquired traits can be inherited by their offspring. Rather, it is the heritable traits that are either amplified or diminished via natural selection.

Explain why natural selection can act only on heritable traits.

If individuals are genetically identical, evolution by natural selection cannot occur

What are three important things to keep in mind about natural selection?

1. individuals do not evolve, populations evolve2. natural selection can only act upon the heritable traits that differ in a population. If individuals are genetically identical, evolution by natural selection cannot occur3. environmental factors vary from place to place, natural selection depends on environment

Describe how natural selection favors the evolution of drug-resistant pathogens.

Drug-resistant pathogens are able to survive despite use of drugs so they are able to pass that trait to offspring

Explain how the fossil record may be used to test our current understanding of evolutionary patterns.

Over time these fossils show that decent with modification produced increasingly large differences among related groups of organisms, resulting in diversity of life.

Explain how the existence of homologous and vestigial structures can be explained by Darwin's theory of natural selection.

Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor. Vestigial structures are remnants or features that served important functions in the organisms ancestors. The existence of these structures are explained by natural selection because they held determine the evolutionary tree from which they came.

Explain how evidence from biogeography supports the theory of evolution by natural selection.

The theory of biogeography supports natural selection because it shows that organisms had the same origin, but adapted to their particular surroundings.

Explain the problem with the statement that Darwinism is "just a theory". Distinguish between the scientific and colloquial use of the word "theory".

Evolution is based on a vast amount of historical evidence.Commonly "theory" is used as scientists use "hypothesis."Darwin's proposed mechanism is theoretical.

Note how gene variability is quantified and explain why nucleotide variability may have limited impact on phenotypic variation.


Explain conditions under which point mutations may be deleterious (i.e., have negative effects), beneficial, or neutral.


Note examples of how chromosomal changes, rapid reproduction, and sexual recombination contribute to genetic variability.


Define the terms population, species and gene pool.

Population - a group of interbreeding individuals of one species that live together in a particular geographic area.Species - a group whose members possess similar anatomical characteristics and have the ability to interbreed.Gene pool - the total sum of genes in a population at any one time.

Write the Hardy-Weinberg equation. State the meaning of the equation, including its terms, in words.

p^2+2pq+q^2=1p+q=1p=frequency of dominant alleleq=frequency of recessive allelep2=frequency of homozygous dominant genotypeq2=frequency of homozygous recessive genotype2pq=frequency of heterozygous genotypes

Explain why meiosis and random fertilization alone will not alter the frequency of alleles or genotypes in a population.

Genes do not actually change, they keep going back into the gene pool.

List the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.

Large population size - genetic drift in small populations can cause genotype frequencies to change over time.No gene flow - migration of individuals or gametes between populations can transfer alleles and change its proportions.No mutations - introduction, loss, or modification of genes will alter the gene pool.Random mating - if individuals pick mates with certain genotypes, or interbreed, the mixing of gametes is not random.No natural selection - differential survival or reproductive success among genotypes will alter their frequencies.

Explain how the Hardy-Weinberg equation can be used for medical applications.


Distinguish between artificial selection and natural selection.

Artificial selection - modification of a species by human intervention so that certain desirable traits are represented in successive generations.Natural selection - process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and submit their genetic characteristics in increasing numbers to succeeding generations.

State the relationship between natural selection and adaptive evolution.


Explain the role of population size in the potential effects of genetic drift.

Genetic drift is effective in small populations and changes the genetic composition of a population by change/random events rather than natural selection. Results in changes in allele frequencies over time.If the population is small, there is less variation between the organisms.If a catastrophe occurs, the population will not be able to recover as quickly because the alleles will not be diverse.

Distinguish between the bottleneck effect and the founder effect.

Bottleneck effect - genetic drifting from the reduction of a population, usually by a sudden change in environment or a natural disaster. Causes the surviving population to no longer genetically represent the original populationFounder effect - when individuals become isolated from a larger population and establish a new population whose gene pol differs from the source population

Summarize the effects of genetic drift on populations.

Genetic drift can result in the loss of rare alleles, and can decrease the size of the gene pool. Genetic drift can also cause a new population to be genetically distinct from its original population, which has led to the hypothesis that genetic drift plays a role in the evolution of new species.

Describe how gene flow can act to reduce genetic differences between adjacent populations.

Gene flow - transfer of alleles in or out of a population of fertile individuals or their gametes.Increases the movement of genes from different populations of species. The more interbreeding between the two populations, the more similar their genes.

Distinguish among directional, stabilizing, and disruptive selection.

Directional selection - natural selection that factors individuals at one end of the phenotypic range.ex: when a population's environment changes or when members migrate to a new habitat.Disruptive selection - natural selection that favors individuals at both extreme ends of the phenotypic range.ex: populations of black-bellied seed crack finches in Cameroon whose members have two distinct beak sizes. Small billed for soft seeds and large birds for hard seeds to crack them. Birds with intermediate sized bills were insufficient for the soft seeds and the hard seeds, have low relative fitness.Stabilizing: _______ex: babies' average weight is around 6 pounds, larger and smaller babies have a higher mortality rate than average babies.

Explain why natural selection consistently leads to adaptive evolution while gene flow and genetic drift do not.

Natural selection allows adaptation in a population by selecting only beneficial alleles. It increases the allele frequencies of heritable traits. The natural selection process decreases deleterious alleles by selecting against them, leading to adaptive evolution.More:

Distinguish between intrasexual selection and intersexual selection and note their consequences for phenotypes.


Describe how frequency-dependent selection and heterozygote advantage can preserve genetic variation at some loci.


List four reasons why natural selection cannot produce perfect organisms.

Natural selection can only edit existing variations.Evolution is limited by historical constraints.Adaptations are often compromised.Chance and natural selection interact