Biology: Evolution Unit

What is a scientific theory?

What is a scientific theory?

an explanatory model that accounts for a large body of evidence; it is more than a hypothesis and it’s considered tentative

What is some of the evidence for evolution?

• fossils of ancient life forms

• genetic analysis

• comparative anatomy

• distribution of living things

What is a mutation? Is it intended or random?

A mutation is a random change in the genetic information that alters genes, which changes the phenotype of an individual, causing new traits that were are not expressed in the genotype of the parents

What are the three kinds of mutations?

• Harmful mutations

  • reduces the reproductive success of an individual and does not accumulate over time in a population

• Beneficial mutations

  • results in a phenotype favoured by natural selection and increases the reproductive success of the individual

  • accumulates over time in a population

• Neutral mutations

  • does not result in an advantage or disadvantage and is the most common

What is artificial selection?

The manipulation of the reproductive success of specific individuals to breed more individuals with desired traits; used to create new breeds or plants and animals; occurs in captivity

What are some of the advantages and disadvantages of selective breeding/artificial selection?

Advantages:

• production of individuals with traits beyond the natural variability seen in the original population (ex: wolves to chihuahuas)

Disadvantages:

• lead to little genetic diversity that makes species susceptible to disease

• favoured traits may be linked to detrimental alleles

• breeders cannot breed for traits that do not already exist in the population

What did people during the times of Aristotle believe about the way animals had been created?

believed that animals and everything on Earth had been created in their present form and were immutable

Explain Buffon’s research and findings

• studied anatomy and compared the structure to the function of various body parts

• noted that some anatomical features have no function (ex: toe that does not touch the ground in pigs and dogs)

• believed that species had been created in a more perfect form but had changed over time

What did Carl Linnaeus and Erasmus Darwin propose?

• both proposed that life changed over time

• Darwin (not Charles) proposed that life might have evolved from a single original source

• LIMITATION: could not explain how living things had changed

Explain Lamarck’s theories + describe the impact of his contributions

• was the first to provide an explanation for how species evolved, though faulty

• proposed two key principles:

  • use and disuse: structures that were used often became larger and stronger while structures that weren’t became smaller and weaker

  • inheritance of acquired traits: individuals could pass on to their offspring traits they acquired over their lifetime

• his contributions proposed important ideas like:

  • all species evolve over time

  • species evolve in response to their environment and become better adapted to that environment

  • changes are passed from generation to generation

How does fossilization work? How old must an individual be to be considered a fossil?

• An individual dies and is buried by sediment, where the lack of oxygen prevents decomposition

  • the pressure causes the deposit to harden and form sedimentary rock, which become mineralized

• Remains must be at least 10 000 years old to be considered a fossil

Explain Cuvier’s findings and theory

Findings:

• simple organisms were found in all layers

• complex organisms were only found in shallow depths

• fossils in shallower depths resembled modern creatures more

• the fossils in deeper layers were simpler than the ones in shallower layers

• rock layers contain many species that did not occur in layers before or after it

Theory:

• did not believe species change over time

• developed the theory of Catastrophism, proposing that the pattern of fossils showed a series of global catastrophes that wiped out most species on Earth

• his theory could not explain the increasing complexity of organisms

Explain Lyell’s theory

• Uniformitarianism: theory that geological changes are slow and gradual (not fast and catastrophic) and that natural laws influencing these changes are constant

• His theory led to the idea that Earth was much older than was previously believed

How many living species are there on Earth?

2 million

What question could Darwin not answer?

How did evolution take place? What physical processes result in it?

What evolved to become the ancient ancestor of all four legged animals?

A fish

What was Darwin’s most important stopping place on his voyage?

The Galapagos Island

What was the standard view during Darwin’s time?

That God had created all creatures perfectly, and they had not changed since then

What important diagram did Darwin create?

The Tree of Life

What master work did Darwin publish?

On the Origin of Species

What happens to fur of mice that live on darker rocks?

It darkens as generations pass

How many genes are in the human genome?

23 000

What percent of DNA makes the stuff of our bodies?

2%

What are genetic switches?

Portions of DNA that turn coding genes off or on or affect their intensity; it results in different gene expression of species that have similar DNA

How much of our DNA is identical to the DNA of a chimp?

99%

What do the unfused plates in a human head allow for?

It allows for the growth of brain into adulthood; it was caused by the loss of a stronger jaw, but some theorize it led to the higher level of intellect humans possess

What is some of the evidence of evolution that Darwin found?

Biogeography, analogous and homologous structures, and vestigial structures

What is biogeography? How does it relate to Darwin’s findings?

The scientific study of the geographic distribution of organisms based on both living species and fossils

• Darwin found that species found on islands resembled those on the nearest land mass

• Closely related species are found in different continents because of continental drift

What did Darwin hypothesize based on his findings in the Galapagos?

He hypothesized that birds, reptiles, insects, and many plants came from the nearest land mass to remote islands, and adapted to the environment; this resulted in new species or variations of a species unique to the island. No mammals, amphibians, and small birds were native to the area because they couldn’t cross the ocean

Explain what homologous, analogous, and vestigial features are, and how they prove evolution

Homologous: structures in different animals that have a common origin but may serve different purposes; proves evolution because it shows that different species have a common ancestor (example: finger bones in whales and humans)

• all early embryos of vertebrates have gills and a tail, showing our earliest common ancestor had these features (probably fish)

Analogous: features that serve the same purpose but developed separately and so have different anatomical structure; prove evolution because they show how species might adapt to environmental pressures similarly (example: bird wings and insect wings)

Vesitigial: features that are no longer useful to a species that are homologous to another species where it’s fully functioning; proves evolution because it shows how species are related to one another and change over time to adapt to the environment (example: goosebumps in humans, toes that do not touch the ground in pigs and dogs)

Explain the role of mutations and environmental pressures in natural selection and evolution

In a population, mutations are constantly arising. If a mutation is beneficial in the environment for the species, it will increase the individual’s reproductive success by either helping it find a partner or being more likely to survive better in its environment to reproduce for a longer time. The individual will pass on the beneficial trait, which will also help its offspring thrive and have an advantage. This is where environmental pressures come in, where those that can keep up with the pressure because they have beneficial traits will thrive, while those that do not will decrease in population or be left behind. Over time, this will lead to a new species arising, because of the rise of new mutations in a species.

What are the four types of natural selection? Describe them

• directional selection: occurs when one extreme of the phenotype is favoured in the environment, leading to a decrease in the population with opposite end of the trait

• stabilizing selection: when the average phenotype is favoured, leading to a decrease in the extremes of the trait

• disruptive selection: when the two extremes of the phenotype are favoured while the average is not, so that population with the average phenotype decreases

• sexual selection: when certain traits are favoured in males finding a mate, producing different phenotypes in males and females (examples: bright colouring, mating rituals, or pleasing smells in plants)

What does each graph represent?

I: stabilizing selection

II: directional selection

III: disruptive selection

What is genetic drift? What is the result? What kind of populations does it affect most?

Genetic drift is a random change in the frequency of alleles unrelated to natural selection; it is often caused by natural disasters, overhunting, or the move to a different environment; it affects small populations most, because it results in the loss of alleles over time, leading to less genetic diversity

What are the two types of genetic drift?

• Bottlenecks: occur after the loss of a large percentage of the population, resulting in only a few surviving alleles; may lead to previously rare alleles becoming more common, or completely being wiped out

• Founder’s effect: when a part of the population moves to a new environment and establishes there; it leads to a change in the frequency of alleles because the new generations would only inherit the alleles of the founding population