E volution The Change of Populations over Time

E V O L U T I O NT h e C h a n g e o f P o p u l a t i o n s o v e r T i m e

History

Part 1:

Charles DarwinCharles Darwin

Darwin (1809-1882) was the father of evolution, contributing more to our understanding of evolution than any other individual. He wrote On the Origin of Species, among other works.

HMS Beagle

In 1831, Darwin set sail on the HMS Beagle, from England, to tour the world and collect plant and animal samples. During his voyage, he stopped at the Galapagos islands, where he gathered some of the most important evidence to support his new theory, evolution. Darwin noticed how creatures in the isles were adapted to the specific environment on their island.

Other ScientistsJean-Baptiste

Lamarck

Jean-Baptiste Lamarck was the first scientist to propose a theory of how organisms change over long periods of time. He hypothesized that all organisms have a tendency to complexity and perfection, that body parts could be changed through use or disuse, and that these changes could be passed on to offspring. Lamarck’s theory, while flawed, paved the way for later biologists.

Darwin’s Inspirations

Hutton: Earth was shaped by geological forces over time. Earth was millions of years old.

Malthus: He wrote about the growth of the human population.Darwin’s Peers

Lyell: He argued that Earth’s surface was shaped gradually by processes over many years.Darwin thought that the same gradual change must apply to organisms as well.

Wallace: He proposed a theory of evolution similar to Darwin’s.

Evidence for EvolutionThe Fossil Record

Geographic Distribution

Scientists could document the way organisms have changed over time by comparing living creatures to extinct ones preserved in fossils. Fossils in older (and lower) rock layers predated fossils closer to the surface, the principle of Stratigraphy.

Darwin observed that many organisms with physical similarities were distributed closely geographically, as well. In areas spread apart (such as South America and Australia) with similar environmental conditions, organisms were wildly distinct.

Evidence for EvolutionHomologous Body Structures

Similarities in Embryology

The skeletons of many living vertebrates, while used for varying body parts and purposes, are all constructed out of similar bones (observe the forelimbs of reptiles, birds, and mammals). Compare to Analogous body structures, where body parts with different origins share the same purpose and so resemble each other.

The embryonic developmental stages of many vertebrates closely resemble each other, and develop similarly to make similar cells, tissues, and body parts.

Natural Selection

Part 2:

Natural SelectionNatural selection is a process that affects the distribution of phenotypes in a given population. Organisms that carry certain phenotypes are more or less likely to survive than others, and these organisms pass on genes to their offspring. Natural selection acts only on the phenotype of the organism, but not the genotype.

Natural SelectionDirectional Natural Selection

Directional natural selection consists of selection against one extreme in the spectrum of variance. For examples, giraffes with shorter necks must have been selected against in times of drought, because their shorter necks would have prevented them from effectively seeking out food.

Natural SelectionDisruptive Natural Selection

Disruptive natural selection is the selection against the mean, where the ‘middle’ segment in the spectrum is culled, possibly leading to eventual speciation. An example is beak size in some exotic birds. Smaller, thinner beaks would be able to better consume nectar, whilst larger, thicker, beaks would be able to better crack and eat nuts. The middle-sized beaks, which would be able to do none of these things well, would not benefit their owners.

Natural SelectionStabilizing Natural Selection

Stabilizing natural selection is the selection of both extremes, where only a small, middle, section in the continuum of variance is able to survive easily. This leads to loss of variation in the population. An example is human babies, where infants of abnormally large or small size are unlikely to survive. Infants of medium size are the most viable.

Population Genetics

Part 3:

The Gene PoolThe gene pool is the combined genetic information of all members of a particular population.

It consists of all genes, including all the different alleles present in a population.

The relative frequency of an allele is the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur.

Evolution is any change in the relative frequency of alleles in a population.

Genetic EquilibriumFactors Required for

Equilibrium:

I. There can be no mutationsII. There must be random matingIII. There can be no natural

selectionIV. The population must be very

largeV. There can be no movement into

and out of the population

Population BottleneckA population bottleneck is the drastic reduction of the size of a population (at least 50%) after an event (fire, flood, human interference).

A population bottleneck sometimes causes destruction of genetic variation, leading to an even bigger decrease in the population as the lack of variation allows many of the same species to die to a single event.

Genetic DriftGenetic drift is the random change in allele frequencies that occurs in small populations as a chance event.Genetic drift is one of the basic mechanisms of evolution that relies solely on chance. Some individuals may just happen to leave behind more descendants than others, therefore the genes of the survivors are passed on. Over time, repeated series of this kind of occurrence can cause an allele to become common in a population.

Isolation and Speciation

Types of Isolation:Allopatric: Fancy name for “geographic isolation”. This is when two populations are separated by geographic barriers such as rivers, mountains, or bodies of water. The result of this isolation is the formation of two different gene pools and the lack of genetic exchange.Sympatric: Sympatric speciation does not require large-scale geographic distance to reduce gene flow between parts of a population.

Founder EffectThe Founder Effect is the change in allele frequencies as a result of the migration of a small subgroup of a population.

As a result, the new population may have reduced genetic variation, as there is a smaller number of individuals to contribute to the gene pool.

Questions

Part 4:

1) What is the fossil record?

A. The history of fossils found in human history

B. The number of fossils found for each species that have been discovered by mankind

C. The evidence of life on Earth that shows how organisms change over time

D. How many burgers James ate on Saturday

2) What is a gene pool?A. The number of a single allele in a

populationB. A swimming pool full of genesC. The total number of all genes in a

populationD. How often a gene has a mutation in

a population

3) What are the two main sources of genetic variation?

A. Mutation, genetic engineeringB. Sexual reproduction, mutationC. Asexual reproduction, MutationsD. Crossbreeding, Sexual reproduction

4) What are the three ways natural selection affects the distributions of phenotypes?

A. DirectionalB. SeparatingC. DisruptiveD. All of the aboveE. A and B F. A and C

5) In directional selection, what is the end result?

A. One extreme is favoredB. Both extremes are favoredC. The median of the traits is favoredD. Everything dies

6) List the 5 conditions required to maintain genetic equilibrium.

1:2:3:4:5:

7) What is a homologous structure?

A. A structure that does not have current function but may have been useful to an ancestor

B. Parts that do not have common evolutionary origins but are similar in function

C. Structural features with a common evolutionary origin

8) What is an analogous structure?

A. A structure that does not have current function but may have been useful to an ancestor

B. Parts that do not have common evolutionary origins but are similar in function

C. Structural features with a common evolutionary origin

9) What is a vestigial structure?

A. A structure that does not have current function but may have been useful to an ancestor

B. Parts that do not have common evolutionary origins but are similar in function

C. Structural features with a common evolutionary origin

10) Which type of isolation leads to organisms looking alike but being

different?

A. Geographic IsolationB. Reproductive IsolationC. Behavioral Isolation

Answers

1. C2. C3. B4. D5. A6. • There must be random mating • The population must be very

large• There can be no movement

into or out of the population • No mutations

• No natural selection 7. C8. B9. A10. B

James HuangWritten By:

John DeVitoAria Wiedmann

Rachel Liu