Biology Ch. 22-25- Evolution Unit

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Thomas Malthus

- On the Principle of Population
- if the "checks" happened on humans now then it could happen on animals throughout all of history
- introduced idea of "fitness"

Georges Cuvier

- studied how species became extinct
- idea that time could change populations

Charles Lyell

- Principles of Geology
- suggested earth is much older than Bible says
- allowed enough time for theories about evolution to take place


animals which fossils were found, extinct, if god made all creatures equal, how come they died out?

Jean Baptiste-Lamarck

1) life evolves
2) inheritance of acquired traits
3) use and disuse

Darwin brief biography

- comfortable family life
- indecisive about job
- connections get him a gig on HMS Beagle: 5 years, circumnavigated globe

Galapagos Islands

- weird animals: marine iguanas, finches, giant totoises
- a-ha moment

Darwin's later work

sat on work for 20 years, received paper from naturalist who came to same conclusions, quickly published book at same time naturalist published paper

Natural Selection: five devices

1) Overpopulation of offspring (Malthus)
2) Variation among individuals (observation)
3) Competition for limited resources (inference)
4) successful competitors survive, reproduce, and pass on their traits (observation)
5) repeat steps 1-4 for millions of years (Lyell) and life will adapt to the environment

Artificial Selection

- examples provided by Darwin
- just like natural selection except human needs/wants determine fitness
- big changes can happen very fast

Galapagos Finches

- selective pressure of Galapagos islands has driven evolution of finches
- beaks very important, fit for food they ate
- any birds that survive pass on their beaks
- repeated for millions of years

Pesticide Resistance

- life will always adapt if it can
- pesticides kill insects that aren't resistant
- resistant insects reproduce, passing on resistance
- (also occurs with antibiotics and antiviruses)

Modern Science: more research: take home message

natural selection is universal

Common ancestry of life

- fundamental conclusion of natural selection
- " tree thinking" pattern of evolution of life on earth

2 facts demonstrated by common ancestry

- similarity of skeletons of great apes
- similarity between fossils and modern organisms

NeoDarwinism definition

modern theory of evolution (aka the "Modern Synthesis"). Explains evolution in genetic terms

evolution definition

change in genetic characteristics in a population over time- if this is the definition then Natural Selection is not the only way that a population can evolve

Natural Selection:
definition and 3 types

Traits that improve survival or reproduction accumulate in the population. *Selective and adaptive
- predation selection
- physiological selection
- coevolution

Predation Selection

o Acts on both predator and prey
o Examples: camouflage, mimicry, speed, defenses

Physiological Selection

o Acts on body functions/structures
o Examples: disease resistance, physiological efficiency (using oxygen, food, water), biochemical versatility, protection from injury, morphology (anatomy)


o Two or more species reciprocally affect each other's evolution
o Examples: predator-prey, competition, symbiosis

Genetic Drift:
definition and 2 types

Change in the frequency of traits in a population due to chance events. *Random change, not selective, not adaptive
- founder effect
- bottleneck effect

Founder Effect

o A new population is started by a small group of individuals
o Some rare traits may be at high frequency (or "fixed" at 100%); others may be missing (or "lost")

Bottleneck Effect

o When a large population is drastically reduced by a non-selective disaster: famine, natural disaster, loss of habitat
o Loss of variation by change even narrows the gene pool
o Ex: cheetas: now as similar as identical twins, low diversity

Gene Flow:

Change in the frequency of traits in a population due to immigration/emigration. *EQUALIZING CHANGE
ex: overlapping grazing areas of two herds of caribou

effect of discontinued gene flow

Stopping of gene flow > separation of pools > genetic drift > speciation

Sexual Selection:
Why does sexual selection happen?

Change in frequency of traints in population due to gender preferences."The traits that get you mates." *Selective change, may seem maladaptive
Sexually selected traits serve as fitness markers for mating.

sexual dimorphism

- Differences between genders
- Indicative of the effects of sexual selection

Effects of Evolution
How does evolution work?

- Evolution is a population phenomenon
- It emerges from the selection of individuals by the environment.
- Modes of selection- how selection affects a population

3 Modes of Selection

- Disruptive: against the mean, toward both extremes (colors of moths)
- Stabilizing: towards the mean, against extremes (lizards)
- Directional: toward one extreme (giraffe neck lengths)

How Science Works:
The major ways science differs from other modes of thought

Evidence- all ideas are not created scientifically equal. Evidence is required, spectacular claims require spectacular evidence
Falsifiability- scientific thoughts can NEVER BE PROVEN (only supported. Scientific thoughts can be disproven easily (happens all the time)

Hypotheses vs. Theories vs. Laws

- Hypothesis: a testable statement about the universe
- Theory: a major unifying framework, supported by all evidence currently known
- Law: a deduced fact that will always hold true if given certain conditions (not typically used in Biology).

Fossil Record:

• Generally layers of sedimentary rock contain fossils, new layers cover older ones, creating a record over time, fossils can be dated using radioactive decay
• The fossil record show that a succession or organisms have populated Earth throughout a long period of time. Support (proof?) for a VERY old Earth

Transitional Fossils

show evolutionary links between groups of organisms
Ex: Tiktaalik- a transition fossil between fish and amphibians
Ex: Archaeopteryx: Dinosaurs into birds

Anatomical Record: 4 structures

1) Homologous structure
2) Analogous structure
3) Vestigial organs
4) Comparative embryology

Homologous structure

- similarities in characteristics resulting from common ancestry
- similar structure, similar development, different functions
- evidence of close evolutionary relationship (recent common ancestor)
ex: homology in tetrapod limb plan, insect heads, great ape skeletons
- informs phylogeny

Analogous structure

- Similarities in adaptions resulting from similar evolutionary pressures
- Different structures, different development, similar functions
- Evidence of Convergent Evolution
ex: human and octopus eye, wings have evolved multiple times

Vestigial organs

- Structures that serve little or no function
- Remnants of structures that were functional in ancestral species
- Deleterious mutations accumulate in genes for non-critical structures without reducing fitness

Comparative embryology

- Similar embryological development in closely related species
- All vertebrate embryos have similar structures at different states of development

Molecular Biology

• Comparing DNA and protein structure
• Live uses a universal genetic code
• All organisms use DNA as their genetic material
• The code used by ALL ribosomes is universal. A bacteria can make a human protein if given the proper recipe

Building "Family Trees"

- Closely related species (branches) share same line of descent until their divergence from a common ancestor. As this happens, genetic differences accumulate
- Fewer difference in DNA/protein sequences = more recently diverged

Genome sequencing

What can whole genome sequence data tell us about evolution of humans? Primate common ancestry?

Artificial Selection

• Artificial selection (aka "selective breeding") can use variations in populations to create vastly different "breeds" and "varieties"
• This has been used by humans for livestock and crop production since before recorded history
ex: fancy pigeon Pokemon


• The original evidence that informed Darwin and Wallace
• Organisms found in a particular area tend to be more closely related to each other than they are to organisms found in other areas
ex: Marsupials in Australia vs. Placentals in other areas

Observed Evolution examples

• Insecticide and drug resistance- resistant survivors reproduce, resistance is inherited, insecticide becomes less and less effective
• Peppered moths- "industrial melanism"

Only populations evolve.

• Individuals are selected- differential survival, differential reproductive success
• Populations evolve, the genetic makeup of a population changes over time, fitness increases: favorable traits (greater fitness) become more common

Variation definition

• Variation is the raw material for natural selection
• There have to be differences within population. Some individuals must be more fit than others

Where does variation come from?
(2 things)

- Mutation: random changes to DNA (Why?), only way to generate new alleles
- Sex: mixing of genes ("recombination"). New arrangements in every offspring

gene pool

• Gene: determines a trait (ex. Eye color)
• Allele: a variant of a gene (ex. Brown eyes vs. blue eyes), all sexually reproducing organisms have two alleles for each traits
• Population: a localized group of interbreeding individuals
• Gene pool: the collection of alleles within the population, remember the difference between alleles and genes!
• Evolution: change in allele frequencies in a population

5 sources of Evolution

1) mutation
2) gene flow
3) non-random mating
4) genetic drift
5) natural selection

1) Mutation

- Mutation creates variation
- New mutations are constantly appearing
- Mutation changes DNA sequence, changes amino acid sequence, changes protein structure and function, changes traits, changes fitness (maybe)

2) Gene Flow

- Movement of individuals and alleles in and out of populations
- Seed and pollen distribution by wind and insects
- Migration of animals
- Reduces differences between populations
- Gene flow in human population is increasing today thanks to modern travel technology

3) Non-random Mating

sexual selection

4) Genetic Drift

- Effect of chance events; founder effect, bottleneck
- Loss of alleles from gene pool: reduces variation, reduces adaptability

5) Natural Selection

- Differential survival and reproduction due to changing environmental conditions
- Combinations of alleles that provide "fitness" increase in the population
- Adaptive evolutionary change

Hardy-Weinberg variables

Assume 2 alleles = B, b
Frequency of dominant allele (B) = p
Frequency of recessive allele (b) = q

Hardy-Weinberg formulas

Gene pool: p+ q= 1
Individuals: p^2+2pq+q^2 = 1

Frequency of homozygous dominant

q x q = q^2

Frequency of homozygous recessive

p x p = p^2

Frequency of heterozygotes


Speciation: "That mystery of mysteries"

o Darwin never actually tackled how new species arose
o The "Origin of Species" actually has very little to do with the origin of actual species

"Biological species concept"

• defined by Ernst Mayr
• population whose members can interbreed and produce viable, fertile offspring

Other (3) definitions of "species"

Morphological: based on appearance
Ecological: based on niche
Paleological: based on fossils

Speciation = ?

Reproductive Isolation
Species are created by a series of evolutionary processes that result in the reproductive isolation of a population

Allopatric Speciation

o Allopatric = "other country"
o A population is isolated from other populations due to physical, geographic barriers
o If given enough time, and enough evolution, the populations will become reproductively isolated
o What sorts of barriers/events could contribute to allpatric speciation events? (canyons n stuff)

Sympatric Speciation

o Sympatric - "same country"
o The populations remain in the same physical area but become reproductively isolated from other populations due to other mechanisms
o What sorts of events could contribute to sympatric speciation events?

Effects of Speciation

o Isolation of a population does not always result in speciation
o There are several outcomes that can occur following isolation
o Depending on the circumstances, hybrid populations can serve as links between isolated populations
o This is typical of "ring species" like the larus genus of gulls in the Northern hemisphere

Species Barriers
definition and 2 types

- Various mechanisms ("barriers") exist that prevent successful interspecies reproduction. NOTE: "successful reproduction" = productions of fertile offspring.
- We can split these barriers into when they occur in relation to when they occur in fertilization
• Prezygotic barriers: barriers prior to fertilization
• Postzygotic barriers: barriers after fertilization

Examples of barriers w/ no mating attempt

- Habitat isolation- species live in different areas
- Temporal isolation- species breed during different times of day, different seasons, or different years
- Behavioral isolation- unique behavioral patterns and rituals isolate species. Identifies, attracts members of species (ex. Calls, mating dances)

Examples of barriers w/ unsuccessful mating attempt

- Mechanical isolation- reproductive anatomy from one species does not fit with the anatomy from another species
- Gametic isolation- proteins on the surface of gametes do not allow fusion of sperm and egg

Examples of barriers w/ successful mating attempt

- Reduced hybrid viability- hybrid is weak
- Reduced hybrid fertility- hybrid is sterile
- Hybrid breakdown- offspring of hybrid loses hybrid genetic combinations over succeeding generations

Specific speciation examples

- Two different species of antelope squirrel, one for each rim of the grand canyon
- The formation of the Isthmus of Panama has led to the creation of 15 pairs of sibling species in the snapping shrimp genus
- Genetic analysis of the toad population of Europe shows that there is only a narrow zone where hybrids between the yellow-bellied and fire-bellied toads can be found
- Allopatric populations of mice on the island of Madeira demonstrate different chromosomal fusion mutation
- Modern bread wheat is a hybrid species with genetic contributions from three wild wheat grass species

Two modes of thought on rate of speciation

1) Gradualism
2) Punctuated Equilibrium


• Old thinking: Charles Darwin, Charles Lyell
• Gradual divergence over long spans of time
• Big changes occurs as the accumulations of many small ones

Punctuated Equilibrium

• New thinking: Stephen Jan Gould, Niles Eldredge
• Rate of speciation is not constant
• Rapid bursts of change, followed by long periods of little or no change
• species undergo rapid change when they first evolve from parent population

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