Harold Urey (Uof Chicago chemist) and Stanley Miller (grad student)

 experiment in prebiotic synthesis:

passed electric sparks through mixture, spontaneously formed amino acids

modeled Earth's primordial atmosphere in the lab

theory that life was seeded on Earth from outer space.

-Originated by Anaxagoras (Greek philosopher)

coined the word "panspermia"

discovered why sky is blue

early attempt to answer the question: "Where did the spark of life come from?"

life is an innate property of organic matter

Originated with Epicurus, made popular by Lucretius

Francis Crick and Leslie Orgel

idea that life was intentionally seeded on Earth and other planets by aliens

astronomer, wrote "The Black Cloud", ppopularized the idea of directed panspermia

claimed interstellar dust was teeming with bacteria, seeding life everywhere throughout cosmos

Started the philosophical school of "Natural Theology"

Wrote "Wisdom of God in Creation" (1691)

philosophical school started by John Ray

maintained that every living thing was perfectly adapted to its way of life

fit between form and function in organisms was designed by the creator

natural adaptation and design proved the existence of a wise and benevolent deity

Wrote "Natural Theology" (1802), greatly influenced Darwin

viewed creator as master gardener

also known as "scala natura"

shows the fixed plan behind nature, with man at the top

Swedish botanist set out to reveal divine plan by collecting and classifying plants

believed species were fixed and distinct types, could not evolve or change

 grouped plants together based on reproductive structures

Wrote "Systema Natura", still used by botanists today

invented binomial nomenclature (Genus species) to catalog a closed system of fixed species

wrote "Histoire Naturelle" (1794-1804), a 44 volume encyclopedia of natural history

theorized that each family of animals diverged from common ancestor (common ancestor=specially created)

new species were simply a degenerate version of the created species

ancestral types created, then wandered world and experienced different climates

Theory had two modern ideas:

• Biogeography (geographical distribution) was important in understanding natural history.

• the environment can influence the basic nature of animals.

• Buffon's protégé (asst. in Jardin du Roi), also believed that organisms were shaped by their environment, could evolve

•  theory of Inheritance of Acquired Characteristics

• coined the term invertebrate and BIOLOGY!
• materialist-revived spontaneous generation idea
• thought Chain of Being was an oversimplification

• de Lamarck
• once generated, organisms changed along fixed and parallel paths

• wealthy publisher and an amateur naturalist
• "System of Linear Development"
• "Vestiges of the Natural History of Creation" (1844)
• claimed man descended from lower animals
• evolution continuous and gradual
• still clung to argument from design

• removed man from center of creation
• eliminated Argument from Design as a scientific theory
• eliminated the Chain of Being
• discovered various kinds of finches on the islands off coast of SA
• tortoises started him thinking about evolution (natives could tell by looking at tortoise which island they came from)

• captain of the HMS Beagle
• moody

• wrote "An Essay on the Principle of Population" (1798)
• population wouldincrease geometrically, but resources could only increase arithmetically (growing gap bet. too many ppl and too few resources)
• "the struggle for existence"

• Thomas Malthus
• gap bet.too many ppl and too few resources
• later led to "survival of the fittest", coined by Herbert Spencer

• Charles Darwin- evolution was a selective process
• well adapted individuals would have more offspring than others, passing on their variation to next generation

• Darwin's theory of evolution by Natural Selection:
• Growth with reproduction, inheritance
• variation in populations
• struggle for existence
• natural selection of certain varieties
• change in proportion of those varieties in the next generation
• extinction of poorly adapted forms

• naturalist who almost published the same exact theory as Darwin, even hitting on the same name!
• Darwin presented excerpt of his earlier work at same meeting, establishing priority for his theory

• Darwin's Bulldog, became known as for writing flattering review on "Origin of Species"
• took up debate on Darwin's work since Darwin wa too ill to do it.
• coined term "agnosticism"
• started the journal "Nature"
• founded the "X-Club", secret society of Darwin supporters

• experimented with garden peas, discovered mechanism of heredity
• the physical units of heredity came in pairs, one unit from each parent
• heredity was particulate, not blending of fluids (contrasts Darwin)
• variation was not continuous, but discontinuous.

Blended inheritance/heredity

• gradual and continuous process
• tiny particles

• tiny particles that darwin thought carried the information of heredity
• floated in different parts of the body, knew how to make that body part
• moved to reproductive organs during sex=blended inheritance

• when two similar genes come together (TT)

• split homogenous populations into smaller isolated groups
• local conditions wold shape isolated populations into new species by natural selection

• changes in genetic information
• focused on in "Mendelism"

• "Genetics and the Origin of Species" (1937)
• translated complex models of population genetics into terms field biologists could understand

• species are populations of similar organisms that can interbreed wit one another but are reproductively isolated from other such populations by one or more isolating mechanisms

• each chromatid is a complete strand of DNA, a sequence of genes

• higher organisms have two copies of each chromosome, one from each parent
• contain the same genes at the same loci

• two strands in a coiled helix, each made up of a series of organic compounds called nucleotides

• single strand of nucleotides

• attached to a backbone of sugar and phosphate molecules
• form complementary base pairs:

1. Adenine (A) with Thymine (T)
2. Guanine (G) with Cytosine (C)
3. Uracil (U) substitutes for (T) in RNA

Each of the 20 amino acids is coded for by a sequence of three nucleotides.

• many codons code for the same amino acid, so the system is redundant

• random alterations in genetic information
• minute changes caused by mutations can have a profound effect on organism
• can occur when DNA replicates
• can also occur in chromosomes
• generally negative or neutral, sometimes positive

• organisms with two of each type of chromosome (2N) are called diploid
• advantage of diploid: extra backup copy of DNA, twice the amount of genetic variation!

• reduces th chromosome number of gametes to 1N
• object is to turn one diploid cell into 4 haploid daughter cells (gametes)
• in meiosis, there are 2 complete cell divisions.

• object is to make two identical diploid daughter cells
• chromatids replicate before division
• chromosomes line up at center
• chromatids separate, go to daughter cells
• daughter cells are now identical
• second cell division of meiosis

1. chromosomes line up at center
2. chromatids separate to daughter cells
3. each daughter cell divides into two haploid cels
4. each of four daughter cells now has a single chromatid from each unique chromosome, one complete copy of all the genetic information

• first division in meiosis, turns diploid cell into two haploid cells
• homologous chromosomes line up at the center of the cell
• for a brief time, they are physically joined together (chiasmata)
• one homologous chromosome goes to each daughter cell (random)

• the direction each chromosome takes during reduction division is random

• meiosis shuffles existing variation into infinite new combinations

• During reduction division, homologous chromosomes briefly joined together
• while they are joined, can exchange genes or groups of genes

• if large populations mate randomly, the proportion of two alleles will never change
• evolution is mathematically impossible?
• Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium

• for any two alleles (Aa, let p and q represent the frequency of those alleles (so p2=AA, q2=aa, 2pq=2Aa)
• if all three possible genotypes mate with one another, the next generation will be equal to p2+2pq+q2=1
• gene frequencies will be in equilibrium
• said evolution was mathematically impossible!
• model tells us variation is not enough for evolution

made assumptions:

1. no mutations
2. no immigration or emigration
3. random mating
4. large populations
5. all alleles are adaptively neutral (no selection)

• will always be inequilibrium
• gene frequencies never change over time

• the study of the allele frequency distribution and change under the influence of the four evolutionary processes: natural selection, genetic drift, mutation and gene flow

• transfer of alleles of genes from one population to another
• occurs between local populations
• amount of gene flow depends on dispersal ability

• organisms entering and leaving populations
• consists or neighborhoods
• gene flow occurs bet. local pop.
• amount of gene flow depends on dispersal ability

Inbreeding

• small populations who mate frequently together over time,most likely to cause evolution

• the gene pool of an isolated population will be a random subset of the gene pool of the parent population
• shows that chance events can affect gene frequencies in unexpected ways

• special case of founder effect
• change in allele frequencies in small isolated populations due to random events
• strictly a statistical phenomenon
• best studied for adaptively neutral alleles like blood groups
• one more source of variation that nudges gene frequencies away from the tidy equilibrium of Hardy-Weinberg model

• any factor that acts to reduce or block the flow of genes bet. two populations

1. Geographic isolating mechanisms
2. Reproductive isolating mechanisms

• temporal, mechanical, behavioral, mechanical, ecological

Four kinds:

1. Temporal
2. Mechanical
3. Behavioral
4. Ecological

• population becomes isolated in time
• many species have a fixed breeding season
• shift in timing of breeding could isolate them

• Pinus radiata sheds pollen in February
• Pinus attenuata sheds pollen in April

• changes in behavior, especially courtship and mating behavior
• animals often have complex stereotyped behavior patterns that are under genetic control
• even a small change in courtshipbehavior couldhave a big effect on reproduction
• example: firefly flight patterns (species specific)

• the parts no longer fit together
• could be extreme difference in size
• change in shape of genitalia
• most important in plants (affects polination, change in stigma, shape, or color of petals)

• don't meet, dont mate
• many species have ecological races-specialized to live in a particular habitat
• example: deer mouse Peromyscus has forest race and prairie race
• certain flowers have sun race and shade race
• fleas and other parasites are host-secific

• isolating mechanisms provide barriers to gene flow bet. populations-potential pathways for speciation
• over time, effect of natural selection, genetic drift, mutation, and recombination can become isolating mechanisms
• when isolated population is reunited with parent population, can no longer interbreed. Have become reproductively isolated, can now be considered new species.

Microevolution

• evolution at or below the level of species
• example: the case of the peppered moth, Biston betularia
• until 1845, all known specimens were light-colored moths
• in 1845, a black was captured in Manchester (badly polluted area)
• soot killing off lichens that hid light-colored moths
• industrial melanism

• replacement of a light morph by a dark morph in an industrialized area-nearly 200 species of Lepidoptera

• average value of a trait is shifted in a particular direction (higher or lower)
• the ground finch is a great example
• evolution is NOT progressive

acts to stabilize the population around some average value.

ex: Aristelliger lizards:

• larger lizards better able to defend territory and mate
• larger lizards make a more tempting target for owls/other predators-can't be too large.
• average size human babies have highest survival rate

• the environment selects for the two extremes, against the average, splitting the population in two or more types.

• Demonstrating macroevolution is much harder
• relies on:

1. biodiversity-large number of species, many similar forms
2. biogeography-similar forms in dif. env. shaped by local conditions
3. fossil record-shows pattern of divergence from common ancestors
4. embryology-similarities in early development imply common ancestry (chordate embryos very similar)
5. comparative anatomy-similarities in basic anatomical structure among diverse groups of animals
6. molecular evolution-line of evidence that wasn't known in Darwin's day (amino acid sequence of same proteins in different species show many changes)

• structurally and developmentally similar, even though they may be put to different uses
• derived from common ancestor
• ex: legs of a cat homologous with wings of a bird
• ex: flipper of a whale homologous to human arm
• example of divergent evolution

• superficially simila, but structurally and developmentally different
• evolve because there are a limited number of solutions to evolutionary challenges

1. flight requires wings
2. swimming requires streamlining

• example of convergent evolution

divergence from a common ancestor

Homologous structures are evidence of divergent evolution

• two unrelated lineages converge on a common solution to an evolutionary problem
• analogous structures are evidence of convergent evolution

• theory in evolutionary biology which states that most sexually reproducing species experience little change for most of their geological history, and that when phenotypic evolution does occur, it is localized in rare, rapid events of branching speciation
• S.J. Gould and Niles Eldredge

1. Bacteria
2. Archaea
3. Protista
4. Animalia
5. Plantae
6. Fungi

1. DOMAIN
2. KINGDOM
3. PHYLUM
4. CLASS
5. ORDER
6. FAMILY
7. GENU
8. SPECIES

• current scheme of cassification
• each taxon is a clade, a branch on the tree of life (cladogram)
• only recognizemonophylectic groups
• try to avoid paraphyletic and polyphyletic groups

• each taxon is a clade, a branch on the tree of life (cladogram)
• determined by the traits they share, traits that are different from their ancestors (synapomorphies)

• taxon contains the common ancestor and all of its descendants

• contains common ancestor but only some descendants (most similar)

• contains some descendant species but no common ancestor (may even come from different ancestors)

• Primitive cells, unicellular
• lack a cell nucleus(no nuclear membrane around chromosomes)
• lack cellular organelles enclosed by membranes (no chloroplasts, no mitochondria, etc...)

• multicellular (sometimes unicellular), complex cells
• have nuclei (surrounded by a nuclear membrane)
• may have evolved from endosymbiosis

• very primitive, anaerobic
• produce ~2billion tons of methane/year
• 30% made in bellies of cows, aid in digestion

• ex: cyanobacteria (once called blue green algae)

self-feeder, autotrophic organisms produce their own energy

sunlight (photosynthesis, use H2O)

chemosynthesis (chemical reactions)

chemical reactions

autotrophic bacteria

fed by others, eat other organisms to survive (herbivorous, carnivorous, omnivorous)

can be parasites or saprobes

• get their energy from dead and decaying organic matter
• extracellular digestion-saprobes can secrete enzymes to do the digestion outside the cell

• turn atmospheric nitrogen (N2) into a form that plants can use
• forms nodules on roots of legumes like clover, soybeans, alfalfa

calcareous mound build up of lime-secreting cyanobacteria

earliest known fossils

• heterotrophs
• motile

1. cilia-ciliophora, euglenozoa
2. flagella- dinoflagellata
3. pseudopodia-amoebozoa, foraminifera

• non motile

1. apicomplexa (plasmodium)

protists rely on this

• the passive movement of molecules from area of higher concentration to area of lower concentration
• results from the random movement of molecules

• autotrophs, protists
• photosynthetic
• many referred to as "seaweeds"
• gave rise to higher plants

• temporary protrusion of the surface of an ameboid cell for movement and feeding