Evolution

Early Earth and EvolutionA THEORY of the origins of the universe

Big Bang

When? -Approx. 13.5 Billion years ago expansion from singularity-MASSIVE AMOUNTS OF ENERGY!-Energy eventually converted to fundamental building blocks of matter.

Evidence?

-Expanding universe-Background radiation-Abundance of Hydrogen

After Big Bang…….

• Stars! – Need hydrogen gas fusion– Form heavier elements– Really big stars go out with a bang supernova!

• Planets!– Leftover “mess” from supernova start to accrete

into larger objects. (NEWTONS LAW!)– Typically these objects will orbit around a start

• SOLAR SYSTEMS!

LIFE!!!!

• Spontaneous Generation.– Theory (hypothesis actually) that life can

randomly emerge from non-living thing

• Biogenesis – Theory that life only comes from pre-existing life.

• Common Ancestor– Theory that every living organism on the planet

is a descendent of an original cell

• Question : Where did first life come from???

Key Experiments• Francisco Redi’s Flies –

–Where do maggots come from

–Bottom Line: no spontaneous generation

Key Experiments• Spallanzani –

–Bacteria in broth come from air? Or other microbes?

–Bottom Line: no spontaneous generation

Key Experiments• Louis Pasteur –

–Bacteria in broth come from air? Or other microbes?

–Key difference from spallanzani?–Bottom Line: no spontaneous generation

Key ExperimentsStanley Miller –

Can we create molecules of life based on conditions of early earth

Put in inorganic gasses

Produced organic amino acids

Questions about the world that started to set the stage for modern evolutionary thought

• GEOLOGY– Age of earth?– Changing earth?

• POPULATIONS– Competition?– Change over time?– Extinction of species?

GEOLOGYHutton and Lyell (geologists)

• James Hutton (1785) – hypothesized earth to be very old when he examined

geologic features such as rock layers and erosion

• Charles Lyell (1833) – Hypothesized that complex geologic processes like

erosion, volcanoes, etc. shaped the earth as we currently see it.

• CONCLUSIONS?????– EARTH IS MAD OLD!– Today’s best guess??? 4.6 Billion Years

How long did this take?????

Early Evolutionists

• Jean-Baptists Lamark (1809)• Recognized that species change over time

• VITALISM – 1809• Change in body structure based

on use/disuse of parts

• Inheritance of acquired characteristics

• Ex. Early giraffes acquired long necks through stretching them to reach leaves in trees.

• Thomas Mathus (1798)

• Observed human population growth will eventually hit a limit due to living space and available food. Darwin would later apply this to all organisms where these limits result in competition.

• Determined this will reach a max due to food and space limitations

• Limited resources in Nature is the basis for what????

• While Lamarck's reasoning behind why change happened was flawed, Lamarck and Malthus both greatly influenced the thinking of Mr. Charles Darwin.

POPULATION GROWTH CURVE

WHERE ARE WE???

Charles Darwin• English scientist born in 1809

• 1831 famous voyage around world on HMS Beagle where he examined numerous different types of animals and the wide diversity of life he found

• Noted that organisms seemed to be uniquely adapted to their environments

• Galapagos Similar organisms on different islands had unique characteristics that suited their specific habitat

On the Origin of Species• Published 1859

• Summarized his ideas on causes of speciation

• Darwin's On the Origin of Species by Means of Natural Selection, made several points that had major impact on nineteenth-century thought:

Darwin and Natural Selection

• Force behind which populations evolve

• Based with the idea that in any given population, there is a amount of variation and not a static/fixed existence

• Based on 3 main principles

1) Competition

2) Survival of the Fittest

3) Descent with Modification

1. Competition

• Members of a species population are in competition with each other for food and space.

• Due to OVERPRODUCTION

• “Struggle for existence”

• Those individuals with traits that give them an advantage make them better competitors.

2. Survival of the Fittest

• Due to the genetic variation in a species, there is phenotypic variation.

• Due to competition, those organisms that have traits which give them a slight advantage over others will survive while those organisms with deleterious traits will die-off

Fitness: ability to survive and pass on ones genes• Those with higher fitness pass on more of their genes to

the next generation Differential Reproduction

• These “strong” genes then increase in frequency

Golly Gee Mr. Darwin, is survival the only thing needed to make you “fit”?

No Billy; survival alone is not enough. An individual who does not reproduce doesn’t contribute to his/her population and therefore doesn’t matter to nature.

3. Descent with Modification• As new favorable characteristics become

established in a population, the species as a whole changes as long periods of time pass.

Does evolutionary change happen in an individual or in a population?

ORIGIN OF SPECIES• Definition of Species – a group of organisms

that naturally interbreed with each other

• Sometimes, two populations diverge (change differently) and become two separate speciesspecies.

• Ex. Hawaiian Honeycreepers– All Hawaiian honeycreepers have similarities in

skeletal and muscle structure that indicate they are closely related.

• Each of the Hawaiian honeycreeper species has a bill specialized for eating certain foods. Scientists suggest that all 23 honeycreeper species apparently arose from a single species that migrated to Hawaii.

Principle of Common Descent• All species (living and extinct) have evolved from common ancestors for a very long time.

• There is strong quantitative support for this theory

• The more dissimilar two organisms are, the further ago their common ancestor lived.

• Fossil Record

• Geographic Distribution

• Transitional Species

• Comparative Anatomy

• Vestigial Organs

• Comparative Embryology

• Comparative Biochemistry

Evidence of Evolution

Fossil Record• Preserved remain of ancient

life in sedimentary rock support change over time.

• Fossils found in lower levels of rock older than ones above. (relative age)

• Majority of species (over 99%) that have existed on this planet are extinct!

• Very hard for an organism to become a fossil.

How is the age of fossils and rocks determined?

• Remains of living things are organic – contain SOME radioactive isotopes of carbon

• Radiometric dating – using half-lives of radioactive isotopes– Radioactive isotopes decay at a constant rate– Half Life length of time for ½ of an isotope to decay

• Ex. Carbon-14 decays to Nitrogen-14• Half-life = 5,730 years• Carbon 14 can only be uses to date fossils less than 50,000 years

old!

Why do we stop taking in carbon 14 when we die?A fossil has 1/8th of the atmospheric ratio of C-14 to C-12. Estimate the age of the fossil.

Geographic Distribution• Biogeography

– study of the distribution of plants and animals throughout the world

1. Some fossils found on different continents are nearly identical - Supports tectonic plate movement

Geographic Distribution

2. Unrelated organisms exposed to same environmental pressures may develop similar traits

• ANALOGOUS STRUCTURES

3. Related species have similar physical anatomy:

– HOMOLOGOUS structures – similar structures, but serve different functions.

Analogous Structures

• Serve similar function but have a much different structure– Ex. Insect wing and bird wing– Ex. Squid eye and human eye– Ex. Whale fin and fish fin

Homologous Structures (Comparative Anatomy)

• Scientists note similarities among physiology of organisms

• Morphologically similar structures that perform different functions are called homologous structures.

Vestigial Organs

• Structures that are of marginal or no use to an organism NOW

Examples of vestigial structures include:

• Skeletons of some snakes retain the vestiges of pelvic girdle and leg bones of walking ancestors.

• Some blind, cave-dwelling fish have eye-sockets but no eyes.

Vestigial

• Human– Appendix– Tailbone

• Lifestyles change. – So do we not need the organ and then it gets

modified OR…do organs get mutated so we find another way to survive.

Comparative Embryology

• closely related organisms go through similar stages during their embryonic development

• “ONTOGENY RECAPITULATES PHYLOGENY!”

Biochemical Similarities

• What we all use– DNA– ATP (energy molecule)– similar enzymes, – same codons for protein synthesis– same 20 amino acids etc.

• Remember, at the cell level we are very close to most other eukaryotic organisms!

Evolution in Action

• All inheritable physical traits that appear in an organisms can be looked at as changes in an organism’s genetics

• Darwin did not understand genetics and therefore could not explain how traits were passed down through generations.

• We now can apply our understanding of genetics and apply them to evolutionary theory.

Phylogeny

• the connections between all groups of organisms as understood by ancestor/descendant relationships.

• Express relationships using a CLADOGRAM

Cladogram

• Gene Pool is combined genetic information of all the members of a particular population

• In a given gene pool, there will typically be two or more different alleles for a given gene.

• Relative Frequency – number of times that an allele occurs in a gene pool compared with the number of times other alleles occur.

• We can oftentimes see that different alleles have different frequencies in different parts of the world. Why do you think this is so?

Ex. Frequency of B allele for blood type

Genetic Change basis of Evolution

• Natural selection acts on phenotypes NOT genotypes, however, this process determines the relative frequencies of alleles.

• Ex. Sickle cell anemia– Phenotype (blood cell shape) because

heterozygous individuals are resistant to malaria.

– Malaria resistance causes sickle-cell allele to be selected for in the population.

Mechanisms of Evolution

• Introduce new Alleles– Sources of Genetic Variation

• Mutations• Sexual Reproduction

• External factors affect the allele frequency

• Remember, it is mutation that proposes and selection that disposes

Natural Selection Single Gene Traits• May result in changes in allele frequencies and

evolution of a population– Allele which increases fitness of organism becomes

more common

– Allele which decreases fitness of an organisms becomes less common and may ultimately disappear altogether.

– Can select for • Homozygotes recessive/dominant (Ex. Tay Sachs)• heterozygote (Ex. Malaria and sickle cell anemia)

Natural Selection Polygenic Traits

• Can affect the distribution of phenotypes in 3 possibly ways– Directional selection individuals at one

end of phenotype range have greater fitness than those in middle or at other end.

– Stabilizing selection individuals in middle of phenotype range have greater fitness

– Disruptive selection Individuals at either end have greater fitness than those in the middle.

Directional Selection• Ex. Pepper Moth (Biston betularia)

• In 1849, a coal-black mutant was found near Manchester, England. Within a century, this black form had increased to 90% of the population in this region.

• What was the selection force?

Stabilizing Selection

• Natural selection often works to weed out individuals at both extremes of a range of phenotypes resulting in the reproductive success of those near the mean. In such cases, the result is to maintain the status quo.

• stabilizing selection is common. In humans, for example, the incidence of infant mortality is higher for very heavy as well as for very light babies.

Disruptive Selection• In some circumstances, individuals at both extremes

of a range of phenotypes are favored over those in the middle

• A hypothetical example of this is where you have a population of rabbits. The color of the rabbits is governed by two co-dominant traits: black fur represented by “B” and white fur represented by “W”. – BB = Black Fur BW = Gray Fur WW = White fur

• Put this population of rabbits into an area that had very dark black rocks as the environment and also near by was an area of very white colored stone. – What phenotypes would have the greatest fitness?

• If these populations were to be cut off from each other thus not being allowed to inter breed it could lead to Speciation.

What can change allele frequencies besides natural selection?

• Genetic Drift– Evolutionary Change can also happen without

natural selection– In large populations, the laws of probability

help predict allele frequencies.– In smaller populations random change in

allele frequency (genetic drift) may occur.– Chance occurrences may increase/decrease

frequency of alleles

Other things that can happen

• Bottleneck – something happens that leaves only a couple of individuals of a population alive

• Founder Effect – whoever colonizes new territory rings only so many alleles

• Migration – new alleles can enter and exit a population via individuals leaving and entering.

Genetic Equilibrium

• In order for there to be no evolution (allele frequencies remain constant) five conditions must be met;– Random mating– Large population– No migration in or out of population– No mutations– No natural selection

• Is this ever the case?

Process of Speciation

• How do new species arise?• Populations must somehow become

reproductively isolated from each other.– Behavioral different behaviors isolate pops.

• Ex. Killer whales may be two different species!

– Geographic pops. geographically isolated• Ex. Albert & Kaibib Squirrel

– Temporal Two pops. reproduce at different times• Ex. Plants and pollen release

Geographic Isolation• Often, when geographic barrier is

removed, the two population can no longer interbreed and now become two species!

Patterns of Evolution

• Macroevolution– Mass extinction– Adaptive radiation– Convergent Evolution– Coevolution– Punctuated Equilibrium

Mass Extinction

– Periodic large-scale extinction events

Mass Extinctions

• There have at least 5 mass extinctions.• Permian – 250 mya, over 90% of marine and

terrestrial species disappeared; maybe due to volcanoes, Pangeae, glaciation

• Cretaceous – 65 mya; ½ marine and many terrestrial forms, including dinosaurs; due to environmental changes or asteroids hitting the earth

Adaptive Radiation

• Single species evolves into several different species that live in different ways (adaptations)

Convergent Evolution• Sometimes non-

closely related organisms will evolve similar characteristics as each are facing similar environmental pressures.

• Australia has numerous species of marsupials with only non-Australian species being the opossum of North America (how did it get there?)

• Many species of marsupials evolved traits similar to mammals on other continents– Ex. Tasmanian Tiger

Co-Evolution

• Due to close relationship two species share with each other, change in one organism results in a change with the other.

• BIG TIME EXAMPLE– FLOWERS AND INSECTS!

TWEEKING DARWINISM

• Traditionally, it was believed that evolution happened in small steps over long period of time. This is called gradualism

• More recently, scientists like Stephen Gould, proposed the idea of punctuated equilibrium which is that a species may remain relatively stable with sudden periods of rapid evolution due to some environmental factor.– CHANGES IN SPURTS!

GEE WHILIKERS!IF EVOLUTION IS ONLY A THEORY, CAN’T IT BE ARGUED THAT IT ISNT SCIENTIFICALLY TRUE?

Theories are nothing to be trifled with. Remember, it holds a lot of power. Evolution is an observable fact (bird beak size changing, antibiotic resistance in bacteria, etc.) but the term theory allows it to grow and develop. For instance, let’s talk about how we have added to our understanding of evolution since my time.

HISTORY TIME!

3.5 billion yearsFirst Single-Celled Organism

• Oldest known fossils are stromatolites, rocklike layers of prokaryotes and sediment.

Figure 26.3 Early (left) and modern (right) prokaryotes

2.7 billion years agoOxygen

Evidence of oxygen accumulation from cyanobacteria in banded iron formations

2.1 billion years agoeukaryotic cells

• Fossils of eukaryotic cells

• Mitochondria and chloroplasts may have originated as prokaryotes engulfed by other prokaryotes in endosymbiosis.

• In serial endosymbiosis, mitochondria probably evolved first

Evidence

• Organelle DNA (similar to bacteria) and independent protein production

• independent reproduction of organelles similar to binary fission occurs during cell mitosis.

• Inner membranes of organelles similar to that of prokaryotic membranes

1.5 billion years agoMulticellular organisms

• Oldest known fossils are algae

• Severe ice ages (Snowball Earth) prevented diversity of eukaryotes for awhile

535 – 525 Cambrian Explosion

• Great diversity of all types of eukaryotes

500 myaMovement onto Land

• Evolved adaptations to live on land and prevent dehydration

• Plants and fungi colonized land together

250 myaFormation of Pangaea

• Destroyed and altered habitats, changed climates, created geographic isolation

• http://www.pbs.org/wgbh/evolution/darwin/origin/

• http://www.micro.utexas.edu/courses/levin/bio304/evolution/speciation.html