Post on 02-Apr-2015
Evolution Evolution
Satirical cartoon by Thomas Nast, from Harper’s Weekly, August 19, 1871.
ObjectivesObjectivesDefine evolution.Outline the evidence for evolution.State that populations tend to produce more
offspring than the environment can support.Explain that a consequence of over-reproduction
of offspring is a struggle for survival.State that members of a species show variation.Explain how sexual reproduction promotes
variation in a species.Explain how natural selection leads to evolution.Explain two examples of evolution in response to
environmental change.
Charles DarwinCharles DarwinBritish; lived from 1809 to 1882.Began to develop the theory of
evolution on a trip around the world aboard the HMS
Beagle.
Charles DarwinCharles DarwinCame to realize that the earth had
changed over a long period of time, which caused
some crea- tures to go extinct, opening up space for new creatures to appear.
The history of life on earth wassimilar to a branching tree, tracing back to some common ancestor. Nature selected which creatures survived and passed on their characteristics. Species change!
Evolution definedEvolution definedEvolution: the change over
time in the frequency of inherited variations in a
population over generations.
Natural selection amplifies or diminishes inherited (not acquired)
variations.
Evolution definedEvolution definedEvolution: the change over time in the
frequency of in-herited variations in a population (not individuals).
Evolution definedEvolution definedLamarckian vs. Darwinian evolution: change over time
Lamarck was a Frenchman who lived before Darwin and first proposed creatures change over time (evolve).Example: giraffes have a long neck because one stretched its neck to reach high branches and passed the trait on.
Evolution definedEvolution definedLamarckian vs. Darwinian evolution: change over time
Darwin would say that giraffe’s necks come in various sizes. Those with a longer neck can reach higher branches and survive better during hard times and pass the trait on to their offspring.
Evolution definedEvolution definedLamarckian vs. Darwinian evolution: change over time
Common errors“Potato beetles evolved resistance to DDT in order to survive.”
There is no intention to evolve.The beetles either had or didn’t have the genes needed to
survive the chemical.Offspring of the survivors shifted the population toward a greater likeli- hood of resistance overall.Peppered moths come in various colors, white to black. Population colors shift as colors of tree trunks change over time, and pre- dators choose different colored moths..
Natural selectionNatural selectionNatural selection: the differential success in the
reproduction of different phenotypes resulting from the interaction of organisms with their environment.
Charles Darwin’s mechanism of evolution.Developed from 5 observations:
1) Species are so fertile that populations would rise exponen- tially if all individuals reproduced successfully.
2) Populations tend to remain stable in size, except for seasonal fluctuations.
3) Environmental resources are limited.4) Individuals of a population vary; no two
individuals are exactly alike.5) Much of this variation is heritable.
Natural selectionNatural selectionHow natural selection works:
Populations tend to produce more offspring than the environment can support.
As a consequence, overproduction of offspring leads to a struggle for existence, with only a fraction of the offspring surviving each generation.
A generation of mice lasts 45 days, then there are 4 – 7 babies. After 45 days there are perhaps 25 mice, then
after another 45 days there could be 125, then
625.
Natural selectionNatural selectionHow natural selection works:
Individuals in a species vary.
Natural selectionNatural selectionHow natural selection works:
Sexual reproduction promotes variation in a species.
Genes are redistributed and mixed among individuals.Asexual reproduction would produce no differences.
Natural selectionNatural selectionNatural selection leads to evolution
Survival is not random, but depends in part on the hereditary make-up of the individuals.
Individuals more fit in their environment are likely to leave more offspring than those less fit.
Preferential survival & reproduction leads to a gradual change in a population, with favorable characteristics accumulating over the generations.
Examples of natural selectionExamples of natural selectionEvolution of resistance to in-
secticides in insect species.Effectiveness of insecticide
decreases with time.Each generation there are
more resistant insects.Natural selection edits
existing variation.Natural selection favors
characteristics that fit the current, local environment.
Examples of natural selectionExamples of natural selectionDrug-resistant strains of HIV evolve rapidly in
the viral population infecting any particular patient.
Like pesticide resistance: the drug 3TC interferes with HIV replication in human cells. Resistant strains become 100% of the population in just a few weeks.Bacterial resistance
to antibiotic drugs works in the same
way.
Evolution Evolution
Satirical cartoon by Thomas Nast, from Harper’s Weekly, August 19, 1871.
Evidence for evolutionEvidence for evolutionEvidence of evolution is everywhere in biology.
Fossil recordHomologous structuresBiogeographyEmbryonic developmentMolecular biology Selective breedingNatural selection
within human lifespan
Evidence for evolutionEvidence for evolutionFossil record
Fossils are “any traces of dead organisms”: bones, tracks (foot-prints), leaf impressions, excrement, actual organisms frozen in ice, in amber, or in tarpits.
Evidence for evolutionEvidence for evolutionFossil record
Most fossils are found in sedimentary rock where deeper rock is older, formed from sand or clay deposits.
Stratigraphy – dating fossils by charting the rock layers.
Since the late 1940s, fossils are dated by the decay of
radioactive isotopes. This is called radiometric
dating.
Evidence for evolutionEvidence for evolutionFossil record
The fossil record in rocks provides relative ages.Radiometric dating can
determine absolute ages. Organisms accumulate radio-
active isotopes when alive. Isotopes decline after death
- they decay (transform) into another element.
Most carbon is 12C, but there is a small yet constant amount of 14C in the air, and therefore in our living bodies – 1 part per trillion.This amount declines after death.
Most carbon is 12C, but there is a small yet constant amount of 14C in the air, and therefore in our living bodies – 1 part per trillion.This amount declines after death.
Evidence for evolutionEvidence for evolutionHalf-lifeHalf-life: time for ½ of the isotope atoms to
decay.Use 40K to date old rocks: half-life = 1.3 billion yr.Use 235U for early vertebrates: half-life = 700 mil. yr.Use 14C for recent fossils: half-life = 5,730 years.
Evidence for evolutionEvidence for evolutionUsing 14C dating to determine the age of organic
materials. Half-life of Half-life of 1414C is 5,730 years.C is 5,730 years.
Work backward from the amount present today toa time when there was maximum 14C,1 part per trillion.
Evidence for evolutionEvidence for evolutionFossil record
Fossils give evidence about the major branches of descent in the tree of life.
Order establishedEx: fossil fishes predate other
vertebrates; amphibians are
next, followed by reptiles, then mammals and
birds.
Evidence for evolutionEvidence for evolutionFossil record
Transitional forms link old & new species.
Evolution of horse’s hooves from 5 toes.
Evolution of whale from horse-like animal: whale
retains a pelvis where hind legs
once attached; forelegs now flippers
Evidence for evolutionEvidence for evolutionHomologous structures
Features of new species are altered versions of ancestral features. Similarity in characteristics resulting from common ancestry is known as homology.
All cats have a common ancestor.All cats have a common ancestor.
Evidence for evolutionEvidence for evolutionHomologous structures
For example, the forelimbs of human, cats, whales, and bats share the same skeletal elements, but different functions because they diverged from the ancestral tetrapod forelimb.They are homologous structures.
Evidence for evolutionEvidence for evolutionVestigial organs are homologous structures that
have marginal, if any, importance to a current organism, but which had important functions in ancestors.
Skeletons of some snakes & fossil whales retain vestiges of pelvis and leg bones of walking ancestors.In humans - wisdom teeth, tailbone, appendix.
Evidence for evolutionEvidence for evolutionBiogeography - the study of the distribution of
life forms over geographical areas. If evolution is true, then we should expect to find
related species living near each other Except in cases of great mobility (like sea animals, birds, and animals distributed by humans) or over long periods of time (due to plate tectonics).
If, however, we find that species are distributed in a random geographic manner, with closely related species no more likely to be found close to each other than unrelated species, then this would be strong evidence against evolution and common descent.
Evidence for evolutionEvidence for evolutionBiogeography
Plate tectonics – the continents are on plates that glide over the surface of the earth carrying life with them.
Evidence for evolutionEvidence for evolutionBiogeography
Identical fossils in parts of the world now widely separated indicate that the continents were once joined.
The southern part of Pangaea
Evidence for evolutionEvidence for evolutionBiogeography
Australian example: marsupials vary widely but are more closely relat-
ed to each other than to similarly-
appearing animals on other continents.
All have a pouch!Placental predators
out-competed them on
other continents, and they disappeared. Australia (with no placentals) was isolated.
Evidence for evolutionEvidence for evolutionBiogeography
Marsupials ori-ginated in SA
70 million yrs ago then spread
to Australia.
Evidence for evolutionEvidence for evolutionBiogeography
Species tend to be more closely related to other species from the same area than to other species with the same way of life, but living in different areas.
The sugar glider from Australiais more closely related to othermarsupial mammals in Australiathan to the flying squirrel, a pla-cental mammal of North America.This is an example of convergentevolution.
Evidence for evolutionEvidence for evolutionEmbryonic development
Genes for embryonic development are conserved in many different species making the embryos similar.All vertebrate embryos have structures called pharyngeal pouches in their throat at some stage in their development. These develop into different, but still homologous, adult structures: gills of fish or Eustachian tubes in mammals.
Evidence for evolutionEvidence for evolutionMolecular biology corroborates
evolutionary trees.Evolutionary relationships among species are documented
in their DNA and proteins.Ex: the Cytochrome c protein
is more similar when crea-tures are closely related:
Human & chimp have the same 104 amino acids,
dog has 13 differences, rattle- snake has 20 changes.
Evidence for evolutionEvidence for evolutionSelective breeding
Humans have domes- ticated many animals,
giving them new char- acteristics over
time (they evolved).
Dogs domesticated from wolves about
15,000 years ago.Sheep, cattle, horses
goats, pigs, chickens
Evidence for evolutionEvidence for evolutionSelective breeding
Plants: corn, wheat, potato, bean, cabbage, etc.