Evolution Unit 9

What is evolution?  Evolution: A change in genes of a population over time.  The Theory of Evolution: Life has changed over time

Early Concepts of Evolution - Lamarck  Theory of Use and Disuse: organisms could pass on acquired characteristics  Any physical alterations that make an organism better suited to its environment will be passed on to its offspring  ex) giraffes gradually stretch necks over lifetime, pass on stretched necks to offspring  Discarded due to lack of evidence

Charles Darwin  Served as naturalist on the voyage of the HMS Beagle,  Collected specimens from the Galapagos Islands – a set of (relatively) young volcanic islands off the coast of Ecuador

Creatures of the Galapagos

Charles Darwin  Published his book, On the Origin of Species in1859  Proposed Theory of Natural Selection

Theory of Natural Selection  Variation: Random differences between individuals in a population.  Struggle for Existence: More individuals are born than can survive  Survival of the Fittest: Individuals with favorable variations are more likely to survive and reproduce  Descent with Modification: Because the most “fit” organisms have more offspring each generation, the population will become better adapted over time.  This is how populations adapt to environments over long periods of time.

Theory of Natural Selection  Natural Selection is the driving force behind Evolution.  Important!  Evolution only selects the fittest traits that arose through random variation (mutations and sexual reproduction)  Organisms can’t evolve because they need to change! Evolution only acts on what is already there.  Words to avoid when talking about adaptations: “need”, “want”, “try”, “had to”, etc…

Is what’s best for reproduction always what’s best for survival?  If they’re at odds – which one is more important?  Sexual selection: traits selected for mating success Click for videos

Macroevolution

Speciation  Speciation: the formation of new species.  Members of populations stop interbreeding (called reproductive isolation). Over time, populations change independently of each other until they are different species.  Allopatric Speciation  Populations become geographically isolated by a physical barrier.  Sympatric Speciation  Populations become behaviorally isolated and no longer mate (different mating behaviors or times, chromosomes)

Rates of Evolution: Two Models  Gradualism: Evolution occurs in small, gradual steps over time.  Punctuated equilibrium: Evolution occurs in bursts of speciation followed by long periods of time unchanged (equilibrium).

Types of evolution  Divergent evolution: 1 species separates into 2 species.  Adaptive radiation: many species evolve from one common ancestor

Types of evolution  Convergent evolution: two distantly related species evolve similar traits  Creates analogous structures

Types of Evolution  Co-evolution: Species strongly affecting each other’s evolution  Likely to happen when different species have close ecological interactions with one another:  Predator/prey, Parasite/host, Pollinator/flower 1862: Darwin observed the Madagascar Orchid and predicted that an insect species must exist with a proboscis (tongue) long enough to reach the nectar

Co-Evolution  1903: Species of hawk moth discovered  It must back up over a foot from the orchid to unroll its proboscis.

Evidence for Evolution

What is the scientific evidence for evolution? 1.Fossils 2.Homologous Structures 3.Vestigial Structures 4.Embryo Development 5.Molecular Evidence 6.Real-time observations

#1: Fossils  A fossil is evidence of an organism that lived long ago. Scientists have used the fossil record to construct a history of life on Earth.  Scientists have found “missing links” that have traits of two different classes of organisms  EX: Archaeopteryx— had traits of reptiles and birds

Dating Fossils  Fossils are usually found in sedimentary rock. Hard body parts (shells, bones) become fossilized when minerals replace tissue over time.  Relative Dating  Law of Superposition – new layers of rock are deposited on top of older ones.  Older fossils are found deeper than newer fossils.

Dating Fossils  Radioactive Dating  Also called absolute dating because it gives the actual age of fossils.  Calculates age by examining the amount of a radioactive element remains in a fossil.  Half-life: how long it takes for half the atoms of a radioactive element in a sample to decay. These are known for many elements, so can be used to calculate the age of a fossil.

#2: Homologous Structures  Features with similar underlying structures, inherited from a common ancestor  May have adapted for different functions over time.  Ex) Forearms of mammals – bat wing, whale flipper, cat paw

Analogous Structures  Do NOT show recent common ancestry  Structures that independently evolved to perform the same function.  Will have different underlying structures.  Ex) insect wing, bat wing, bird wing

Homologous or Analogous?

#3: Vestigial Structures  “Vestiges” = left over  Structures that appear to have no function, but were once useful to an ancestor  Examples  Appendix, tail bone, goose bumps and body hair  Snake limb bones  Dandelion flower parts

#4: Embryo Development  More related species have similar embryo development  Human embryos contain gill arches and tails – features that disappear during development

Species Parings # of Amino Acid Differences Fruit fly - dogfish shark26 Fruit fly - pigeon25 Fruit fly - screwworm fly2 Fruit fly - silkworm moth15 Fruit fly - tobacco horn worm moth14 Fruit fly - wheat47 #5: Molecular Evidence (Genes)  All living things have DNA with the same 4 bases and many shared proteins  The more similar the genes, the closer ancestry of organisms

#6: Real-Time observations  Rock Pocket Mice, Peppered Moths  Antibiotic and Pesticide Resistance  These are instances of evolution by natural selection occurring right before our eyes – and some with very real consequences for us.  Why can bacteria and pests (insects, weeds) evolve so rapidly?

Antibiotic Resistance 1. A few bacteria in a population happen to carry a gene that allows them to be resistant to an antibiotic 2. After treated with antibiotic, most normal bacteria die 3. The resistant bacteria multiply 4. Eventually the entire infection evolves into a resistant strain (which can be passed to others) This happens quickly because bacteria reproduce quickly – many generations in short period of time.