Natural Selection

evolution.berkeley.edu/evosite/misconceps

*Charles Darwin (1809-1882)

Naturalist aboard HMS Beagle Collected living specimens & fossils Visited Galapagos Islands (p.394, fig. 15.1)

Tortoises Finches Marine iguanas

Bred pigeons – artificial selection

http://nayagam.files.wordpress.com/2006/02/397px-Charles_Darwin_by_G._Richmond.jpg

**Darwin cont. From collections & observations

Natural selection Mechanism for change in populations Organisms with favorable variations survive,

reproduce, & pass variations on to next generation

Published On the Origin of Species by Means of Natural Selection

http://uk.gizmodo.com/charles_darwin_l.jpg

Mechanisms of Evolution Populations evolve, NOT individuals Gene pool - all alleles in a population’s genes

together (remember: alleles: alternative forms of a gene)

Allelic frequency - % of any specific allele (p.405 snapdragons)

Genetic equilibrium - frequency of alleles remains same over generations = no evolution

How does evolution happen? - disrupting genetic equilibrium Mutations - caused by radiation or chemicals Genetic drift - alteration of allelic frequencies by

chance events (random, affects small populations greater)

Gene flow - Migration & Emigration Natural selection - allelic frequencies change

due to nature selecting for advantageous variations Stabilizing, directional, and disruptive

Stabilizing selection - favors average phenotypes

Spiders- larger spiders

eaten by predators

-Smaller spiders can’t

catch enough food

-Favors average size

Directional selection - favors one extreme (on graph, selects to left or right)

Woodpeckers-

longer beaks

eat more insects

buried deep in bark

(have more fitness)

Long beaks favored Can lead to

rapid evolution

Disruptive selection - eliminates intermediate phenotypes

In an environment,

medium-sized seeds

become less common

-Birds with smaller or

larger beaks have easier

time finding food

= higher fitness

How do changes in gene pool lead to evolution? Speciation - when members of similar populations no

longer interbreed to produce fertile offspring within natural environment

Geographic isolation - physical barrier divides a population Lava from volcanic eruptions, sea-level changes, rivers,

mountains Reproductive isolation - populations no longer mate and

produce fertile offspring Behavorial - different mating calls or seasons Different genetic material Polyploidy - having multiple chromosome sets

Speciation rates - 2 hypotheses, both supported by fossil record Gradualism - species originate through

gradual change of adaptations; slow & steady

Punctuated equilibrium - species originate quickly, in rapid bursts

Patterns of evolution Divergent evolution - occurs when populations

change as they adapt to different environmental conditions Adaptive radiation - ancestral species evolves into

many new species to fit various niches Hawaiiian honeycreepers; Darwin’s finches

Convergent evolution - unrelated species evolve similar traits because of similar environmental pressures Different cactus species around the world

*Adaptations: Evidence for Evolution Structural adaptations

Body parts of an organism that help it survive Ex. Teeth, claws, keen eyes, thorns,

Mimicry – more subtle One harmless species looks a dangerous one

Harmless fly looks like a wasp; scarlet kingsnake looks like coral snake

Two or more harmful species look alike Yellow jackets, honeybees, many wasps use same coloring to

say “Hey, stay away, I’ll hurt you!”

Camouflage – enables species to blend in

www.nature.com/.../n7023/images/433205a-f1

Photo Credit: Dan Hipes

http://www.outdooralabama.com/watchable%2Dwildlife/what/Reptiles/Snakes/scarlet.cfm

Photo Credit: AZ Herpetological Associationhttp://www.sloanmonster.com/images/coral.jpg

farm1.static.flickr.com/144/383488615_b937af4

lh3.google.ca/abramsv

Can you think of an example for camouflage?

I’ll show you some

*Physiological adaptations Can happen very quickly Changes in an organism’s metabolic

processes Antibiotic-resistance bacteria

Penicillin not as effective now Insects & weeds resistant to pesticides

Strains of drug-resistant TB

Articles on: -Antibiotic resistance -Crop pest evolutionMRSA podcast

*Indirect evidence for evolution Fossils

Assembling a puzzle without all the pieces What percentage of “Lucy” did they find?

Anatomy (p. 401 fig. 15.6) Homologous structures

Structural features with common evolutionary origin

*Indirect evidence for evolution

http://evolution.berkeley.edu/evosite/lines/IIhomologies.shtml

*Anatomy cont. Analogous structures

Body parts have similar function but not common ancestry Bird wing, butterfly wing

Vestigial structures Body part in present-day organism that no longer

serves its original purpose (but was useful at some time)

Our wisdom teeth, appendix, blind cave fish with eyes

http://evolution.berkeley.edu/evolibrary/article//evo_31

*Indirect Evidence for Evolution Embryology

Embryo – earliest stage of growth & development of plants & animals

Page 402 fig. 15.9: You had a tail and gills?? Biochemistry

Biochemical molecules: RNA, DNA, ATP, and many enzymes Compare amino acid sequences among organisms Enzyme - cytochrome c - involved in cellular respiration

P.403