Evolution

A history of Evolutionary Thought

Humans did NOT come from apes

Early Philosophies

• Plato: organisms existed in an ideal form– Unchanging

• Aristotle: categorized living things– Ordered scheme called Ladder of Nature

• Primitive animals at the bottom• Humans at the top

Evidence – Before Darwin

• Exploration of new land– New creatures existed

• Similarities existed• Differences apparent

• Fossil organization– Bottom rock layers contain more primitive

fossils– Top rock layers contain fossils that lived later

Mechanisms of Evolution – Before Darwin

• Jean-Baptiste Lamarck’s Theory of Inheritance of Acquired Characteristics– Organisms could change themselves in life– Organisms gain traits they need– Pass on these changes to offspring

Lamarck

• Theory ultimately discarded

• There is no conscious or thought in evolution

• Think about it... – If you lose an arm, will all your kids have one

less arm?– If you are born with a birthmark, will all your

kids have it to?

Darwin’s Journey

• Traveled on the HMS Beagle

• Traveled many places

• Made many observations of new species not yet documented

Darwin’s Observations

• Snakes with rudimentary hind limbs

• Snakes with no rattle that shook their tails like rattlesnakes

• Penguins using wings to paddle, not fly

Darwin’s Observations

• Many species on the Galapagos Islands unlike species on the mainland

• Vast amount of finches on the island that were similar, but had different eating habits and therefore different beak structure

Darwin’s Ideas

• Proposed that evolution occurs by natural selection

• Studied ideas about 4 0 years

Competition?

• Wallace in America– Came up with the

same ideas– Wrote to Darwin– Darwin rushed his to

publication first

Natural Selection

• Both naturalists came up with the idea independently of the other– Both published their findings in 1858

• Logically some organisms would be able to survive better than others– They would pass on their traits to their

offspring

So What is Evolution?

• Evolution means change

• More than change over time– Trees lose their leaves– Mountains rise and erode

• Evolution involves descent with genetic inheritance

• Descent with modification!

Questions to ask

• How can one explain all these makeshift arrangements?

• How are there so many similarities and at the same time so many differences?

• What causes these differences?

What Darwin was saying

• Evolution occurs by natural selection

• Evolutionary Theory was proposed

• Today there are many evolutionary theories

What will we talk about?

• Briefly discuss the Theory of Evolution– Science trying to explain how life began using

natural methodology

• Investigate evolution– Science explaining why and how organisms

change through time– Organisms pass on these changes– Has been observed in labs and in nature

Evolutionary TheoryHow did life begin?

• Early life began 3.5 – 4 billion years ago

• Early organic compounds present– Made of carbon

• Conditions were very different then

• Spontaneous generation possible then– not known to be possible today

Time• Geologists estimate Earth to be about 4

billion years old

• Life was not on Earth in its beginnings

Beginnings of Life:First PROKARYOTES:

1. Accumulation of small organic molecules• Monomers such as amino acids &

nucleotides

2. Joining of monomers to make polymers• Proteins & nucleic acids

3. Joining of polymers into droplets

4. Able to pass on these characteristics• Heritability

Miller & Urey Experiment

• Attempted to simulate conditions on early Earth

• Mixed water vapor, hydrogen, methane, ammonia with energy

• Amino acids & other organic compounds formed

See the experiment See the experiment

Hmm???

• The first organisms on Earth were probably

a. Autotrophic, aerobic eukaryotes

b. Heterotrophic, aerobic eukaryotes

c. Autotrophic, anaerobic prokaryotes

d. Heterotrophic, anaerobic prokaryotes

First Organisms

• Very primitive

• Prokaryotic– Single celled– Circular DNA

First Eukaryotes

• Theory of Endosymbiosis– One prokaryote absorbed (endo) another

prokaryote (mitochondria)– Instead of digesting it, they began to work

together (symbiosis)– Different DNA in mitochondria, chloroplast,

and nucleus

See it happen

How might Evolution happen?

• Mutations in DNA– Changes code– Can change characteristics– Random– Many times lethal– Can be helpful

Mutations

• Passed on to offspring = evolution

• Not passed on = just a mutation

Example: Antibiotic Resistance

• Antibiotics kill bacteria• Mutation happens in bacteria

– Antibiotic does not kill that 1 bacteria– That one bacteria divides into 2 (passes on

mutation)– Those 2 into 4, etc.

• Now there is a population of bacteria that are resistant to that antibiotic

• Great for the bacteria; bad for humans

Darwin’s Natural Selection

• Organisms produce more offspring than can survive

• Populations tend to remain constant over time

• Organisms in a species will show differences due to different genes

Darwin’s Natural Selection

• Some variations passed on to offspring

• Not all organisms survive– Predators– Disease– Competition

• Organisms that are the most fit for the environment will survive and make more like themselves

Evolution

• Organism

Population

Community

Ecosystem

• Smallest unit in which evolution occurs is population

Adaptations

• Adaptation– A certain trait arises from a mutation that

makes that organism more fit for its environment

• Examples– Camel

• Broad feet, little sweat/urine, sandy color

– Polar bear• Blubber, white hair, big feet

How Organisms Change

• Species– Like organisms capable of interbreeding

naturally

• Evolution– Genetic change in a population over a long

period of time

• Gene pool– Sum of all genes in a population

How Organisms Change

• Genetic Drift– Small populations more effected by random

chance

• Adaptive Radiation– Slow change of genotype and phenotype of a

species from common ancestor– Become more diversified over time

Points on Evolution

• Natural Selection– Does NOT cause genetic changes in

individuals– Befall individuals, but occurs in populations

• Evolution– Change in genotype frequency– Not necessarily “good” or “progressive”

Mechanisms of Evolution

1. Mutation

2. Migration

3. Small population

4. Nonrandom mating

5. Natural selection

Natural Selection

• When nature ‘selects’ for ‘better’ traits

• NOT done consciously

• If it works better, it will most likely:– Survive longer– Reproduce more– Spread its genetics more

• Bacterial resistance

• Peppered moths

Types of Natural Selection

• Directional selection

• Stabilizing selection

• Disruptive Selection

Directional Selection

• Individual have extreme values of a trait

• Populations move in a certain direction

• Example

• Climate get colder, moves to favor those with thicker fur

Stabilizing Selection

• Favors average

• Against those who are extreme

• Example– Large lizards more subject to predation– Small lizards difficult in defending territory– Average size best of both worlds

Disruptive Selection

• Adapts individuals in a population to different habitats

• Favors either extreme– Llike directional selection, but favors more than one

• Areas that provide different resources• Example

– Galapagos finches had different food choice– Small bird feeds on smaller seeds– Large bird feeds on larger seeds– Average size bird competes with both

Terms

• Adaptation– Trait/s that help an organism survive and

reproduce

• Coevolution– Evolve together– Usually between predator and prey– Fastest wolf catches the deer; fastest deer

gets away

Terms

• Speciation– The rise of a new species

• Gene pool– The genes in a population

Mutations in Common Animals

• Rabbit story: Big ears vs. small ears– Short-eared rabbits

• Roaches: How did they survive– Big, fat, cockroach

• Antibiotic resistant bacteria– We are helping by not using antibiotics

correctly

Evidence of Evolution

• Fossil record• Comparative Anatomy• Homologous Structures• Vestigial Structures• Embryonic Development• Biochemical & Genetic Analysis• Artificial Selection• Observed Natural Selection

Fossil Record

• Progressive – from ancient to modern form• Not complete

– Some better represented than others

• Fossil forms– Bones, teeth, shells– Petrification of softer parts

• Replaced by minerals

– Whole animals• Glaciers, amber

Fossil Record

• What creatures looked like

• How long ago they lived

• The deeper the fossil, the older it is

• Shows how species have changed over millions of years

• Incomplete– Very few plants & animals become fossils

Comparative Anatomy

• Organisms that evolve in similar environments develop similar structures

• Natural selection drives species to develop structures best suited for their environment

Comparative Anatomy

• Convergent evolution– 2 similar species have similar forms

• Whale & shark

• Analogous structures– Outwardly similar function

• Wing of fly and wing of bird

Homologous Structures

• Similar in structure regardless of use– Forearm of vertebrates

• Human, cat, whale, bat

• Derived form same common ancestor

Vestigial Structures

• Structures with no apparent purpose– Pelvic bones of whales– Human tail bone– Human appendix– Emu wing

Embryonic Development

• All vertebrates look similar in early development

• All have gill slits and a tail (even humans)– Gill slits are skin folds in early developing

organisms

Biochemical & Genetic Analysis

• Similarities between organisms’ DNA and protein structures

• DNA sequencing allows us to tell which organisms are more closely related

Artificial Selection

• Selective breeding• Produce wanted traits in offspring

– Plump chickens– Dairy cow that produce more milk

• Select the best offspring and breed them together

• Reduces the number of gene in a population’s gene pool

• Lessens diversity

Causes of Extinction

• Drastic changes in environments– Food source is removed

• Populations have trouble adapting

• Interactions with other organisms– Competition for resources

• Habitat change– Leading cause of extinction!– Catastrophic events

• Human activities

Hmm???

• Why is genetic homozygosity dangerous to a nearly extinct species (small population)?