“Extinction is the rule. Survival is the exception.” –Carl Sagan

“Nothing in biology makes sense except in the light of evolution.” -Dobzhansky

“The human’s place in the universe will be set in the scheme of evolution, the product of our biological

inheritance.” –Walter Gilbert

Evolution

Evolution

Evolution is genetic change in a population over time.

It is a scientific theory based on an abundance of FACTS and EVIDENCE.

Charles Darwin was the first scientist to propose the theory of evolution, in 1859.

Darwin’s Observations

He studied finches (birds), tortoises, plants, and animals on the Galapagos islands.

Darwin’s Conclusions

The Earth is very old and constantly changingLiving things change over time.Living things are related to plants and

animals that used to exist but are now extinct.

A very brief history of time

The Earth is 4.6 billion years oldLife appeared (bacteria in the ocean) 3.8 billion

years ago – everything alive on the planet today is descended from this, our “last universal common ancestor” or Luca

500 mya: microscopic aquatic plants and animals300 mya: reptiles, amphibians and insects evolve65 mya: small rodent like mammals evolve20 mya: the first modern primates (apes, monkey,

lemurs) evolve100,000 years ago: the first modern humans appear

Origins of Life

How did life start?The atmosphere has nitrogen, methane, and

ammonia. The oceans had water, lipids, amino acids, and other carbon compounds.

Energy from the sun, volcanoes, and lightening helped amino acids become protein and DNA, which is the basis for life on Earth and formed simple cells.

Other theories? Meteorites

Natural Selection

Individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted.

This is called natural selection, and is also referred to as survival of the fittest.

A tale of two giraffes...

Lamarck: The giraffe stretched its neck, which got longer, and its babies had long necks.

Wrong! If your arm was cut off, would you have a baby with one arm?

Darwin: Some giraffes were born with long necks, some with short, the short necks died and the long necks ate food and made long necked babies.

Right! If you are lucky enough to have a good trait, you will reproduce and pass it on.

Artificial Selection

If humans choose organisms with specific characteristics and breed them, this is called artificial selection.

For example: dog breeding

Ancestral dog

Hundreds tothousands of years

of breeding(artificial selection)

Evidence for Evolution

1. Fossils: preserved remains of dead organisms that show how life has changed over time.

Carbon dating measures radioactivity and gives us exact dates of rocks and fossils, which is how we know how old things are.

Evidence for Evolution

2. Biogeography is the geographic distribution of species (where animals live).

Plants and animals in different parts of the world are related because they share common ancestors.

All the continents used to be together in a super continent called Pangaea.

Evidence for Evolution

3. Comparative Anatomy: living species have similar bones, which shows they shared a common ancestor.

Humans, cats, whales, and bats all have the same number and type of bones in their arms and legs.

Human Cat Whale Bat

Evidence for Evolution

4. Comparative Embryology: closely related organisms look similar when they are embryos

This shows that they share a common ancestor, and are all related.

Fish, frogs, snakes, birds, apes, and people all have gills and tails as embryos.

Evidence for Evolution

5. Molecular Biology: Scientists compare DNA and amino acid sequences between species to see how closely related we are.

Humans and chimps share 99% of their DNA, which shows they are related and come from a common ancestor.

5 ways evolution happens

1. Genetic Drift is a change in the gene pool due to chance (survival of the fittest)

Ancestral canine

Thousands tomillions of years

of natural selection

How evolution happens

When an event (like a fire, flood or earthquake) drastically reduces the population size only a few organisms survive.

These are the ones that have the best adaptations and are the most fit.

2. This is called the bottleneck effect.

Originalpopulation

Bottleneckingevent

Survivingpopulation

How evolution happens

3. The founder effect is when some individuals leave a population and start living somewhere new.

The new population starts with less genes, and there will be a lack of genetic diversity.

How evolution happens

4. When individuals either enter or leave a population, so do their genes. This is called gene flow and it affects the processes of natural selection and evolution.

5. Mutations are random changes in DNA and can create new proteins and new characteristics. If they are beneficial, they are passed on to offspring.

Mass Extinctions

5 major mass extinctions also contributed to Earth’s evolution.

The Permian Extinction occurred 245 mya and was caused by global warming. 95% of all plants and animals went extinct.

65 mya, a large asteroid hit the Earth and caused the Cretaceous Extinction which led to the death of dinosaurs.

Every mass extinction reduced the diversity of life, but those animals with the best adaptations survived and reproduced (like mammals)

Speciation

A species is a population of interbreeding organisms that can produce viable, fertile offspring.

How new species form

Stabilizing selection: average individuals are favored. Ex: average sized spiders

Directional selection: one trait is more likely to reproduce than another. Ex: long beaked woodpeckers

Disruptive selection: extreme traits are more likely to survive and reproduce. Ex: black moths

How new species form

Geographic isolation: physical barriers divide a population (Ex. Grand Canyon)

Reproductive isolation: can no longer mate and produce fertile offspring (ex. CA salamanders)

Gradualism vs. Punctuated

How fast does evolution go?Gradualism says that it happens slowly and

steadily over timePunctuated equilibrium says that it happens

quickly in rapid burstsThere are examples of both! Gradualism: dinosaurs into modern birdsPunctuated: finches in the Galapagos and

extreme weather (Grant study)

Speciation

2 animals cannot produce viable, fertile offspring if they are from different species.

This is because of either pre-zygotic barriers which prevent the animals from ever meeting and reproducing, or post-zygotic barriers that prevent a zygote from developing into a fertile adult.

Pre-Zygotic Barriers

1. Habitat isolation: 2 species live in different habitats and don’t see each other

2. Temporal isolation: 2 species breed at different times of the day or year

3. Behavioral isolation: courtship rituals are species specific, and don’t attract other species

4. Mechanical isolation: the sexual pieces don’t fit together

5. Gametic isolation: even if sex occurs, the egg and sperm can’t meet

Post-zygotic barriers

1. Reduced hybrid viability: hybrid babies die before reaching reproductive age

2. Reduced hybrid fertility: hybrid babies are sterile and can’t reproduce

3. Hybrid breakdown: first generation babies can breed, but their children are infertile (F2)

Speciation

There are a few exceptions, called hybrids: Lion + tiger = liger (the grandchildren can’t

reproduce) Horse + donkey = mule (all sterile) Polar bear + grizzly bear = pizzly (too soon to tell if

they are fertile or not)

Hardy-Weinberg

The Hardy-Weinberg equation shows that in a changing environment, evolution always happens.

If all 5 of these conditions are met, evolution will not happen in nature:

1. Large population2. Random Mating3. No gene flow 4. No mutations 5. All individual are equally “fit”

Hardy-Weinberg

The Hardy-Weinberg equation is p2 + 2pq + q2 =1

The variables stand for:p = frequency of the dominant allele (A)q = frequency of the recessive allele (a)2pq = chances of being heterozygous (Aa)p2 = chances of being AAq2 = chances of being aa

The results of evolution

First, there were only bacteria cells.These evolved into eukaryotic multi celled simple

animals.The first animals lived in the ocean and evolved into

fish.Lungfish were able to survive on land and evolved into

amphibians and reptiles.Reptiles evolved into birds and small mammals.Small rodent like mammals evolved into lemurs, which

then evolved into apes, monkeys, and humans.Apes and monkeys are our close cousins, and we share

a common ancestor.