Theory of Evolution

Chapter 16 & 19.2

16.1 Darwin’s Voyage• Early 1800s – Geologists were discovering the

world was very old, and suggested that the world is constantly changing.

• Evolution – the process of change over time.• Charles Darwin sailed on a 5 year around the

world journey on the Beagle.– He collected plant and animal specimens all along

the way.– Devolped a theory that

• explains how modern organisms evolve millions of years.• Tells how modern organisms came from common

ancestors.

The Beagle• Darwin took notes and observations along with specimens on his

trip.• He was amazed of the number of new organisms he found

– Ex. He collected 68 different types of beetles in one day• He noticed patterns

– Species vary around the world– Species vary locally– Species vary over time

Species Vary Around the World• Visited habitats in: South America, Australia,

and Africa.• Grasslands of South America had large

flightless bird called rhea• Grasslands of Africa has ostriches• Grasslands of Australia had emus.• He was confused that there were no rabbits

in Australia and no kangaroos in England since their habitats could support those animals.

• Places around the world that had similar habitats often had different animals that were ecologically similar.

Species Varying Locally• Darwin noticed that different, yet

related, animal species often occupied different habitats within a local area.

• The shape of the tortoises’ shells corresponds to different habitats. – Isabela Island has high peaks, is rainy, and

has abundant vegetation that is close to the ground. • Isabela Island tortoise has a dome-shaped

shell and short neck.

– Hood Island, in contrast, is flat, dry, and has sparse vegetation.• A long neck and a shell that is curved and

open around the neck and legs allow the Hood Island tortoise to reach sparse, high vegetation.

Species Varying Locally

• Darwin also notices several kinds of small brown birds.

• Their beaks looked so different he thought they were unrelated however these birds are actually very closely related.

Species Varying Over Time• Darwin collected fossils

(preserved remains of ancient organisms).

• Some fossils did not look like living organisms while others did.

• The extinct glyptodont lived where the armadillo lives today and looks like a giant armadillo.

• This raised questions: Why do they look alike? Why did the glyptodont disappear?

Solving the Puzzle

• On the voyage home Darwin started thinking about the patterns he saw and sent his specimens to experts.– Darwin began to wonder whether different

Galápagos species might have evolved from South American ancestors.

– He spent years actively researching and filling notebooks with ideas about species and evolution.

– The evidence suggested that species are not fixed and that they could change by some natural process.

16.2 Shaping Darwin’s Thinking• Hutton and Geological Change

– Suggested great forces under the surface push mountains upward.– The mountains are worn down by rain and wind.– These process are very very slow.– Deep Time- Earth’s history is so long that it is difficult to imagine.

• Lyell’s Principal of Geology (uniformitarianism)– Stated Laws of nature do not change.– Geological process of the past work the same way as today.– Volcanoes release lava the same, rivers cut canyons the same.– These processes form the mordern landscape over millions of

years.• Hutton and Lyell concluded that the Earth is very old and the

processes that changed Earth is the past are the same processes that operate today.

Lamarck’s Hypothesis of Evolution

• Throughout 18th century a growing fossil record supported that life somehow evolved.

• French naturalist Lamarck proposed: Organisms can change during their lifetimes by selectively using or not using carious body parts. Individuals could pass these acquired traits from parent to offspring enabling species to change over time.

Lamarck cont.• Lamarck figured all organisms have an inborn urge to

become more complex and perfect. Therefore all organisms change and acquire features that help them.

• Acquired characteristics – traits altered by an organism during its life.– Ex. Water birds developing longer legs for wading deeper into

the water.• Inheritance of acquired traits – Passing of acquired traits

from parent to offspring.– Ex. Water birds after a few generations have longer and longer

legs.

Evaluating Lamarck• What’s incorrect– Organisms do NOT have the inborn drive to become

more perfect.– Evolution does not occur in a predetermined

direction.– Traits acquired by individuals during a lifetime cannot

be passed from parent to offspring.• What’s correct– First person to suggest that species are not fixed and

change over time.– First person to try to explain evolution scientifically

using natural processes.

Population Growth

• 1798 English economist Thomas Malthus noticed that humans were reproducing faster than people were dying out.– If this stayed unchanged, there would not be

enough food and living space for everyone.• Darwin realized this occurred to every other

organism as well.– Stated most offspring die before reaching maturity

and only a few of those manage to reproduce.

Artificial Selection

• Artificial Selection - Humans choosing certain characteristics to get passed down to offspring.– Breeding Dogs– Farmers growing livestock– Farmers grow crops– Pigeons

• Natural Variation provided the raw material for evolution. This was Darwin’s scientific explanation for evolution.

16.3 Darwin Presents His Case

• Evolution by Natural Selection– Darwin wrote The origin of Species which combined

his own ideas with those of Malthus and Lamarck.– The Struggle for existence – members of a

population compete to obtain food, living space and other limited necessities of life.

– Adaptation – any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment.• Ex. Tiger Claws, camouflage, avoidance behaviors

Adaptations

Evolution by Natural Selection• Variation– Variation within a species allows some animals an

advantage in a population. • Predators that are faster with longer claws/sharper teeth

can catch more prey.• Prey with better camouflage can be avoided better.

• Survival of the Fittest– Fitness – how well an organism can survive and

reproduce in its environment.• High fitness are individuals with adaptations that are

well suited to their environment allowing for survival and reproduction.

• Survival – staying alive and reproducing and passing down genes to the next generation.

Natural Selectiona mechanism for evolution

• Natural Selection – process by which organisms with variations most suited to their local environment survive and leave more offspring.

• Natural selection occurs under 3 conditions:– in any situation where more individuals are born

than can survive (struggle for existence)– there is natural heritable variation (adaptation &

variation)– Variable fitness among individuals (survival of the

fittest)

Natural Selection

Natural Selection

• If the environment changes an adaptation that was better fitted may no longer be the best fit.

• No clear path is taken for selection.

Common Descent

• Over time, adaptation could cause successful species to evolve into new species.

• Descent with modification – living things are descended with modifications, from common ancestors.

• Deep time supports the theory of descent with modification.

• Principal of common descent – all species, living and extinct, are descended from ancient common ancestors.

16.4 Evidence of Evolution• Biogeography – the study of where organisms live now and

where they and their ancestors lived in the past.• Patterns in distribution of living and fossil species tell us

how modern organisms evolved from their ancestors.• Two significant biogeographically patterns– Closely Related but Different – Galapagos species evolved from

mainland species. Over time, natural selection produced variations among populations that resulted in different but closely related island species.

– Distantly Related but Similar – Similar habitats around the world produced distantly related organisms. Emus, Ostriches, & Rheas have different body structures show they are distantly related but underwent similar selection pressures to develop similar adaptations.

Age of Earth and Fossils• The Age of the Earth

– Evolution takes a long time, so the Earth is old.– Radioactivity determines the age of rocks, fossils and the

earth. – Earth approx. 4.5 billion years old.

• Recent Fossil Finds– Many recent discovered fossils form series that trace the

evolution of modern species from extinct ancestors.– One recent discovery is the evolution of whales from land

mammals.– Another is between birds and dinosaurs and fish and four-

legged land animals.– The history of life is not complete but the evidence we do

have tells an unmistakable story of evolutionary change.

Recent Fossil Finds

Comparative Anatomy• Homologous Structure – structure that

are shared by related species and have been inherited from a common ancestor.– Evolutionary theory explains the existence

of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.

– Similarities and difference between homologous structures help determine how recently species shared a common ancestor.

– Ex. Forelimbs of birds and reptiles are more similar than that of mammals so birds are more closely related to alligators than bats!

Comparative Anatomy• Analogous Structures– Homologous structures are common but does not mean functions

are common.• Ex. Bird wing and leg of a horse.

– Analogous structures – structures that share common function but not common structure.• Ex. Wing of a bird and wing of a bee.

• Vestigial Structures– Vestigial structures – inherited from ancestors but have lost much

or all of their original function due to different selection pressure acting on descendants.• Ex. Hipbones in dolphins. On land hips are useful, but in the water the

function was lost.

– Doesn’t disappear because structure doesn’t affect fitness, so elimination is unnecessary.

Embryology

• Early developmental stages of vertebrates look very similar.– The same groups of embryonic cells develop in the

same order in a similar patterns to produce many homologous tissues and organs

– Gives further evidence that organisms descended from a common ancestor.

Genetics and Molecular Biology• Genetic code is almost identical in all organisms (yeast,

bacteria, plants, fungi & animals).– Powerful evidence of evolution from common ancestors

• Some of the strongest supporting evolutionary theory comes from genetics.– Mendel, Watson & Cricks

• Mutations and reshuffling of genes during sexual reproduction produce heritable variation on which natural selection operates.

• Homologous proteins share extensive structural and chemical similarities.– Cytochrome c (cellular respiration) in all cells

Darwin and his Finches• Darwin proposed that natural selection shaped the beaks of

different finches as they adapted to eat different foods.• 2 testable hypotheses for this:

– For beak size and shape to evolve, there must be enough heritable variation in those traits.

– Differences in beak shape and size must produce differences in fitness.

• Tested by Princeton University.– Found during dry periods birds with larger beaks survive better– Changes in food supply created selection pressure that caused finch

populations to evolve within decades.– Proved that competition and environment drive natural selection.– Princeton’s study shows that variation within a species increases

the likelihood of the species’ adapting to and surviving environmental change.

19.2 Patterns & Processes of Evolution

• Macroevolution patterns –changes in anatomy, phylogeny, ecology, and behavior that take place in clades larger than single species.