Darwin & His Theories

The Origin of Species

In 1859, Darwin publish his ideas in a book, “The Origin of Species”

• Stated animals and plants changed gradually over time; still changing.

– Animals living today descended from animals living long ago. (Fossils)

Important Events in Darwin’s Life 1825-1827 – Darwin Studies Medicine at Edinburgh University, Scotland

1828-31 – Darwin studied to be a minister Cambridge University, England

1831-36 – Sailed around the world as a Naturalist on the Beagle

1859 – The Origin of Species was Published

1971 – The Descent of Man was Published

1881 – The Formation of Vegetable Mold through the action of Earthworms

Darwin’s Theory

3 Main Points: 1. Plants and animals have

more offspring than are needed to replace the parents.

2. The overall number of each kind of plant or animal mostly stays about the same.

3. The offspring of a set of parents are not all exactly alike.

Darwin’s Adventures on the Beagle From 1831-1836 – Darwin sailed around the world

Mendel and Darwin

Mendel was the father of modern genetics and wrote 2 papers in 1865 and 1869 but, they didn’t become popular until the 1990s.

• Although supportive, Darwin died in 1882 before Mendel’s work could be used to support Darwin’s theories.

The Puzzle of Life’s Diversity

• Biological Diversity- variety of living things.

• Evolutionary Theory- a collection of scientific facts, observations & hypotheses; it can explain the diversity of life on Earth.

• Evolution- change over time; the process by which modern organisms have descended from ancient organisms.

• Scientific Theory- a well supported testable explanation of natural events; supported by evidence & can be tested with new evidence.

• Theory- is a well supported TESTABLE explanation of phenomena that have occurred in the natural world.

Charles Darwin - Born in England

• He contributed more than any other scientist to our understanding of evolution.

• Voyage of the Beagle- sailed around the world stopping at the Galapagos Islands.

• He made numerous observations & collected evidence that led him to propose a theory about life changing.

• He noticed many plants & animals were well suited to their environment.

• He was impressed by how many ways organisms survived and produced offspring.

Darwin

• He collected fossils- preserved remains of

ancient organisms.

• Some fossils resembled organisms that

were still alive and others resembled

nothing he had ever seen before.

Galapagos Islands

• Islands west of South America that are close together but have very different climates.

• Darwin studied shell shape of the many different tortoises.

• He discovered many similar but different birds that turned out to be finches.

• Each species of finch had a different shaped beak which was a structural adaptation.

• Darwin observed that characteristics of many animals and plants varied among the islands.

Ideas that shaped Darwin’s Thinking

• Europeans believed the earth was young and living things had always been here, looking the way they do now. Rock and major geographic features were suddenly produced by a catastrophic event.

• He felt that many would find his ideas too shocking to accept but he began to put all of his work on paper.

• Several scientists influenced Darwin:

• Hutton- earth is shaped by geological forces

• Lyell- earth is shaped by geological forces

• Lamarck- in inherited acquired traits; organisms change over time.

• Malthus-predicted that human pop. Would grow faster than space and food would provide.

Darwin’s Case

• He was reluctant to publish his ideas because they were so radical.

• He was disturbed by his own findings which challenged fundamental scientific beliefs.

• When he heard a scientist name Wallace had the same idea as his, Darwin published his work.

On the Origin of Species

1859

Darwin Published his Book

• On the Origin of Species – 1859.

• The book provided evidence that

evolution has occurred.

• His theory on how evolution comes

about was based on artificial

selection.

• He believed that natural selection

occurs in nature.

Artificial & Natural Selection

Artificial Selection • Animal breeders select for breeding only animals with

the desired traits.

Ex. Crops, livestock & horses.

Natural Selection • Individuals differ & some of the differences can be

passed on to their offspring.

• More offspring are produced than can survive or reproduce.

• Individuals best suited to their environment survive & reproduce most successfully.

Ex. run fast, outsmart with behavioral tactics.

Artificial Selection Animal breeders select for breeding only animals with the desired traits. Ex. Crops, livestock & horses.

Banana Ancestor

Banana after many

years of the artificial

selection of traits by

humans.

Natural Selection- is the process by which

individuals that are better suited to their environment

survive and reproduce.

• Individuals differ & some of

the differences can be passed on to their offspring.

• More offspring are produced than can survive or reproduce.

Ex. run fast, outsmart with behavioral tactics. The giraffes are also an example: Long neck giraffes survived because of their abilities to reach their food source.

Finches

• The warbler finch (top)

boasts a thin, sharp beak

best suited for spearing

insects.

• Ground finches' shorter,

more robust beaks

(center) are adapted for

eating seeds found on the

ground.

• Those of cactus finches

(bottom) are shaped for

getting seeds from cacti.

Does something like artificial

selection work in nature?

Yes - Darwin called it Natural Selection!

Charles Darwin Overview

• Darwin noticed that animals had different variations which enabled them to survive in their environment.

• Natural selection (survival of the fittest)- he believed that the organisms best equipped to survive in an environment would reproduce and become the dominant species.

Survival of the Fittest • Animals prey on other animals. Some die and

some survive.

• Fitness- the ability to survive & reproduce in a

specific environment.

• Only the fittest organisms pass on their traits,

thus the species change over time.

• Adaptation- an inherited characteristic that can

be physical or behavioral.

• Speciation- is the formation of a new species.

• Speciation can occur because adaptations which were obtained, varied to a degree where the species with different variations do not mate anymore.

Organisms not equipped to survive

may become extinct.

• Living in an unstable environment may

contribute to variations among organisms as

they compete to survive.

• Living in a stable environment slows an

organism’s need to evolve or to go through

speciation.

• Biodiversity- is the sum of the variety of

organisms in the biosphere.

Say a population of rabbits lives in

Pennsylvania. Most rabbits are a shade

of brown, but every so often due to

natural variation a white rabbit is born.

These white rabbits tend to stand out in

the dark forest and are eaten at a

higher rate by predators. Thus they

rarely survive to reproduce and pass on

their white fur coat to a new generation

of rabbits. In the forest, brown coated

rabbits are the most fit to survive.

As the rabbit population grows they start to inhabit Canada and the far north.

Here snow covers the ground 75% of the year. The white furred rabbits are still occasionally born, but here they

tend to survive better than their brown coated relatives. Here the white fur is

an adaptation and the white rabbits survive longer and produce offspring. Eventually all the rabbits of the north

are white and brown furred rabbits are rarely seen. White rabbits are the most

fit to survive there.

Peppered Moths

Peppered Moths

A trait, that exists only by chance

through the natural variation of life is

naturally selected as more fit and

therefore to survive and reproduce

more offspring than others of the

population. This is known as

Darwin’s Theory of Natural Selection

or Survival of the Fittest.

Lamarck Theory of Evolution

• Lamarck’s theory- he believed that organisms had the ability to obtain or even lose adaptations depending on their use or non-use of the organ. (Vestigial organ is an useless organ.)

• He believed that the crab’s claw would increase in size because of extensive use and that the new adaptation would pass on

to their offspring.

Darwin –vs- Lamarck (Long neck vs Short neck Giraffes)

• Darwin believe that 2 types of giraffes existed, but the short neck giraffes died off because they could not reach their food source. Only the long neck giraffes were able to survive and reproduce successfully.

• Lamarck believe that the giraffes continued to attempt to reach for the tree leaves and in time their necks increased in length creating the giraffes that we see today.

Principle of Common Descent

• All species come from common ancestors.

• It links all organisms on Earth into a single

tree of life.

Ex. Tigers-panthers-cheetahs,

felines-horses-dogs-bats, mammals-birds-

alligators-fish.

Evidence for Evolution 1. Evidence from the fossil record- comparing fossils from older & younger rock

layers documents the fact that evolution has occurred; it is a detailed

record of evolution.

2. The geographical distribution of species-the presence of similar

environments suggests natural selection. Ex.-the finches could have

descended from common ancestors on the mainland.

3. Homologous structures- they have different mature forms but develop from

the same embryonic tissues. Bone structure is the same but they look

different. All are adapted to survive in different environments. Ex. Legs,

wings, fins.

Vestigial organs- some homologous structures no longer serve important

functions in descendants. Their size is reduces.

4. Similarities in embryology- early stages, or embryos, of many animals are

very similar.

5. DNA evidence

Fossil Record

Common ancestor- some scientist believe that

many organisms may have a common ancestor

because of how the embryos resemble each other

• What am I?

Common ancestor- some scientist believe that many

organisms may have a common ancestor because of how

the embryos resemble each other

• Puppy dolphin elephant

DNA Evidence

Homologous Structures

Structures that have very

different functions, but

share a common

evolutionary origin.

Homologous Structures

Homologous Structures Example: the wing of a bat, the flipper of a dolphin

and the hand of a human all have five ‘fingers.’

These structures despite having completely

different functions are similar because they all

come from the common ancestor of all

mammals.

Homologous structures are structures that have

different mature forms in different organisms but developed from

the same embryonic tissue. COMPARE THE BONES OF THESE

DIFFERENT ORGANISM. Scientist believe that they are similar because of

similar embryonic tissue.

Analogous Structures

Structures that have similar

functions, but no common

evolutionary origin.

Analogous Structures Example: the wing of a

bat and the wing of an

insect both serve the

same function (to allow

the organism to fly) but

they come from very

different evolutionary

origins. Bat wings are

made of bones and

skin, insect wings have

neither.

Vestigial Structures Example: Your appendix. Once upon a time it

was used to store the inedible things people

once ate like bark, fruit peelings and even rocks.

This is why a surgeon can remove it without

causing any harm.

Vestigial Structures

Another Example:

A whale has

thigh bones left

over from its

ancestors that

were cow-like

land animals!

Analyzing Geological and

Environmental Changes

• On standardized exam you

may be asked to analyze

changes over time.

• Analyze the fossil layers to

the right and explain what

happen to the area.

• NOTE: Play close attention to

the arrow to the right. (Shows

the direction of the time line)

Analyze the evolution of the horse. List various

changes that took place in each column.

Analyze the diagram below of a species A thru G.

What does the diagram tell you about the 7

species? Genetically, which species are probably

the most similar?

Human Evolution

Primates- is a mammal such as an ape,

monkey lemur or human.

• Most primates have an opposable thumb. (a thumb

that can be brought around opposite of the fore-fingers)

• Some primates have a prehensile tail. ( a muscular tail

that can grasps or wrap around branches.)

• Humans are bipedal. (Can walk on two legs)

• Hominids- are human like, bipedal primates.

• Stereoscopic vision- eyes are centered in the

front of the head giving primates the ability to

perceive distance. (Need to throw things like a

ball)

Evolution

Chapter 11

Evolution of Populations

Genes & Variations

What we already know:

• Traits are controlled by genes.

• Many genes have at least 2 forms or

alleles.

• Individuals of all species are heterozygous

for many genes.

Genetic Variation

• Studied in populations

• Population- a group of individuals of the same species that interbreed; share a common group of genes.

• Gene Pool- results from interbreeding in populations; it’s all the genes that are present in a population; contains 2 or more alleles for each inheritable trait.

• Relative Frequency- the # of times the allele occurs in a gene pool, compared with the # of times other alleles for the same

gene occur; it’s often a %. Ex. An allele makes up ¼ of population’s allele for a given trait. The relative frequency is 25%.

• In genetic terms, evolution is any change in the relative frequency of alleles in a population.

2 Main Sources of Genetic

Variation • Mutations

• Gene Shuffling • Occurs during gamete production; results in many

different combinations.

• Single gene trait controlled by 1 gene.

• 2-3 different genotypes are possible.

• Compare populations gene pool to a deck of cards. Shuffle & you get a different hand each time but it never changes the # of kings, aces, etc.

Polygenic Trait

• Can have many possible genotypes,

producing many possible phenotypes.

• Controlled by 2 or more genes, each may

have more than one allele. Ex. Height.

• Bell Shaped Curve

• How phenotypes are expressed. • Most people are in the middle of the curve

16-2 Evolution as Genetic

Change • Natural Selection acts directly on

phenotype. Ex. Lizard color.

• Natural selection on Polygenic Traits are

more complicated. • Directional

• Stabilizing

• Disruptive

Directional Selection

• When individuals at one end of the bell-shaped

curve have higher fitness than individuals near

the middle or the other end of the curve.

• The curve shifts toward the higher fitness end.

• Ex.- birds with larger beaks will have higher

fitness if a small-medium seed shortage occurs.

Directional Selection

Stabilizing Selection

• When individuals near the middle of the curve

have higher fitness than those on either end of

the curve.

• This is where the average form of trait is.

• The curve narrows around the middle

• Ex.- a babies birth weight. Less wt., lower

survival rate. Higher wt., difficult birth.

Stabilizing Selection

Disruptive Selection

• When individuals at the upper and lower ends of

the curve have higher fitness than the

individuals near the middle.

• The curve develops a peak at each end and a

low point in the middle.

• Ex.- Medium bird seed has a shortage. Small &

large bird seed are abundant. Birds with small &

large beaks will have greater fitness.

Disruptive Selection

Genetic Drift

• Allele frequencies change.

• Occurs in small populations.

• Individuals with a particular allele leave more descendants than other individuals.

• Alleles become more or less common by chance.

• The only similarity to natural selection is that they involve a change in a population’s allele frequencies.

Genetic Equilibrium

Hardy-Weinberg Principle • A situation in which allele frequencies of a

population remain constant. • 5 conditions required to maintain genetic equilibrium:

– Random mating.

– Population must be very large.

– There can be no movement into or out of the population

(migration).

– No mutations.

– No natural selection

When all 5 are met, evolution will not occur.

Process of Speciation

• Speciation- formation of new species

– For 1 species to evolve into 2 new species:

• Gene pools of 2 populations must become

separated.

• They must be reproductively isolated.

• Ex. – finches on the Galapagos islands.

Reproductive Isolation

• When members of 2 populations cannot

interbreed & produce fertile offspring.

– Behavioral- different courtship rituals.

Ex. Songs.

– Geographical- populations are separated by

geographic barriers. Ex. Mountains, rivers.

– Temporal- populations reproduce at different

times. Ex. Pollination.

Speciation of Darwin’s Finches

1. The species evolved on the Islands from a single species of founding birds.

2. They traveled from mainland South America to one island to found a new population.

3. They survived & reproduced then crossed to a 2nd island.

4. The became geographically isolated & gene pool was no longer shared.

5. Seed size on the island favored large beak birds.

6. Large beak birds reproductively isolated & evolved into a new species.