Darwin & Theory of Evolution by Natural Selection

Chapter 22

Evolution- Just a Theory?

• Theory vs. Law vs. Dogma

• Theory – explain

• Laws describe

• Dogma is not tested – beliefs

• Science is limited to things we can measure, test.

• Hypothesis – is an “educated” guess to explain a problem,

Scientific Method

• Problem, observation

• Background information, literature search

• Hypothesis based on previous work

• Experiment to test hypothesis

• Analyze results

• If hypothesis supported – publish a paper.

Darwin’s Theory• Populations have inherent variation among

individuals.

• These traits are heritable

• Resources in the environment are limited

• Populations have a greater fertility than their environment can sustain.

• Populations would grow exponentially, but most remain stable in size.

A population of Liguus fascitus

Variation in shell coloration patterns

Fig. 22-10

Darwin’s Theory continued:

• There is a struggle to survive among the offspring called Natural Selection.

• The survivors are better fit

• Fitness is the ability to have more offspring (frequency of genes in the genepool).

Natural Selection

• “struggle “ or competition does not have to be a fight to death

• may just be as simple as a seed germinating earlier and getting established first. It produces 120 seeds. A later germinating plant makes only 50 seeds.

• “Fitness” is the success rate of the offspring in future generations.

Fig. 22-7

Fig. 22-19

Hawks andother birds

Ostriches

Crocodiles

Lizardsand snakes

Amphibians

Mammals

Lungfishes

Tetrapod limbs

Amnion

Feathers

Homologouscharacteristic

Branch point(common ancestor)

Te

trapo

ds

Am

nio

tes

Bird

s

6

5

4

3

2

1

Some Evidence for Evolution

• Microevolution- antibiotic, pesticide resistance– Artificial selection

• Fossil record• Biochemical comparisons

– Protein sequences– DNA, gene comparisons

• Morphological comparisons• Embryology• Biogeography• Genetically modified organisms

Fig. CO 13

All made by Artificial Selection from wild mustard

Artificial Selection: human designed breeding of plants and animals for desired traits by selecting which individuals get to reproduce.

Fig. 22-9

Kale

Kohlrabi

Brussels sprouts

Leaves

Stem

Wild mustard

Flowersand stems

Broccoli

Cauliflower

Flowerclusters

Cabbage

Terminalbud

Lateralbuds

Fig. 25-18

Close North American relative,the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearisDubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII0.4

millionyears

OAHU3.7

millionyears

KAUAI5.1

millionyears

1.3millionyears

MOLOKAIMAUI

LANAI

Fossils

• Give us real dates

• Show us what the “intermediate” features looked like

• “Missing Links” the intermediate species along lineages – e.g.. From apes to humans

• Very limited, chances of a species getting fossilized are low.

Fig. 22-3

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

Missing Links

Fig. 22-16

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)

(c) Dorudon (fully aquatic)

Pelvis andhind limb

Pelvis andhind limb

(d) Balaena (recent whale ancestor)

Fig. 13.4

Fig. 22-8

Hyracoidea(Hyraxes)

Sirenia(Manateesand relatives)

Moeritherium

Barytherium

Deinotherium

Mammut

Elephas maximus(Asia)

Stegodon

Mammuthus

Loxodontaafricana(Africa)

Loxodonta cyclotis(Africa)

010425.52434

Millions of years ago Years ago

Platybelodon

Fig. 22-8a

Elephas maximus(Asia)

Stegodon

Mammuthus

Loxodontaafricana(Africa)

Loxodonta cyclotis(Africa)

010425.52434

Millions of years ago Years ago

Platybelodon

Fig. 13.3

Fig. 22-15

Bristolia insolens

Bristolia bristolensis

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, SanBernardino County, California

Dep

th (

met

ers

)

0

2

4

6

8

10

12

14

16

18

1

2

3

3

3

1

2

44

Fossil Evidenceof Evolution in a group of Trilobites over time

Location and angle of head spines

Fig. 22-15c

Bristolia insolens

10

8

0

Dep

th (

met

ers)

4

Bristolia bristolensis

2

4

6

3

4

3

Vestigial Structures

• Come from an ancestral species

• No longer serve an function

• Are neutral traits, not harmful, and thus not “selected against” in origins of new species– Appendix– Hip bones in Pythons, Whales– Ear muscles in humans

backbone

pelvic girdle

coccyx (boneswhere manyother mammalshave a tail)

small boneattached topelvic girdle

thighboneattached topelvic girdle

Molecular Comparisons

• Counts mutations to an important gene

• “Conserved” genes mutate slowly, used to show distant relationships

• Can compare any living species, or fossil tissues that still have DNA

• Show how closely they are related

• Doesn’t show what intermediate species looked like

Fig. 13.5

Molecular clocks

• Useful comparisons of any living species • Uses date from fossil for when species

lineages separated• Compares mutations to common gene

between these species to show a rate of mutation in a gene

• Can make an estimate for species with that gene, that do not have a fossil record

• Gives an estimated date

Fig. 13.6

Embryology

• Animals only, especially the vertebrates

• The more closely related two species are the more similar their embryo will be for a longer period of development

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

Comparative embryology

Comparative embryology

Structures

• Homologous structures-– Show common ancestry– Derived from a common ancestral structure– May have specialized into different functions

Homologous Bones in Mammals

Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human WhaleCat Bat

Analogous Features• Have same functions ( by convergence)

• Do not have a common ancestry

• Are not derived from the same ancestral feature

Butterfly and Bird

• No bones in butterfly, not from common ancestor

• Structures not related

Convergence

• Not closely related

• Look similar due to adapting to similar habitat

Fig. 13.9b

Rate of evolution

• Gradualism- slow and constant changes build up over time to make new species.

• Punctuated equilibrium there are relatively brief ( in geologic time scale) periods with rapid change, followed by long periods with little change in species.– Follow periods of climate change and mass

extinctions

Fig. 13.2

Charles Darwin

Putting Darwin in the context of his time

Important people

• Linnaeus

• Lamarck

• Cuvier

• Malthus

• Lyell

• Wallace

Natural Theology• Belief that studying nature revealed divine

knowledge – arguments to prove the existence of God – without supernatural revelation.– Paley’s watchmaker argument– Intelligent design arguments of today

Used along with Christian Beliefs based on a literal view of the Genesis Story:

• Earth 6,000 yrs old• No new species• No physical changes (valleys, mountains)• Study, categorizing nature to reveal a divine

plan.

Linnaeus

• Studying biology to reveal a divine plan

• Developed modern taxonomy

• Made Binomials: Homo sapiens

• Based groupings on morphology

• Did not believe in evolution,

• Taxonomy data would later provide some of best evidence

His Purpose:

• The Earth's creation is the glory of God, as seen from the works of Nature by Man alone. The study of nature would reveal the Divine Order of God's creation, and it was the naturalist's task to construct a "natural classification" that would reveal this Order in the universe.

• He liked to say ' Deus creavit, Linnaeus disposuit, ' Latin for, "God created, Linnaeus organized".

Other accomplishments:

• Reversed Celsius’ thermometer – from 100 – melting and 0 boiling to today’s

• 0 – freezing, 100 boiling.

Still very early science:

• Also named (as real) in his taxonomy various mythological animals; including the troglodyte, satyr, hydra, and phoenix

• Included other human species from legends:– Homo ferus: four footed, mute & hairy– Juvenis lupinus - wolf boys

• Still use his method of classification into hierarchies and the binomial, not his actual taxonomy.

• He did classify humans as animals, and then as primates. Controversial for the time.

Cuvier

• Developed Paleontology– the study of fossils

• deeper the strata (layers) more dissimilar to current organisms

• Didn’t believe in evolution

• Thought strata relate to catastrophic events ( Noah’s flood etc.) and replacement by migration

Lamarck

• Got the genetics wrong

• Stressed acquired traits-(wrong)– Giraffes stretched their necks– Babies had longer necks

• But- said species evolved to be better suited to environment – right!

Fig. 13.1

Malthus

• British economist studied Paris after the revolution

• Limited resources

• Excess population growth

• Struggle to survive,

• competition among individuals

• Survival of the richest

Lyell

• British geologist.

• Following Hutton’s work

• Earth is old

• Valleys formed by erosion

• Mountains by uplifting

• Slow processes over long periods of time

Voyage of the Beagle

Galapagos Finches

• Specialization to different feeding sources may have diversified the species.

Isabela

Darwin

Wolf

Pinta

Marchena Genovesa

Fernandia

SantiagoBartolomé

Rabida

Pinzon

Baltra

Santa Cruz

Santa Fe

Tortuga

Española

San Cristobal

Floreana

Fig. 22-6

(a) Cactus-eater (c) Seed-eater

(b) Insect-eater

Fig. 22-12

(b) A stick mantid in Africa

(a) A flower mantid in Malaysia

Fig. 22-UN1

Observations

Over time, favorable traitsaccumulate in the population.

Inferences

and

Individuals in a populationvary in their heritable

characteristics.

Organisms produce moreoffspring than the

environment can support.

Individuals that are well suitedto their environment tend to leave

more offspring than other individuals

Fig. 22-UN2

Fig. 22-UN3

Evidence that Made Darwin think..

• The variation among organisms in a population• Biogeography – where species are found around

the globe• Fossil record• Comparative morphology – Linnaeus's

classification• Artificial Selection • Geology and the age of the earth• Malthus and economic theory• Lamarck’s theory and adaptations

Darwin and Human Evolution

• Published “Descent of Man” in 1871

• Wasn’t first to hypothesis our relation to apes

• caused more popular criticism of his general theory

• “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”