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Lecture #1 – Darwinian Evolution

Image of Darwin

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Key Concepts:

• Evidence for evolution• Darwin’s theory• The Modern Synthesis

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Spiritual vs. Intellectual

Different, but not necessarily in conflict

The human emotional experience The human intellectual experience

“The Bible tells us how to go to Heaven, not how the heavens go”Galileo

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Reality Check:The world’s major religions and the dominant

religion in the world’s four most populous countriesReligious Affiliation

World China India United States

Indonesia

Christian 33 8 6 82 13Muslim 21 2 14 2 77

Non-believers 14 50 1 12 2

Hindu 13 ~0 73 1 3

Other 12 32 6 1 4

Buddhist 6 9 1 1 1

Jewish ~0 ~0 ~0 2 ~0

SOURCE – National Geographic, December 2007

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There are many equally valid ways “to go to Heaven”

• We rely on our religious texts for moral, emotional and spiritual guidance

• We rely on science and other intellectual pursuits to gain knowledge about the natural world

There need be no conflict in these different ways of thinking and learning

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Images – species, population, community

Some preliminary definitions

• Species – individual organisms capable of mating and producing fertile offspring

• Population – a group of individuals of a single species

• Community – a group of individuals of different species

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Defining Evolution:

• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

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Image – finches on the Galapagos

Photographs by B

. Rosem

ary Grant/S

cience, 2006Historical Evidence: observed character

displacement Changes in beak size recorded over about 2 decades

after a natural migration event

Big-beaked invader

Resident species shifted to smaller beak size

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Image – rice

All of agriculture is based on human selection events

• The domestication of grass ~12,000 years ago

• Led to the first cultural shift in human civilizationNomadic hunter-gather

tribes villages based on agricultural production

• Other plants and animals as well….

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Artificial Selection – Brassica oleracea in all its forms

Image – cabbage, kale, cauliflower, broccoli, Brussels sprouts

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Images – different breeds of cattle and chickens

Farm Animals – different breeds

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Images – different breeds of cats and dogs

Cats and DogsA great dane is the same species as a toy poodle!

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Diagram – development of pesticide resistance due to use of insecticides

The development of pesticide resistance

• Resistance to insecticides, herbicides, antibiotics…..

• All natural responses to human generated changes in the environment

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Defining Evolution:

• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

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Images – fossils of plants and fish

The fossil record extends back BILLIONS of years

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Diagram – formation of sedimentary rocks with fossils embedded

Most form in marine sediments

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Images – other fossil substrates

Fossil substrates – can you think of others???

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Formation of sedimentary rocks is not uniform in time or space

Diagram – formation of sedimentary rocks with fossils embedded

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Critical Thinking

• The formation of sedimentary rocks is not uniform in time or space

• Why not???

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Critical Thinking

• The formation of sedimentary rocks is not uniform in time or space

• Why not???

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Formation of sedimentary rocks is highly dynamic

• Varies with geological activityTectonic movements, mountain building,

erosionVaries with climateRain, wind, freeze/thaw cycles, water

temperature – all affect erosion and sedimentation

• Varies with the depositional environmentFiner sediments in still water, coarser

sediments with more wave action or other energy

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Diagram – dynamic geological processes:tectonic movements, mountain building, erosion

The earth’s crust is very dynamic

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Formation of sedimentary rocks is highly dynamic

• Varies with geological activityTectonic movements, mountain building,

erosion• Varies with climate

Rain, wind, freeze/thaw cycles, water temperature – all affect erosion and sedimentation

• Varies with the depositional environmentFiner sediments in still water, coarser

sediments with more wave action or other energy

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Graph of benthic carbonates – analogous to climate change over the past 5 million years

Climate is naturally dynamic on a geological time scale

Benthic carbonates parallel atmospheric temperature changes

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Critical Thinking

• How could water temperature affect the formation of sedimentary rocks???

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Critical Thinking

• How could water temperature affect the formation of sedimentary rocks???

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Formation of sedimentary rocks is highly dynamic

• Varies with geological activityTectonic movements, mountain building,

erosion• Varies with climate

Rain, wind, freeze/thaw cycles, water temperature – all affect erosion and sedimentation

• Varies with the depositional environmentFiner sediments in still water, coarser

sediments with more wave action or other energy – WHY???

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Play with the “ocean”

• In high energy environments (waves) only the heaviest sediments can settleCoastal environments produce sandstones

• In off-shore environments (no waves) finer sediments can settleOff-shore environments produce siltstones,

slates, limestones…

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Diagram of different depositional environments

Sediment size depends on the energy level at the site of deposition

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Formation of sedimentary rocks is highly dynamic

• THUS sediments tend to be deposited in identifiable layers

• THUS organisms trapped in sediments form a time sequence The earliest organisms are in the bottom

layers and the most recent organisms in the upper layers

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Image – the Grand Canyon showing layers of sedimentary rock

The Grand Canyon – a time sequence

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Formation of sedimentary rocks is highly dynamic

• THUS sediments tend to be deposited in identifiable layers

• THUS organisms trapped in sediments form a time sequence The earliest organisms are in the bottom

layers and the most recent organisms in the upper layers

Dating these fossils reveals the history of change

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The geological time scale

Study the geological time scale – it’s the

history of life on earth!

Use a search engine to find the geological time

scale

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Of course the fossil record is incomplete!

• Organisms must be trapped in the right place under the right conditions – a rare event

• Fossils must survive geological processes such as subduction, metamorphosis and erosion

• Fossils must be found!Have you ever found a fossil???

• But what we do have is irrefutable evidence of change over time

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Fossil Evidence Shows Progression Over Time – new species….

Diagram – evolution of elephant lineages

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Diagram – limbs developing from bony fins in tetrapods

….new traits….

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Diagram – transition from bony fins to limbs

….transitional forms….

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Defining Evolution:

• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

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Comparative morphology – homologous structures are derived from a common ancestor

Diagram – forelimbs of various mammals showing identical bone structure with variation in bone size

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Diagram – similarities in the embryos of a wide variety of vertebrates

FishSalamanderTortoiseChickenPig Cow Rabbit Human

Strickberger, 1996

Stage of Development

Early

Later

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Images – orchid floral structure

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Comparative morphology – vestigial traits

• Structures that are physically or functionally reduced but clearly similar to functional structures in related organismsTiny limb bones in some snakes and aquatic

mammalsNon-flying wings in ostriches emus, kiwis,

penguinsBlind eyes in cave-dwelling animalsVestigial tails in humans

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Defining Evolution:

• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

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Biogeography – Darwin observed patterns of species distribution during his voyage on

the Beagle

Diagram – the voyage of the Beagle

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Image – modern and fossil sloths

Sloths – found only in South America, even though similar habitats exist on other continents

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Diagram of marsupial and eutherian mammals showing similar forms

Marsupials – almost restricted to Australia

…though convergent evolution has resulted in many similar eutherian mammals on other continents

Convergent evolution – similar traits in unrelated organisms that evolved under similar selection pressures….more later

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The Galápagos and other volcanic islands

Many closely related endemic species….that are similar to those found on the closest mainland

Darwin’s conclusion – species migrated and evolved new adaptations in their new home

Diagram of Darwin’s finch lineages

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Defining Evolution:

• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

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Image – frog in the center of a bromeliad

Uniformity and Diversity:same DNA, same ATP, same amino

acids, same membranes, same aerobic respiration….

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Critical Thinking

• What is the implication of this uniformity in the basic building blocks of life, even though there are many millions of organisms both extant and extinct???

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Critical Thinking

• What is the implication of this uniformity in the basic building blocks of life, even though there are many millions of organisms both extant and extinct???

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Defining Evolution:• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

Step 1: accepting that evolution occurs….Step 2:HOW???

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Hands On

• Let’s take a walk• Work in pairs• Find some living things• Think about uniformity and diversity• Meet back here in 20 minutes and be

prepared to discuss your thoughts• Record our discussion and type up a

summary to turn in tomorrow

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Defining Evolution:• A process of change over time• Cannot deny that this occurs• Evidence is overwhelming:

Historical – within the span of recorded human history

Fossils – the very long term geological recordComparative morphology and anatomyBiogeography – the geographic distribution of

speciesThe unity of life

Step 1: accepting that evolution occurs….Step 2:HOW???

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Timeline – the development of thought on evolution

Historical ContextThe development of ideas about biological evolution

and the age of the earth began in the 1700’s – Darwin was just the first to publish!

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Darwin’s voyage on the Beagle, 1831-1836…..publication of his theory, 1859

Map – the voyage of the Beagle

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Darwin’s Theory of Evolution by Natural Selection

based on observation + logical inference

• OBSERVATION #1 – all species have the reproductive potential for exponential population growth

• OBSERVATION #2 – populations tend to remain stable OBSERVATION #3 – environmental resources are limited INFERENCE #1 – excess of offspring leads to a struggle for

existence• OBSERVATION #4 – significant variation exists between

individuals of the same species• OBSERVATION #5 – some variation is heritable

INFERENCE #2 – individuals that are best adapted to their environment contribute more offspring to the next generation = differential reproductive success = Darwin’s natural selection

INFERENCE #3 – TIME X CHANGE = DIVERSITY

Don’t panic – this is just a summary slide for you to look at later

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Images – examples of high reproductive potential in various organisms

Observation #1: All species have the potential for exponential population growth

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Graphs – examples of actual population growth patterns

Observation #2: Populations tend to

remain stable(though sometimes within a fluctuating range)

not exponential

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Image – lynx chasing rabbit

Observation #3: Environmental resources are limited

food….

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Image – desert landscape

water….

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Images – various animals in habitat

habitat….

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Image – resource competition between aquatic plants

Inference #1: Excess offspring in a resource-limited environment leads to a

“struggle for existence”

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Observation #4: Variation exists in all natural populations

Diagram – natural variation in beetles

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Image – natural variation in plants

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Image – natural variation in mollusks

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Images – natural variation in humans

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Images – heritable variation in various animals

Observation #5: Some variation is heritable

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Image – polar bears fighting

Inference #2: Best adapted individuals reproduce the most

Differential Reproductive Success!!!

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Inference #3: Darwin’s Big One

Over long periods of time and many generations the incremental results of

differential reproductive success will lead to divergence between

populations in different environments and eventually to the development of

new species

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Image – orchid mantis

Key Conclusion

Small changes over long periods of time result in adaptations to different environments and to

the emergence of new species

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Same as previous

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Same as previous

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Images – additional cryptic animals; through slide #81

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Critical Thinking

• What other testable explanation is there for an insect or other animal that evades predation by mimicking its habitat???

• How else might this cryptic form and coloration benefit the animal???

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Critical Thinking

• What other testable explanation is there for an insect or other animal that evades predation by mimicking its habitat???

• How else might this cryptic form and coloration benefit the animal???

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Critical Thinking

• What other testable explanation is there for an insect or other animal that evades predation by mimicking its habitat???

• How else might this cryptic form and coloration benefit the animal???

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Diagram – mammal lineages

Darwin originally predicted gradual speciation from a common ancestor…..

• Now we know that abrupt changes are also possible

• Also, some gradual changes may not be recorded in the fossil record

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Images – more cryptic animals; same on next slide

Questions Remain• We don’t, and may never, know exactly

how life originated on this planet• But we do have a pretty good explanation

for how diversity developed and why diversity changes over timeConditions changeOrganisms adapt

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Questions Remain• We don’t, and may never, know exactly

how life originated on this planet• But we do have a pretty good explanation

for how diversity developed and why diversity changes over timeConditions changeOrganisms adapt

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The Modern Synthesis

• Darwin’s concepts of natural selection and differential reproductive success leading to adaptations and speciation

• Mendel’s work on heredity and hypothesis of a particulate method of hereditary transfer

• Microscopic revelation of chromosomes as that particle in the late 1800’s – early 1900’s

• Discovery of the structure of the DNA molecule in the early 1950’s

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The Theory of EvolutionA comprehensive body of knowledge that describes a known fact of nature

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Key Concepts:

• Evidence for evolution• Darwin’s theory• The Modern Synthesis

Questions???

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Hands On

• What are some selection pressures that might lead to adaptations???

• Think about what we collected earlier• Record our discussion and type up a

summary to turn in tomorrow