What is science and how is it done?

• What is science? - Science is the systematic investigation of phenomena

• How is it carried out?- The SCIENTIFIC METHOD is the

systematic process by which such investigations are conducted

• Make an observation• Ask questions about causes• Develop testable hypotheses• Make predictions based on

hypothesis• Perform experiments to test

hypothesis

Scientific Method

We need repeated observations…replicates!

Select 1 marble = blueAssumption: all marbles are blue

Select 10 marbles - 3 marbles blueAssumption: 30% of marbles are blue

Sampling error can result from too few observations!

A Case Study in Scientific Inquiry: Investigating Mimicry in Snake Populations

Observation:1. Dangerous creatures have warning coloration2. Benign creatures mimic the dangerous

Question: Why?

Hypothesis: Mimicry evolved in harmless species as an evolutionary adaptation that reduces their chances of being eaten (Henry Bates)

Fig. 1-25

South Carolina

North Carolina

Key

Scarlet kingsnake (nonpoisonous)

Scarlet kingsnake (nonpoisonous)

Eastern coral snake (poisonous)

Range of scarletkingsnake onlyOverlapping ranges ofscarlet kingsnake andeastern coral snake

Field Experiments with Artificial Snakes

• Experimental Design – fake snakes– An experimental group resembling kingsnakes – A control group resembling plain brown snakes

• Equal numbers of both types were placed at field sites, including areas without poisonous coral snakes

• After four weeks, the scientists retrieved the artificial snakes and counted bite or claw marks

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

A Case Study in Scientific Inquiry: Investigating Mimicry in Snake Populations

Hypothesis: Mimicry evolved in harmless species as an evolutionary adaptation that reduces their chances of being eaten (Henry Bates)

Hypotheses for this experiment:H1: The ringed snakes will be attacked less frequently in the geographic region where coral snakes were found

Null Hypothesis H0: There will be no difference

Fig. 1-26

(a) Artificial kingsnake

(b) Brown artificial snake that has been attacked

Fig. 1-27

Artificial kingsnakes

Brownartificial snakes

83% 84%

17% 16%

Coral snakesabsent

Coral snakespresent

Perc

ent o

f tot

al a

ttac

kson

arti

ficia

l sna

kes

100

80

60

40

20

0

RESULTS

Fig. 1-25

South Carolina

North Carolina

Key

Scarlet kingsnake (nonpoisonous)

Scarlet kingsnake (nonpoisonous)

Eastern coral snake (poisonous)

Range of scarletkingsnake onlyOverlapping ranges ofscarlet kingsnake andeastern coral snake

A Case Study in Scientific Inquiry: Investigating Mimicry in Snake Populations

Hypotheses for this experiment:H1: The ringed snakes will be attacked less frequently in the geographic region where coral snakes were found

Null Hypothesis H0: There will be no difference

Result: The prediction is upheld. The null hypothesis is not supported, the hypothesis is not rejected.

Limitations of Science

• repeatable• peer review• Old science is replaced by new science when

there is a huge mountain of evidence, not before.

• Science cannot support or falsify supernatural explanations, which are outside the bounds of science

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Theories in Science

• In the context of science, a theory is:– Broader in scope than a hypothesis– General, and can lead to new testable hypotheses– Supported by a large body of evidence in

comparison to a hypothesis– Vetted

– EXAMPLE: Evolution – the central unifying theory of Biology and one of the central theories of Geology

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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. 22-2

American Revolution French Revolution U.S. Civil War1900185018001750

1795

1809

1798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.

Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)

Hutton (gradual geologic change)

Lyell (modern geology)

Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

Big new ideas occur from many smaller breakthroughs

Fig. 22-5

NORTHAMERICA

EUROPE

AFRICA

AUSTRALIA

GREATBRITAIN

SOUTHAMERICA

ATLANTICOCEAN

PACIFICOCEAN Cape of

Good Hope

Tierra del FuegoCape Horn

TasmaniaNewZealand

Ande

sEquator

TheGalápagosIslands

Pinta

MarchenaGenovesa

SantiagoDaphneIslands

PinzónFernandina

IsabelaSan

Cristobal

SantaFe

SantaCruz

Florenza Española

Fig. 22-6

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

(b) Insect-eater

Evolution

• Evolutionary change is based on the interactions between populations and their environment

• A population is the smallest unit that can evolve– Individuals are

selected– Populations evolve

Fig. 22-12

(b) A stick mantid in Africa

(a) A flower mantid in Malaysia

Organisms are adapted to their environments – How does this happen?

Evolution via Natural Selection

• Over production: Organisms produce more offspring than can survive

• Limited Resources: There usually isn’t enough to go around.

Observations

Fig. 22-11

Sporecloud

Evolution via Natural Selection

• Variation:– Individuals vary

extensively (phenotype)

• Inheritance of Variation: – Much of this

morphological variation is inherited (genotype)

Observations

Fig. 22-10

Evolution via Natural Selection

• Struggle for existence: production of more individuals than can be supported leads to competition for recourses

Inference #1

Evolution via Natural SelectionInference #2

• Survival of the best adapted: Individuals with traits that give them an advantage in the struggle for limited resources will survive. These individuals are more likely to leave offspring than individuals that are less fit

Evolution via Natural SelectionInference #3

• Accumulation of adaptations:The unequal ability of individuals to survive and reproduce will lead to a gradual change in populations

To sum up…

1. Individuals within species vary (phenotypic variation)

2. Some of this variation is heritable (genetic variation)

3. Survival and/or reproduction are non-random (natural selection)

The individuals that survive & reproduce the most are those with variations most suited to their environment

Hawaiian honeycreepers

Evolution is supported by an overwhelming amount of scientific evidence – argued for 250+years

• New discoveries continue to fill the gaps identified by Darwin in The Origin of Species

• Direct evidence – in the lab and in the field• Fossil Record • Molecular• Homology• Convergent Evolution• Ontogeny

Fig. 22-9

Kale

Kohlrabi

Brussels sprouts

Leaves

Stem

Wild mustard

Flowersand stems

Broccoli

Cauliflower

Flowerclusters

Cabbage

Terminalbud

Lateralbuds

DE

Fig. 22-3

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

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)

Fossils

Hox gene 6 Hox gene 7 Hox gene 8

About 400 mya

Drosophila Artemia

Ubx

Molecular evidence includes: Direct sequence similarityRegulatory genes

Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human WhaleCat Bat

Morphology: Homologous Structures in mammals

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

Morphology: Ontogeny

Fig. 25-19b

Chimpanzee fetus Chimpanzee adult

Human fetus Human adult

Morphology: Ontogeny

Fig. 22-20

Sugarglider

Flyingsquirrel

AUSTRALIA

NORTHAMERICA

Convergent Evolution

Fig. 25-24

(a) Patch of pigmented cells

Opticnerve Pigmented

layer (retina)

Pigmented cells(photoreceptors)

Fluid-filled cavity

Epithelium

Epithelium

(c) Pinhole camera-type eye

Optic nerve

Cornea

Retina

Lens

(e) Complex camera-type eye

(d) Eye with primitive lens

Optic nerve

CorneaCellularmass(lens)

(b) Eyecup

Pigmentedcells

Nerve fibers Nerve fibers

The pace of scientific change