Chapter 22 Descent with Modification:

A Darwinian View of Life

Question?

How did the diversity of life

originate?

Through the process of

Evolution.

Evolution

The processes that have

transformed life on earth

from its beginnings to today's

diversity.

Evolution is the most

pervasive principle in

biology.

Theory vs theory

Theory

Hypothesis

supported

repeatedly by

data

Makes testable

predictions

theory

Layman’s and

TV use of the

word

Confused with

hypothesis in

Science

Examples of Theory

Cell Theory

Big Bang Theory

Atomic Theory

Theory of Gravity

Theory of Evolution

Evolution

Has itself "evolved" or changed

over time.

Illustrates “Science as a

Process”.

Students should be able to give

the main points of several views.

Pre-Darwinian Views

1. Greeks

2. Fixed Species

3. Catastophism

4. Hutton and Lyell

5. Lamarck

Greek Philosophers

1. Plato - Organisms are

already perfectly adapted to

their environments.

2. Aristotle - Organisms

arranged on a “scale of life”

from simple to complex.

Result

No evolution.

Life is already perfect and

doesn’t need to change.

All the rungs on life's "ladder"

are already occupied.

Fixed Species Concept

The creator had designed

each and every species for a

particular purpose.

Result

No evolution.

Created the viewpoint that all

species could be identified

and named (Taxonomy).

A major factor in the

Linnaeus classification

system.

Catastrophism

Georges Cuvier

(1769-1832).

Attempted to

relate fossils to

current life.

Theory

Fossils were the remains of

species lost due to

catastrophe.

No new species originated;

species could only be lost

over time.

Result - No evolution.

James Hutton

1795 - Gradualism

Profound change is the

cumulative product of slow,

but continuous processes.

Result

Changes on the earth were

gradual, not catastrophic.

Charles Lyell

1797 - 1875.

Incorporated

Hutton’s

gradualism into a

theory called

Uniformitarianism.

Uniformitarianism

Geological processes have

operated at the same rate

over the Earth’s history.

Result

The Earth must be VERY old.

(much older than 6000 years

of the fixed species concept).

Idea that slow and subtle

processes can cause

substantial change.

Jean Baptiste Lamarck

Published

theory in 1809.

Theory - Life

changed from

simple to

complex over

time.

Lamark

Fossils were the remains of

past life forms.

Evolution did occur.

Mechanisms

1. Use and Disuse -

Body parts used to survive

become larger and stronger.

Body parts not used to survive

deteriorate.

Mechanisms

2. Acquired Characteristics

Modifications acquired by

use/disuse were passed on to

offspring.

Problem

No knowledge of genetics.

Acquired traits are not

transmitted offspring.

Lamarck’s Credits

Did suggest correctly the role

of fossils in evolution.

Did suggest that adaptation

to the environment is a

primary product of evolution.

Thomas Malthus

Essay on human population

growth in 1798.

Disease, famine, homelessness,

and war are inescapable because

human populations grow faster

than food supplies.

Darwin read Malthus.

Charles Darwin

Father of the

modern theory

of evolution.

Theory -

Descent with

Modification.

Darwin's Background

Trained as a Naturalist (after

trying religion and medicine).

Voyage of the Beagle

Result

Darwin's training and travel

opportunities allowed him to

formulate and support his

ideas on Natural Selection.

Galapagos Finches

Alfred Wallace - 1858

Paper on Natural

Selection

identical to

Darwin's ideas.

Result - July 1, 1858

Dual presentation of the

Wallace-Darwin ideas to the

Linnaean Society of London.

Darwin - 1859

Publication of

"The Origin of

Species”

Comment

Darwin best remembered for

the theory because of his

overwhelming evidence and

because he published.

Homework

Read Chapter 22 (Hillis – 15)

Chapter 20 – today

Exam 2 – March 19

AP Exam enrollment???

Chapter 22 – Wed. 3/20

Darwinian View

History of life is like a tree

with branches over time from

a common source.

Current diversity of life is

caused by the forks from

common ancestors.

Example

“The Origin of Species”

Documented the occurrence

of evolution.

Suggested that the

mechanism for evolution was

Natural Selection.

Observations: Observation 1 – Members of a

population often vary greatly in their traits.

.

Observation 2

Traits are inherited from

parents to offspring.

Observation 3

All species are

capable of

producing

more offspring

than their

environment

can support.

Observation 4

Owing to lack of food or

other resources, many of

these offspring do not

survive.

Inference 1

Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.

Inference 2

This unequal ability of

individuals to survive and

reproduce will lead to the

accumulation of favorable

traits in the population over

generations.

Nature

Determines which

characteristics are favorable.

Determines who survives.

Result - “Natural Selection”

Natural Selection

in action

Artificial Selection

When man determines the

characteristics that survive

and reproduce.

Result - the various breeds of

animals and plants we’ve

developed.

Ex - Mustard Plant

Original Cultivars

Evolution Success

Measured By

Survival

Reproduction

Whoever lives long enough

and has kids is the “winner”

in evolution.

Requirements

In order for Natural Selection

to work, you must have:

Variations within a population.

Long periods of time (according

to Darwin).

Subtleties of

Natural Selection

1. Populations are the units of

Evolution.

2. Only inherited characteristics

can evolve.

Comment

Acquired characteristics may

allow a species to evolve

"outside" of Natural Selection.

Ex: culture, learning

Evidences for Evolution

Direct observation of evolutionary changes.

Fossils

Homology

Convergent Evolution

Biogeography

Molecular

Direct Observations

Color patterns in guppies

Drug resistant HIV

Beak size in Birds

PitX1 gene

Others

Color Pattern in Guppies

Field Experiment (see text for full

details)

Changed the selection pressure

on male guppies

Result – color pattern change in

15 generations (22 months).

HIV Drug Resistance

Drug resistance strains

selected for by treatments

Result – resistant strains

became 100% dominant in 4-5

weeks.

Beak Size

Field Study – measured the beak size of all birds in a population over several years.

Result – drought and food competition changed beak size.

Fossils

Relics or impressions of

organisms from the past.

Problem:

Show changes over time from

simple to complex.

Many fossils don't have

descendants.

Evolution Viewpoint

Life has changed over time.

Many species failed to survive and became extinct.

Comments

1. Fossilization is a rare event.

2. Only hard parts fossilize well.

3. Problem in finding fossils.

4. Interpretation.

5. Missing Links.

Homology

Homologous

Structures -

Common

"building

plan” with

divergent

functions.

Mammal forelimbs

Problems

Vestigial Organs

- Rudimentary

structures of

marginal, if

any, use.

Whale Legs

Human Example

Evolution Viewpoint

Remodeling of ancestral

structures as their functions

or adaptations changed.

Homology in Embryos

Problem - closely related

organisms go through similar

stages in their embryonic

development.

Ex: Gill pouches in

vertebrates

Evolution Viewpoint

Ontogeny is a replay of

Phylogeny.

(Development reflects descent)

Development reflects inheritance

of common control genes.

Convergent Evolution

Unrelated organisms show

similar adaptations.

Cause – lived in a similar

environment with similar

selection pressures.

Biogeography

The geographical distribution

of species.

Problem:

Species mixtures on islands

Marsupials in Australia

Evolution Viewpoint

Biogeographical patterns

reflect descent from the

ancestors that colonized that

area.

Molecular Biology

Study of Evolution at the

DNA or protein levels.

Problem - related species

have similar DNA sequences.

Evolution Viewpoint

Related species share a

common ancestrial DNA.

The closer the relationship,

the more similar the DNA

sequences should be.

Summary

Darwin's ideas now a "Theory”.

Predictions of a Theory are

tested by experiments and

observations.

Be familiar with the pre-Darwin

views of evolution.

Summary

Know Darwin’s “observations”

and “inferences”.

Be able to discuss the various

evidences of Darwinian

evolution.