Chapter 22:Descent with

Modification - A Darwinian View of

Life

Essential Knowledge

1.a.1 – Natural selection is a major mechanism of evolution (22.2).

1.a.4 – Biological evolution is supported by scientific evidence from many disciplines, including mathematics (22.3).

Evolution The processes that have

transformed life on earth from its beginnings Change in genetic make-up over

time Gradual appearance of

biological diversity Illustrates science as a

PROCESS

Evolutionary Adaptation

An accumulation of inherited characteristics that enhance an organisms ability to survive and reproduce Involves populations – group of animals of same species that live in same geographic area

Pre-Darwinian Views

1. Greeks2. Fixed3. Catastrophism4. Hutton and Lyell5. Lamarck

Greek Philosophers

1. Plato - Organisms are already perfectly adapted to their environment

2. Aristotle - Organisms arranged on a “scale of life” from simple to complex

Fixed, unchanging Ladder of Life

Result: Greek No evolution Life is already perfect and doesn’t need to change

All the rungs on life's "ladder" are already occupied.

Fixed Species The creator had designed each and every species for a particular purpose.

Coincides with Old Testament

Says Earth is only5-6,000 yrs old (according to the Bible)

Result: Fixed Species

No Evolution! Created the viewpoint that all

species could be identified and named (Taxonomy).

A major factor in the Linnaeus classification system

Similarities showed pattern of creationism (not an evolutionary pattern)

Catastrophism Georges Cuvier

(1769-1832). Attempted to

relate fossils to current life

Paleontology started

Noticed: Deeper fossils were less similar

Catastrophism Idea Fossils were the remains of

species lost due to catastrophe No new species originated;

species could only be lost over time

Each rock/strata boundary represented a catastrophe

Catastrophe destroyed all/many species

Created a mass extinction Result – No evolution!

James Hutton Geologist Related living organisms and their changes to changes in the Earth

1795 - Gradualism Profound change is the cumulative product of slow, but continuous process

Result: Gradualism

Changes on the Earth were gradual, not catastrophic.

Gradual mechanisms change living organisms (and Earth)

Charles Lyell Geologist 1797 - 1875. Incorporated

Hutton’s gradualism into a theory called Uniformitarianism.

Uniformitarianism idea

Geological processes have operated at the same rate over the Earth’s history These processes are STILL occurring today

More comprehensive theory (involved past AND present)

Result: Uniformitarianism

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 over time

Jean Baptiste Lamarck

Published theory in 1809.

Theory - Life changed from simple to complex over time

Lamarck Fossils were the remains of past life forms

Used fossils to create of descent

Evolution did occur. His two mechanisms were incorrect

Mechanisms1. Use and Disuse -

Body parts used to survive become larger and stronger

Body parts not used to survive deteriorate.

Ex: giraffe (neck was constantly stretched to reach leaves)

Mechanisms2. Inheritance of Acquired Characteristics Modifications acquired by use/disuse were passed on to offspring

Ex: muscular arms (you work out and therefore your children will be muscular)

Problem w/ Lamarck He had no prior knowledge

of genetics (hadn’t been “discovered” yet)

Acquired traits are not transmitted offspring

Lamarck claimed animals have an innate drive to become more complex (not better adapted!)

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

Problem: timing (too fast!)

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).

Was a poor student Quit medical school (to become clergy man and ship naturalist)

Voyage of the Beagle

1831-1835: Trip was

used to ch

art coastl

ines

of Southern hemisp

here

Result: Voyage Became interested in

geographic distribution of species (why certain animals live where they do?)

Visited: Brazilian jungles, Galapagos islands, Argentina, Antarctica, Andes Mtns

Allowed him to formulate and support his ideas on Natural Selection

Galapagos Finches

Beaks and behaviors have adapted to specific foods available on specific islands

Island Tortoises

Neck lengths have adapted to foods on specific islands

Marine Iguanas

Adapted swimming/walking adaptations to be successful both in water and on land

Alfred Wallace - 1858

Wrote paper on natural slection

Ideas were identical to Darwin's.

Waited to publish (wrote to Darwin w/ ideas)

Result - July 1, 1858

Dual presentation of the Wallace-Darwin ideas to the Linnaean Society of London. Lyell presented

1859 – Darwin published (solo) the “Origin of Species”

Comment Darwin best remembered

for the theory because of his overwhelming evidence and because he published 1st! Wallace could have received credit for his ideas (but he idolized Darwin and wanted him to get the attention)

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 Most branches are dead ends!

99% of all species are extinct

“The Origin of Species”

Documented the occurrence of evolution

Suggested that the mechanism for evolution was Natural Selection.

Conclusion: Biological diversity was/is the product of evolution

Focused on diversity of organisms Includes: geographic distribution, adaptations, origins

Two points:1) Ancestral descendants2) Natural selection is mechanism for evolution

“The Origin of Species”

The Theory of Evolution

Based upon 5 major facts/observations Helps to devise 3 evolutionary inferences

Evolution: The Facts:

Fact 1 - All species reproduce themselves Until

resources limit this growth

The Facts, cont: Fact 2 –

Most populations are normally stable in size

Fact 3 – Natural Resources are limited (finite).

Inference 1 Use Facts 1, 2, 3 The large number of offspring must compete for the limited resources

Result - Most offspring will die!

More Facts Fact 4 –

No two individuals in a population are exactly alike

Fact 5 – Variation is inherited

Inference 2 Use Facts 4, 5 Those individuals whose inherited characteristics fit them best to their environment will survive and reproduce!

Inference 3 Use Facts 4, 5 Offspring inherit the favorable characteristics

Populations shift over time as the favorable characteristics accumulate

Thomas Malthus Demographer (geographic distribution and population growth)

Helped Darwin to develop these inferences

Nature Nature: Food, shelter,

disasters, climate Determines which

characteristics are favorable Favors some, while filtering

others Determines who will

survive! Result - “Natural Selection”

Artificial Selection

When man determines the characteristics that survive and reproduce

Result - the various breeds of animals and plants we’ve developed. Genetic engineering!

Evolution Success Measured

By: Survival rate Reproductive rate (success)

Whoever lives long enough and has kids is the “winner” in evolution.

Requirements for Natural Selection

In order for Natural Selection to work, you must have: Long periods of time Variations within a population

Subgroups of Natural Selection

1. Populations are the units of Evolution (NOT individuals)

2. Only inherited characteristics can evolve (traits passed from parent to offspring)

3. Natural selection is always operating (based upon environmental factors)

Comment Some acquired characteristics may allow a species to evolve "outside" of natural selection

Ex: culture, learning, diet, exposure to mutagens

Nature vs. nurture

Visible Signs of Evolution

1. Biogeography2. Fossils3. Taxonomy4. Comparative Anatomy5. Comparative Embryology

6. Molecular Biology

Biogeography The geographical distribution of species

Problem: Species mixtures on islands

Marsupials in Australia

Biogeography Closely/Evolutionarily-related

species tend to be found in the same geographic region

However, the same niches (in differing regions of the world) are usually occupied by species that may have evolved similar adaptations – but are DIFFERENT species Ex: sugar glider and flying squirrel

**Both have adapted similar adaptations (skin flaps) but are NOT closely related to each other. They have evolved this adaptation independently

** Islands often contain ENDEMIC species (species that are found NO WHERE ELSE in the world!)**Why? Islands are a perfect example of how geography influences evolution

Evolution Viewpoint

Biogeographical patterns reflect descent from the ancestors that colonized the area

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: Fossils1. Fossilization is a rare event

2. Only hard parts fossilize well

3. Problem in finding fossils

4. Interpretation.5. “Missing links”

Taxonomy Science of

Classification.

Using various characteristics – group organisms by like characteristics

Main Categories Domain Kingdom Phylum or Division Class Order Family Genus Species

Comparative Anatomy

1. Homologous Structures - Common "building plan” with divergent functions

Mammal forelimbs

Comparative Anatomy

2. 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

Comparative Embryology

Problem - closely related organisms go through similar stages in their embryonic development

Ex: Gill pouches in vertebrates

All animals go through these stages of development!!

Evolution Viewpoint

Ontogeny is a replay of Phylogeny. (Development reflects descent)

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 ancestral DNA. The closer the relationship, the more similar the DNA sequences should be.

Summary Recognize viewpoints of evolution

preceding Darwin, and identify their main points and characteristics.

Identify the assumptions, inferences and outcomes of Darwin's Theory of Natural Selection.

Recognize the signs of the process of evolution through the mechanism of natural selection.