Descent with Modification

Chapter 22

Rise of Modern Biology

A. Pre-Darwin Ideas Geology Larmark

B. Charles Darwin Darwin Wallace

Evolution: Change over time A new era of biology began when Charles

Darwin published On the Origin of Species by Means of Natural Selection

He made two points in The Origin of Species: Today’s organisms descended from ancestral

species Natural selection provided a mechanism for

evolutionary change in populations Natural Selection: individuals with certain

heritable traits leave more offspring EvolutionaryAdaptations : characteristics

that enhance survival

Pre-Darwin Ideas Aristotle believed that all living forms could

be arranged on a ladder (scala naturae) of increasing complexity with every rung taken with perfect, permanent species.

In the 1700’s, the dominant philosophy, natural theology the Creator had designed each species for a purpose.

Carolus Linnaeus, a Swedish botanist, developed taxonomy, a system for naming species and grouping species into a hierarchy of increasingly complex categories

Geology and the Gift of Time Idea that the earth is young

(6000yrs)never go anywhere Geologists can’t get young earth Georges Cuvier (1769-1832) James Hutton (1726-1796) Charles Lyell (1797-1875)

Georges Cuvier(1769-1832) Paleontology the study of fossils, Documented the succession of fossil

species in the Paris Basin Recognized that extinction had been a common

occurrence in the history of life Catastrophism instead of evolution that

boundaries between strata were due to local flood or drought that destroyed the species then present Later, this area would be repopulated by

species immigrating from other unaffected areas

James Hutton (1726-1796) Scottish geologist Proposed that the diversity of land

forms (e.g., canyons) could be explained by mechanisms currently operating

A theory of gradualism profound change results from slow, continuous processesSame forces have always been there

erosion

Strata of sedimentary rock at the Grand Canyon

From 1.25 BY to 250my

Charles Lyell (1797-1875)

Scottish, friend of Darwin, good writer Proposed a Theory of Uniformitarianism

The geological processes had not changed throughout Earth’s history

Same processes are operating today as in the past

Jeane Baptiste Lamarck (1744-1829) 1st comprehensive idea of evolution Came up with the mechanisms for

evolution Use and Disuse Inheritance of Acquired Characteristics Stressed adaptation

Influence on Darwin Hutton’s and Lyell’s observations and

theories had a strong influence on Darwin First, if geological changes result from

slow, continuous processes, rather than sudden events, then the Earth must be far older than the 6000 years

Second, slow and subtle processes persisting for long periods of time can add up to substantial change

The historical context of Darwin’s life and ideas

Charles Darwin Son of a wealthy physician Sent to become one Decided it was not for him Entered the clergy studied natural theology-imprint

of God in nature Professor recommends to go on a trip around the

world Journey on the HMS Beagle

Mission was to chart the poorly known stretches of the South American coastline

He collected thousands of specimens of the exotic and diverse flora and fauna of South America

Darwin’s Observations The plants and animals of South America were very distinct

from those of Europe Organisms from temperate regions of South America were

more similar to those from the tropics of South America than to those from temperate regions of Europe

South American fossils more closely resembled modern species from that continent than those from Europe.

While on the Beagle, Darwin read Lyell’s Principles of Geology Lead him to doubt the church’s position that the Earth was

static and only a few thousand years old He came to the conclusion that the Earth was very old and

constantly changing By 1840, he had worked out the major features of a theory

based on his observations from his journey Was hesitant to publish his ideas and was scared of the

backlash that they would cause It wasn’t until he heard that another scientist, Alfred Russell

Wallace, was developing a theory very similar to his own that he decided to publish.

Darwin and Wallace

Alfred Wallace independently developed a theory of evolution by natural selection

Both share the idea of Natural selection as a Mechanism of evolution

“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.”-Charles Darwin

Information that influenced Darwin

Charles Lyell geologist proposed that the Earth was very old and had slowly been changing for millions of years

Thomas Malthus economist social problems as a result of the exponential growth of the human population

Artificial selection by breeders

Artificial Selection

Darwin’ Two Main Ideas

Descent with Modification Natural Selection and Adaptation

Descent with Modification All present day organisms are related through

descent from unknown ancestors in the past Descendents of these ancestors accumulated

diverse modifications or adaptations that fit them to specific ways of life and habitats

The history of life is like a tree with multiple branches from a common trunk

Closely related species, the twigs of the tree, shared the same line of descent until their recent divergence from a common ancestor

This evolutionary tree of the elephant family is based on evidence from fossils.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Darwin’s Key Observations

1. Fossils & fossil records show that organisms simpler complex

2. Overproduction of offspring3. Limited supply of resources in

an environment4. Survival in a limited

environment depends in part on features inherited from parents

Natural Selection

Individuals whose inherited characteristics adapt them best to their environment are most likely to survive and reproduce

Basic Mechanism of Evolution Natural Selection

Natural Selection and Adaptation Variations exist Many of these

variations are heritable

Camouflage Evolutionary Adaptation A heritable trait that increases an

organism’s likelihood of surviving and reproducing in its environment

Evolution by Natural Selection Natural selection is the differential

reproductive success of among individuals Variations exist; some represent adaptive

traits that increase reproductive success Many of these are heritable Over time, this can increase the

adaptation of organisms to their environment

Environmental changes may result in adaptation of a species to these new conditions.

Fitness Individual organisms are

selectedPopulations evolve!Remember, individuals live or

die. They do not evolve!

Natural Selection in Action

Biston betularia : peppered moth

Evolution of Drug Resistant HIV

3TC interferes w/ reverse transcriptase

Evolution of Drug Resistance A drug does not create a resistant

pathogen It selects for existing resistant pathogens

And so with evolution: Evolution does not create novel life forms Nature selects from existing variants

Evidence of Evolution

Evidence of Evolution

1. Fossil Records2. Comparative Anatomy3. Embryonic Structures4. DNA Homology5. Biogeography

Fossils Remains, traces or imprints of

an organism preserved in the earth’s crustImprintMoldCastPetrified

Fossil Records1. Fossils & the order in which they

appear in layers of rocks2. Fossil records show that animals &

plants have appeared in a historical sequence, fossils found in rocks of different ages differ because life on Earth has changed through time

Each Layer represents a particular time period

Comparative Anatomy The comparison of body structures in

different species Homologous Structures Analogous Structures Vestigial Structures

Ex: common descent evident in anatomical similarities between species in the same taxonomic group

Homologous Structures

Structures that are similar & have been derived from a common ancestor, but have been adapted to different functions.

ex: humans, cats, whales, bats all mammals

Whales’ flipper does not have the same function as a bat’s wing

Homologous Structures

Analogous Structures Body parts similar in function but

have different structuresEx: wings of insects and birds

Vestigial Structures

Body parts reduced in size & appear to serve no function

Embryonic Structures Embryos of closely related

organisms often have similar stages in development

DNA Homology

Comparison of genes and proteins shows the relationships between species

Biogeography Closely related species tend to be found in the

same region The geographical distribution of species only makes

sense in light of evolutionary past

What are specific examples? Marsupial Mammals in Australia Finches in Galapagos Fruit flies in Hawaii

Different geographic regions, different mammalian “brands”