15-3Darwin Presents

His CaseObjectives:

1) Describe how natural variation is used in artificial selection.2) Explain how natural selection is related to species’ fitness.3) Identify evidence Darwin used to present his case for

evolution.4) State Darwin’s theory of evolution by natural selection.

Publication of On the Origin

of Species

Darwin’s ideas challenged fundamental scientific beliefs

Discussed his work with friends

Shelved his manuscript for years

Told his wife to publish it when he died

Publication of On the Origin

of Species (cont’d) 1858 Alfred Russel

Wallace wrote an essay summarizing his thoughts on evolutionary change and sent it to Darwin

This caused Darwin to want to publish his findings

Publication of On the Origin

of Species (cont’d) 1859 Darwin published On

the Origin of Species Suggested a

mechanism for evolution (natural selection)

Caused a sensation

Blue Ticket Question

What event motivated Darwin to publish his ideas?

Darwin received Wallace’s essay

Play: http://www.sciencechannel.com/games-and-interactives/charles-darwin-game/

Blue Ticket Answer

Inherited Variation and

Artificial Selection

1 of Darwin’s most important insights was that members of each species vary from 1 another in important ways

Inherited Variation and

Artificial Selection (cont’d) Variation exists both

in nature and on farms

Heritable variation—differences that are passed from parents to offspring Happened in the

wild Revolutionary idea

Inherited Variation and

Artificial Selection (cont’d) Animal breeders use heritable variation (genetic

variation) to improve crops and livestock Selected only the organism that had the desirable

traits to reproduce (artificial selection)

Inherited Variation and

Artificial Selection (cont’d)

In artificial selection, nature provided the variation, and humans selected those variations that they found useful Has produced many diverse domestic animals and crop

plants

Evolution by Natural

Selection Darwin compared

processes in nature to artificial selection

Developed a scientific hypothesis to explain how evolution occurs

Greatest contribution

The Struggle for

Existence Struggle for existence: members of each species compete

regularly to obtain food, living space, and other necessities of life

Predators—catch more prey if they are faster, etc. Prey—survive if they are better protected

Survival of the Fittest

A key factor in the struggle for existence is fitness Fitness: the ability

of an individual to survive and reproduce in its specific environment

Survival of the Fittest

(cont’d) Darwin suggested that

fitness is the result of adaptations Adaptations: any

inherited characteristic that increases an organism’s chance of survival

Successful adaptations allow organisms to become better suited to their environment to survive and reproduce

Survival of the Fittest

(cont’d) Adaptations can be

Anatomical (structure)

Characteristics Physiological

processes (functions)

Behavior Live Hunt

Survival of the Fittest

(cont’d) The concept of fitness was

central to the process of evolution by natural selection

Survival of the fittest Organisms that are not well

suited to their environment Die Leave few offspring

Organisms that are better suited to their environment Survive Reproduce more

successfully

Survival of the Fittest

(cont’d) In natural selection

Only certain individuals of a population produce new individuals

The traits being selected contribute to an organism’s fitness in its environment

Takes place without human control or direction

Survival of the Fittest

(cont’d) Over time, natural

selection results in changes in the inherited characteristics of a population These changes

increase a species’ fitness in its environment

Survival of the Fittest

(cont’d) Cannot be seen

directly Observed as

changes in a population over many successive generations

Blue Ticket Question

What did Darwin mean when he described certain organisms as “more fit” than others?

Organisms that are better suited to survive in

their environment and pass their traits on to the next generation

Blue Ticket Answer

Descent with Modification

Darwin suggested that over long periods of time, natural selection produces organisms that have different structures or occupy different habitats Species today look

different from their ancestors

Descent with Modification

(cont’d)

Descent with modification: each living species has descended, with changes, from other species over time Implies that all living organisms are related to one

another

Descent with Modification

(cont’d)

Common descent: all species—living and extinct—were derived from common ancestors

Evidence of Evolution

Darwin argued that living things have been evolving on Earth for millions of years.

Evidence for this process Fossil record Geographical distribution of living species Homologous structures of living organisms Embryology (similarities in early development)

The Fossil Record

Darwin suggested that Earth was many millions of years old

Countless species had come into being, lived for a time, and then vanished

The Fossil Record

(cont’d) Scientists document

the fact that life on Earth has changed over time by comparing fossils from older rock layers with fossils from younger layers

Fossils point out uncertainties in our understanding of exactly how some species evolved

Geographic Distribution of Living

Species

Darwin’s theory of descent with modification made scientific sense of why he sometimes saw different animals that had similar anatomies and behaviors

Geographic Distribution of

Living Species (cont’d)1) Species now living on

different continents had each descended from different ancestors

2) Some animals on each continent were living under similar ecological conditions and were exposed to similar pressures of natural selection

3) Different animals ended up evolving certain striking features in common

Homologous Body

Structure Homologous structures: structures that have different

mature forms but develop from the same embryonic tissues Provides strong evidence that all 4-limbed vertebrates have

descended, with modifications, from common ancestors

Homologous Body Structure

(cont’d) Similarities and

differences help biologists group animals according to how recently they last shared a common ancestor

Homologous Body Structure (cont’d)

Vestigial organs: organs so reduced in size that they are traces of homologous organs in other species

The presence of a vestigial organ may not affect an organism’s ability to survive and reproduce Natural selection would

not cause the elimination of that organ

Similarities in Embryology

The early stages (embryos) of many animals with backbones are very similar

The same groups of embryonic cells develop in the same order and similar patterns to make the tissues and organs of all vertebrates Make homologous

structures

Blue Ticket Question

What are homologous structures?

Homologous structures are structures that

have different mature forms but develop from the same embryonic tissue

Blue Ticket Answer

Organisms

Differ, and some variation is heritable Make more offspring than can survive and many that do

survive do not reproduce Compete for limited resources Have different advantages and disadvantages in the

struggle for existence Pass their heritable traits to their offspring (natural

selection) Are descended with modification from ancestral species

that lived in the distant past Evolved from common ancestors (tree of life)

Summary of Darwin’s Theory

Strengths and Weaknesses of

Evolutionary Theory Scientific advances

have confirmed and expanded most of Darwin’s hypotheses

Evolutionary theory continues to change as new data are gathered and new ways of thinking arise

15-3 Exit Ticket