Objectives: 1)Describe how natural variation is used in artificial selection. 2)Explain how natural...
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Transcript of Objectives: 1)Describe how natural variation is used in artificial selection. 2)Explain how natural...
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