Transcript Chapter 13 Section 1

Chapter 13 Section 1
THE THEORY OF NATURAL SELECTION
Grade 10 Biology
Spring 2011
Objectives
 Identify several observations that led Darwin to
conclude that species evolve
 Relate the process of natural selection to its
outcome
 Summarize the main points of Darwin’s theory of
evolution by natural selection as it is stated today
 Contrast the gradualism and punctuated
equilibrium models of evolution
Bell Ringer
 Write down what you already know about evolution
Biography of Darwin
 Darwin was a poor student,
disinterested in subjects his father
wanted him to engage in
 Attended medical school but was
repelled by surgeries and often
skipped lectures
 Was often found outdoors collecting
biological specimens
 Completed a degree in theology but
was interested in natural sciences
Biography of Darwin
 In 1831, Darwin was recommended for a position as
a naturalist on the HMS Beagle
Science Before Darwin
 Idea that each species is a divine creation that exists,
unchanging, as it was originally created
 Scientists had begun to seek to explain the origins of
fossils


Tried to explain their observations by altering traditional
explanations of creation
Others proposed various mechanisms to explain how living
things change over time
Science Before Darwin
 Lamarck’s theory
 Over the lifetime of an individual, physical features increase in
size because of use or reduce in size because of disuse
 These changes are then passed on to offspring
 Is incorrect, but correctly pointed out that change in species is
linked to “physical condition of life”
Darwin’s Observations
 Read Lyell’s book Principals of Geology, that
proposed that the surface of the Earth changed
slowly over many years
 Visited different places, where he saw things that he
thought could be explained only by a process of
gradual change

Extinct Armadillo fossils similar but not identical to present
species
Darwin’s Observations
 Galapagos Islands
 Many plants and animals resembled those of coast
 Hypothesized that ancestors of Galapagos species migrated to
islands from South America long ago and changed after they
arrived

Called it decent with modification- evolution
Growth of Populations
 Malthus
 Wrote that human populations are able to increase faster than
the food supply can
 Unchecked populations grow by geometric progression
 Food supplies grow by arithmetic progression
 Proposed human population do not grow unchecked because
death caused by disease, war, and famine slows population
growth
Growth of Populations
 Population: consists of all the individuals of a
species that live in a specific geographical area and
that can interbreed
Evolution by Natural Selection
 Darwin realized Malthus’s hypothesis about human
population applied to all species
 Every organism has potential to produce many
offspring during its lifetime
 In most cases, only a limited number of offspring
survive to reproduce
Evolution by Natural Selection
 Darwin connected Malthus’s ideas with his own
observations and ideas
 Individuals that have physical or behavioral
traits that better suit their environment are
more likely to survive and will reproduce
more successfully than those that do not have
such traits
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Natural Selection
Natural Selection
Evolution by Natural Selection
 In time, the number of individuals that carry
favorable characteristics that are also inherited will
increase in a population

Nature of population will change- evolution
Evolution by Natural Selection
 Proposed organisms differ from place to place
because their habitats present different challenges to
and opportunities for survival and reproduction
 Adaptation: is an inherited trait that has become
common in a population because that trait provides a
selective advantage
Publication of Darwin’s Work
 1844, Darwin wrote down his
ideas about evolution and natural
selection
 Published in 1858
 Presented with Alfred Wallace
who was coming to the same
conclusion as Darwin was about
natural selection and evolution
Darwin’s Theory
Inherited variation exists within the genes of every
population or species (the result of random
mutation and translation errors)
2. In a particular environment, some individuals of a
population or species are better suited to survive
(as a result of variation and have more offspringnatural selection)
1.
Darwin’s Theory
3. Over time, the traits that make certain individuals
of a population able to survive and reproduce tend
to spread in that population
4. There is overwhelming evidence from fossils and
many other sources that living species evolved from
organisms that are extinct
Darwin’s Ideas Updated
 Change Within Populations:
 Now know genes are responsible for inherited traits
 Certain forms of a trait become more common in a population
because more individuals in the population carry the alleles for
those forms
 Natural selection causes the frequency of certain alleles in a
population to increase or decrease over time
 Mutations and recombination of alleles that occurs during
sexual reproduction provide endless sources of new variations
of natural selection to act upon
Darwin’s Ideas Updated
 Species Formation:
 The environment differs from place to
place
 Populations of the same species living in
different locations tend to evolve in
different directions
 Reproductive isolation: condition in
which two populations of the same species
do not breed with one another because of
geographic separation, difference in
mating periods, or other barriers to
reproduction

May eventually become unable to breed
together
Darwin’s Ideas Updated
 The Tempo of Evolution:
 Gradualism: model of evolution in which gradual change
over a long period of time leads to species formation
 Suggested that successful species may stay unchanged for long
periods of time (Gould and Eldredge)
 Major environmental events in the past have caused major
evolution to occur in spurts
 Punctuated equilibrium: model of evolution, in which
periods of rapid change in species are separated by periods of
little or no change
 Evidence for both
Review
T/F Malthus and Lyell influenced Darwin in his
ideas of natural selection
2. T/F The number of individuals that carry favorable
characteristics that are also inherited will increase
in a population
3. T/F The smallest scale that evolution happens on
is the individual
1.
Answers
1. T/F Malthus and Lyell influenced Darwin in his
ideas of natural selection
2. T/F The number of individuals that carry
favorable characteristics that are also inherited will
increase in a population
3. T/F The smallest scale that evolution happens on
is the individual

Smallest scale is at the population level, individuals
don’t evolve, populations do