EVOLUTION BY NATURAL SELECTION

EVOLUTION BY

NATURAL SELECTION

Descent with Modification

Evolution by Natural Selection

• Biodiversity – the measure of the variety of

different species in an environment.

• Charles Darwin proposed the theory of

evolution by natural selection or descent
with modification.

• Evolution – populations changing over time

or descent with modification

• This definition encompasses small-scale

evolution: changes in gene frequency in a
population from one generation to the next
and large-scale evolution: the descent of
different species from a common ancestor over
many generations.

• False Evolution Ideas:

• Acquired Characteristics - gaining traits in an

individual's lifetime and passing it on to offspring

• Use and Disuse - keep traits that are used and

lose traits that aren’t used

www.biography.com

evolution.berkeley.edu/

Multiple Choice

Who is the father of evolution?

• Charles Darwin
• Galileo Galilei
• Albert Einstein
• Isaac Newton

Evolution by Natural Selection

• Natural Selection – is the diversity and changing of

life forms over many generations. Natural selection
leads to a diversity of organisms whose body
structure and behavior is best suited to survive and
reproduce in a specific environment.

• Natural selection is simply the logical result of four

features of living systems:

• variation - individuals in a population vary from one

another (from mutations and genetic recombination)

• inheritance - parents pass on their traits to their offspring

genetically

• selection - some individuals reproduce more than others
• time - successful variations accumulate over many

generations

• Sexual reproduction increases variation and helps

increase natural selection. Asexual reproduction is
one of the least effective mechanisms for natural
selection.

evolution.berkeley.edu/

Multiple Choice

What process demonstrates individuals best suited for their environment survive and reproduce?

• artificial selection
• natural selection
• random selection
• unnatural selection

Multiple Choice

Which factors must be present for natural selection to occur?

• Mutation, migration, and genetic drift
• Variation, heredity, and differential reproductive success
• Competition, cooperation, and symbiosis
• Random chance, luck, and fate

Multiple Choice

What increases genetic variation and natural selection?

• Asexual reproduction

• Decrease in population size
• Sexual reproduction

• Genetic drift

Example of Natural Selection

1. In a population of giraffes, there will
be variation of traits, some having
shorter or longer necks and legs.

2. During periods of high competition,
giraffes with long necks and
legs can reach the leaves of the
upper branches of acacia trees to
eat, so they will be more likely to
survive and reproduce. The shorter
giraffes would perish of hunger if they
could not reach as many leaves.

3. Generation after generation, the
population will have more and more
giraffes with long legs and necks.

Peppered Moth Example

Peppered moths (Biston betularia) exist in two distinct polymorphic
forms – a light colouration and a darker melanic variant

•In an unpolluted environment, the trees are covered by a
pale-coloured lichen, which provides camouflage for the lighter
moth

•In a polluted environment, sulphur dioxide kills the lichen while
soot blackens the bark, providing camouflage for the dark moth

The frequency of the two different
forms of peppered moth is
dependent on the environment and
evolves as conditions change

●Before the industrial revolution,
the environment was largely
unpolluted and the lighter moth
had a survival advantage

●Following the industrial
revolution, the environment
became heavily polluted,
conferring a survival advantage
to the darker moth

●Recent environmental policies
in Europe are reducing pollution
levels, altering the frequency of
the two populations once
again

Survival of the Fittest

• Survival of the Fittest – The term fitness in an

evolutionary sense is a measure of an
individual’s ability to survive and reproduce
more offspring that can in turn survive and to
reproduce. (Does not necessarily mean
strongest or fastest, it could be an organism
with the best camouflage or best defense
mechanism.)

• Examples: Caring for your offspring (top left),

and producing thousands of young — many
of whom won't survive (top right), and
sporting fancy feathers that attract females
(bottom) are a burden to the health and
survival of the parent. These strategies do,
however, increase fitness because they help
the parents get more of their offspring into
the next generation.

evolution.berkeley.edu/

Sexual selection - is when
one partner chooses the
other for mating due to
characteristics that they
like. Example, a peahen
may choose a peacock
based on the size and
coloration of his feathers.
The competition is
between males of that
species.

Multiple Choice

What do you call a measure of the ability of an organism to survive and reproduce fertile offspring?

• adaptation
• survival
• reproduction
• fitness

Evolution by Natural Selection

• Conditions for Evolution by Natural Selection to

occur in a population:

• Must have genetic variation in a population from

mutations or genetic recombination.

• Overproduction is when more individuals are born in

a population than can survive.

• Limited resources causing competition within the

population (struggle for survival).

• Changing environment selects for specific genetic

phenotypes.

• Adaptations: trait that helps an organism survive

and reproduce fertile offspring within a specific
environment.

• Favorable adaptations survive, reproduce and

pass on the genes/alleles.

• The accumulation and change in favored alleles

leads to evolution of a population of species.

• Genes mutate 🡪 Individuals survive and

reproduce 🡪 Populations evolve

http://missevrardbio1.blogspot.com/

Multiple Select

What factors must be present for evolution by natural selection to occur?

• Genetic Variation

• Population Overproduction

• Competition of Limited Resources

• Environment Selects for Phenotypes

• Acquired Characteristics Passed to Offspring

Multiple Choice

What is an adaptation?

• An adaptation is a trait or characteristic that helps an organism survive and reproduce in its environment.
• An adaptation is a change in an organism's DNA.
• An adaptation is a behavior that an organism learns.
• An adaptation is a physical feature that an organism develops over time.

Adaptive Radiation

• Adaptive Radiation - an event in

which a lineage rapidly diversifies,
with the newly formed lineages
evolving different adaptations.

http://evolution.berkeley.edu/

www.britannica.com

Multiple Choice

What is adaptive radiation?

• The process by which a single species evolves into diverse forms that occupy different ecological niches.
• The process by which multiple species evolve into a single form that occupies a specific ecological niche.
• The process by which a single species evolves into diverse forms that occupy the same ecological niche.
• The process by which a single species evolves into similar forms that occupy the same ecological niche.

Darwin’s Galapagos Finches

There are now at least 13 species of finches on the Galapagos Islands,
each filling a different niche on different islands. All of them evolved
from one ancestral species, which colonized the islands only a few
million years ago. This process, whereby species evolve rapidly to
exploit empty ecospace, is known as adaptive radiation.

The ecological niches exert the selection pressures that push the
populations in various directions. On various islands, finch species have
become adapted for different diets: seeds, insects, flowers, the blood
of seabirds, and leaves. The ancestral finch was a ground-dwelling,
seed-eating finch. After the burst of speciation in the Galapagos, a
total of 14 species would exist: three species of ground-dwelling
seed-eaters; three others living on cactuses and eating seeds; one
living in trees and eating seeds; and 7 species of tree-dwelling
insect-eaters.

Geographic Isolation

• Geographic Isolation – Sometimes

organisms of the same species become
physically separated. The evolution of
separate species is largely due to genetic
drift (chance) or random mutations. After
a long period of time even if the two
groups were to meet back up the
organisms may refuse to mate. At this point
they would be considered separate
species. Or they could be so genetically
different that they can no longer produce
fertile offspring and would now be two new
species.

• Because of geographic isolation the

variations in traits would decrease and the
possibilities of adaptations is limited to
certain variations.

http://www.bbc.co.uk/

Multiple Choice

Why do species evolve when they are geographically isolated for years?

• Genetic differences decrease between populations.
• Geographical isolation prevents species from evolving.
• Geographical isolation causes species to become extinct.
• Genetic differences accumulate between populations.

Genetic Bottleneck or Drift

A severe genetic bottleneck occurred in northern elephant seals. Other animals known to
be affected by genetic bottlenecks include the cheetah and both ancient and modern
human populations.

Multiple Choice

What is genetic bottlenecking?

• A process by which new genetic variations are introduced into a population.
• A population undergoing a drastic reduction in size resulting in a loss of genetic diversity.
• A population undergoing a drastic increase in size resulting in a loss of genetic diversity.
• A phenomenon where genetic mutations occur at a higher rate than normal.

Multiple Choice

What is genetic drift?

• Change in allele frequency due to natural selection
• Intentional change in allele frequency in a population
• Gradual change in allele frequency in a population
• Random change in allele frequency in a population

How did early life on Earth change?

• Early conditions of Earth were harsh with no oxygen in

the atmosphere. The simplest way to gain nutrients would
be to eat them. These cells were very simple with no
nucleus and small in size. Life started as unicellular,
anaerobic, heterotrophic, prokaryotes.

• Then some of the population of prokaryotes developed

the ability to use the sun’s light to make energy in the
form of photosynthesis and become autotrophic. As
these unicellular, anaerobic, autotrophicprokaryotes
went through photosynthesis they would be producing
oxygen as a byproduct.

• Oxygen began to fill the atmosphere and as it did some

of the prokaryotes formed the ability to more efficiently
produce ATP and are known as aerobicprokaryotes.

• Over time, new organelles that would help the efficiency

of various biological processes within the organisms
would develop forming a new population of eukaryotic
organisms.

• Later multicellular organisms would evolve to form more

complex organisms.

Animals
Evolve

Multiple Choice

What characteristics did the earliest life forms on earth possess?

• unicellular, anaerobic, heterotrophic, prokaryotic

• multicellular, anaerobic, autotrophic, prokaryotic

• unicellular, aerobic, heterotrophic, eukaryotic

• multicellular, aerobic, autotrophic, eukaryotic