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Mr. Tsigaridis
EVOLUTION AND THE HISTORY
OF LIFE
PART 2
How Does Evolution Occur
 Charles Darwin
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Darwin’s Excellent Adventure
Darwin’s Finches
Darwin Does Some Thinking
Darwin Learned from Farmers and Animal and Plant
Breeders
Darwin Learned from Geologists
Darwin Learned from the Work of Thomas Malthaus
Natural Selection
More Evidence of Evolution (DNA Mutation)
Darwin’s Excellent Adventure
 HMS Beagle – Galapagos Island Travels
 Galapagos Islands are part of the country of
Ecuador though the islands are about 1,000
kilometers west of the continent of South
America in the Pacific Ocean. There are 19
volcanic islands with a land area of 8,000 km2
in an area of the Pacific Ocean over 60,000
About Darwin
km2
http://www.aboutdarwin.com/timeline/time_01.html
Darwin’s Finches
Diversity
 Darwin saw finches that were very different
from each other as he traveled to the various
islands of the Galapagos.
 Because of their physiological differences
(beak shapes), the finches had very different
diets
The diversity of life…
Although there is unity in life there is also a
great deal of diversity!
Estimates of Diversity:
~1.7 million cataloged species
50,000 vertebrates
260,000 species of plants
750,000 species of insects
Total diversity  5-30 million species !
Darwin Does Some Thinking
 Darwin wonders how did the finches become
so different. He thought maybe there was a
storm that separated the original population
resulting in geographic isolation (one of the
ways that speciation can occur)
Darwin Learned from Farmers and
Animal and Plant Breeders
 Darwin was very familiar with artificial
selection or better known as selective
breeding.
 Certain traits are determined by the breeder
to be favorable. If only those organisms with
the favorable traits are breed then the trait
will occur more often in the population. By
isolated certain individuals the differences
can grow.
All from an ancestral dog
Darwin Learned from Geologists
 Darwin learned from Charles Lyell that the Earth was
formed over a long period of time by natural process.
 This idea of geologic time (really really long time
ago) helped Darwin to more seriously consider
natural processes for changing populations.
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Darwin Learned from Thomas
Thomas
Malthus was an economist.
Malthus
 Malthus reasoned that humans have the potential to
reproduce beyond the capacity of their food supply.
 Malthus recognized that there are some limitations
to human population growth:
 War (for animals it is predation-predators)
 Disease
 Starvation
Competition
 Because there are some limitations to growth,
Darwin thought that those survivors must be
better equipped (adapted) to their environment
allowing them to out-compete other individuals.
 The offspring of the successful competitors have
the same traits so are also more likely to survive
in the same kind of environment.
Natural Selection
Darwin theorized that evolution occurs through a process
he called natural selection
1. Overproduction – Each species produces more
offspring that will naturally survive.
2. Genetic Variation – individuals will be slightly
different from one another.
3. Survival Struggle – competition for resources
Abiotic and Biotic factors
4. Successful Reproduction – fitness
(Survival of the fittest)
More Evidence of Evolution
 Darwin did not know what the mechanism
was for how parents passed their traits to
their offspring.
 Gregory Mendel (1822-1884) the Catholic
monk studied traits in sweet peas.
 With Mendel's work and biochemistry we
now know that the mechanism is meiosis
involving DNA that is subject to mutation.
Mutation
 Changes to the heredity material- DNA,
deoxyribonucleic acid – result in a changed
genotype.
 Some changes that occur are not observed
because the change did not significantly
affect a function. Changes that affect
function result in a different phenotype (what
things look or function like).
Types of Mutation
 Changes can occur by
 single nucleotide substitutions
 Insertions or deletions of longer sequences of
nucleotides (the components that make up
deoxyribonucleic acid
 Chromosome alterations – which can be seen
with a microscope.
SOME PHRASES ABOUT
EVOLUTION
Asking and Answering “How?”
and “Why?”
 How and why questions are usually
answered using a hypothetical-deductive
(H-D) approach.
 hypothesize
 predict
 test! - experiments (field + lab)
Hypothesis vs. Theory
“Evolution is just a theory”
Scientific theories are factual
statements about Nature.
Good theories are logically
supported
and are demonstrated by the
results from multiple tests.
“Evolution is about the
Origins of Life”
The Theory of Evolution mostly
describes how change occurred
after complex life arose.
"Nature red in tooth and
claw"
Evolution says nothing about
which traits will evolve;
only that they will change.
"Survival of the Fittest"
Cultural and ethical decisions of who is
“fittest” and should survive are not Nature’s
Laws. The term is used in business but with
a different definition of fittest
This is different from…..when fitness
involves reproduction and those
organisms that reproduce have
demonstrated fitness.