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Evolution – How Change Occurs . Biology I Honors – Ch. 15. Some things to keep in mind BEFORE we study evolution... the nature of SCIENCE. What is SCIENCE? A process that seeks to find natural explanations for observations of the natural world

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evolution how change occurs

Evolution – How Change Occurs

Biology I Honors – Ch. 15

some things to keep in mind before we study evolution the nature of science
Some things to keep in mind BEFORE we study evolution...thenature of SCIENCE.
  • What is SCIENCE?
    • A process that seeks to find natural explanations for observations of the natural world
    • Science cannot comment on anything that is outside the realm of the physical/natural.
      • Philosophy
      • Ethics / morality
      • Religion
    • Nor do philosophy, etc. operate in the terms of science. Religion, philosophy, etc. are valuable tools designed to help people answer MANY important (perhaps THE MOST important) questions, but NOT scientific questions.
      • Questions like
        • why is the sky blue,
        • how do bacteria cause disease,
        • How do cells become cancerous?
        • How can we kill cancer cells?...

are answerable by science…

questions like:

“What’s the meaning of life?” are NOT.

the nature of science
The nature of science
  • Science cannot comment on whether religious stories of the creation of life on Earth are true or untrue…
  • It’s just that religious stories are not SCIENTIFIC explanations because they cannot be tested scientifically and are not meant to be. They are outside the realm of our natural laws that we observe day to day.
  • Science relies on observations of the natural world and in finding natural explanations for those observations.
  • Science, like religion, philosophy, math, poetry, etc. works with a specific set of RULES. Anything that does not follow these rules may WELL be VERY important, but it cannot fall under the definition of science.
what are the rules of science
What are the rules of science?
  • Rule 1:
    • We rely on observations of the natural world to explain phenomena we see.
what are the of rules of science
What are the of rules of science?
  • Rule 2: Science is TESTABLE
    • Scientific questions must be TESTABLE and that means the you can make observations either through experimentation or some other means to test whether a hypothesis is wrong.
    • Ideas of religion, morality, philosophy CANNOT be “tested” with experiments or observations and are not meant to be.
    • For example, The whole point of religion is that it is based on faith, NOT whether a hypothesis was “accepted” or “rejected” based on “evidence”.
what are the of rules of science6
What are the of rules of science?
  • Rule 3: Science can beWRONG!
    • Scientific process is designed to correct itself
    • If a scientific idea is found to be wrong or partially wrong, the whole point of science is for evidence to be presented to fix the idea
    • If evidence arises to disprove an idea, the idea will be either modified to fit the new evidence or it will be discarded all together.
    • Generally, faith/religion cannot be wrong in the eyes of those who believe.
other things to keep in mind before we study evolution theory vs hypothesis
Other Things to Keep in Mind before we study Evolution... Theory vs. Hypothesis
  • It’s called the THEORY of Evolution – what does this mean??
what s a hypothesis
What’s a hypothesis?
  • A possible explanation for an observation
    • It’s NOT been tested a lot
    • It’s NOT been supported by a lot of evidence.
    • Often in everyday usage, people say “I have a theory about…” when what they really mean is “hypothesis”.
what is a theory
What is a Theory?
  • It’s an idea that
    • Explains a lot of observable phenomena
    • Has been supported by a large body of evidence
    • Has been studied by many people and tested a LOT.
    • In science it explains something about how things happen in the natural world
      • Fact: An apple falls from a tree
      • Theory: Newton’s theory of gravitation explains WHY the apple falls from the tree.
so what exactly is evolution
So, what exactly IS evolution?
  • Evolution = the kinds of organisms on Earth have changed over time
    • This is observable. It is nothypothesis or theory, but fact.
    • Best evidence is fossil record, which we will talk about later…
  • Natural Selection is the theory part…
    • This is the WAY (mechanism) by which evolution occurs
    • Fact: Fossil record shows that over time life on Earth has changed
    • Theory: Natural selection explains how life on Earth has changed.
note that neither evolution nor natural selection is a
Note that neither evolution nor natural selection is a…
  • Guess
  • Opinion
  • Hypothesis
  • The vast majority of scientists agree that the evidence points to natural selection as the mechanism that causes evolution to happen.
    • This is well supported by lots of research, over long periods of time, by lots of people ---- that is, it’s a THEORY.
    • In science a theory is a BIG DEAL
      • Other theories:
        • Cell theory
        • Newton’s theory of gravitation
        • Copernicus – Earth moves around the sun
where did the idea of evolution come from
Where did the idea of evolution come from?
  • Not from Charles Darwin
  • The idea of Evolution has been around for a very long time
    • Aristotle (Greeks)
  • Darwin is just the one who told us the MECHANISM by which evolution could occur
ideas before darwin
Ideas before Darwin
  • Lamarck
    • Said organisms evolved by passing on traits acquired during their lifetime
    • Wrong
    • Example:
      • Said giraffes stretched their necks to reach leaves
      • Passed on their stretched necks to their offspring
        • “Inheritance of Acquired Characteristics”
who is charles darwin
Who is Charles Darwin?
  • British
  • Born 1809
  • Tried many careers
    • Minister
    • Doctor
  • Became ship’s naturalist aboard the HMS Beagle
    • 1831-1836
    • Focus of ship was to map coast of S. America and collect specimens of life forms there
hms beagle
HMS Beagle
  • It was Darwin’s job to hike the coast of S. America wherever the Beagle stopped.
  • He made notes describing land forms, etc.
  • He collected LOTS of specimens
    • Living and fossils
    • Many never before seen by Europeans
voyage of the hms beagle
Voyage of the HMS Beagle
  • Stopped in Galapagos Islands
    • 500 miles off coast of Ecuador
galapagos islands18
Galapagos Islands
  • Of particular interest to Darwin were the plants and animals he found on the Galapagos Islands
  • He noticed that the forms of plants and animals on these islands were often similar to those on mainland S. America, but modified to be adapted to the various different island habitats on which they lived.
    • Why are they similar to S. American organisms??
    • Why not more similar to other island species that live in similar habitats?
darwin found birds





Darwin found… birds

Collected many different birds on the Galapagos Islands.



Thought he had found many, very differentkinds of birds…



but what he found was many different kinds of finches
But what he found was many different kinds of finches

Darwin was amazed to find out:

All 13 species of birds were finches…

But there is only one species of finch on the mainland!

Small Ground Finch


Large Ground Finch

Did one species of finches becomemany differentspecies? If so,


Woodpecker Finch

Warbler Finch

example darwin s finches
Example – Darwin’s Finches
  • Darwin found several different species of finch on the Galapagos Islands
  • Each species was specifically adapted to feed in the particular habitat in which it lived
  • Each was at least somewhat similar to the others AND to a finch commonly found on the S. American mainland
  • Why?
example darwin s finches22
Example: Darwin’s Finches
  • Darwin suggested that the solution to this puzzle that made the most sense was that the original mainland ancestor colonized one of the islands many years ago
  • It’s descendents slowly became adapted to the various food sources available on the many different island habitats
darwin s book
Darwin’s Book
  • After many years of pouring over his notes and specimens, Darwin finally published his ideas in a book
  • On the Origin of Species
  • 1859
  • His book was controversial upon its release, as it remains within some groups today.
  • Despite the so-called controversy, Darwin’s ideas are the centerpiece upon which all of biology is based.
    • His ideas are not controversial among biologists.
why was darwin so hated by some
Why was Darwin so hated by some?
  • Some people felt that Darwin’s ideas challenged their religious beliefs
    • Some felt that Darwin’s ideas implied there was no God
    • Some felt that Darwin’s ideas meant that there was no moral imperative for people to “do good”
  • In reality, Darwin made no judgments about God or religion in his work and did not see why his work had to be at odds with religion.
what exactly did darwin say
What exactly did Darwin say?
  • Organisms overreproduce
    • make more babies that the environment can possibly support.
what exactly did darwin say28
What exactly did Darwin say?
  • Leads to competition for resources
what exactly did darwin say29
What exactly did Darwin say?
  • Not all organisms are equal in the competition because VARIATION exists among offspring.
  • Not all organisms are identical
what exactly did darwin say30
What exactly did Darwin say?
  • This variation must be INHERITABLE to be important in natural selection because you must be able to pass it on to offspring.
what exactly did darwin say31
What exactly did Darwin say?
  • Organisms that are better suited to their environment will outcompete those that are less well suited.
  • Over lots of time, the less well-suited organisms will “lose out” to the better suited ones.
what exactly did darwin say32
What exactly did Darwin say?
  • The “winning competitors” will survive and pass on their traits to their offspring more often than the “losing competitors”
what exactly did darwin say33
What exactly did Darwin say?
  • Over lots of time, the species will come to possess the “good” characteristics possessed by the “winning competitor”.
other facts that are important to evolutionary theory
Other facts that are important to evolutionary theory…
  • The Earth is REALLY, REALLY OLD.
    • 4.6 billion years old
    • The Earth HAS to be old IF evolutionary change by natural selection is to work
    • It takes a LONG time.
remember what natural selection says
Remember What Natural Selection Says…
  • Over lots of time, the less well-suited organisms will “lose out” to the better suited ones.
  • Over lots of time, the species will come to possess the “good” characteristics possessed by the “winning competitor”.
  • Over lots and LOTS of time, many such small “improvements” may accumulate and alter the species in such a major way that a new species is created.
    • SPECIATION – creation of a new species
darwin and artificial selection
Darwin and Artificial Selection
  • Artificial Selection
    • Choosing organisms with certain traits and breeding them
      • In this case the human is the “selector” instead of the environment, but the principle of section is the same.
    • Can lead to organisms that look VERY different from the originals in just a relatively few generations
darwin and artificial selection38
Darwin and Artificial Selection
  • Darwin noticed the effects of artificial selection on plants and animals and argued that…
    • If humans could have such a dramatic effect on some species of plant/animal in such a short period of time, imagine what nature could do over MILLIONS of years of time.
examples of natural selection the peppered moths
Examples of Natural Selection – The Peppered Moths
  • Peppered moths typically rest on tree trunks
examples of natural selection the peppered moths40
Examples of Natural Selection – The Peppered Moths
  • At the beginning of the 19th century (before the industrial revolution), most of the tree trunks in England were light in color
  • So were most of the Peppered Moths
  • Camouflage – hard for predators to find them.
examples of natural selection the peppered moths41
Examples of Natural Selection – The Peppered Moths
  • However, a few darker Peppered Moths would also appear occasionally in the population.
  • These did not blend so well on the light trees
  • No camo = LUNCH for birdies!
examples of natural selection the peppered moths43
Examples of Natural Selection – The Peppered Moths
  • Industrial Revolution begins – pollutants (soot) in the air from smokestacks begin to cover surfaces, including tree trunks.
  • This makes the tree trunks DARKER.
  • Suddenly, the light moth is no longer wearing “camo”
examples of natural selection the peppered moths44
Examples of Natural Selection – The Peppered Moths
  • Does the dark moth being more common mean that a new species arose?
    • NO
      • The dark moth increased in number - simply became more common
      • The light moth decreased in number
    • This is called microevolution
      • Evolution on a small scale; tiny changes in a population of organisms
    • Yes, only a small change
      • But remember – natural selection says that many small changes may accumulate over many years which may eventually lead to a new species being created.
examples of natural selection the peppered moths45
Examples of Natural Selection – The Peppered Moths
  • Over just a few generations, the dark moth became the prevailing type found in England.
  • Does this mean the light moths no longer existed?
  • What might happen if the pollution were cleaned up??
what is the source for the variation we see in the moths or any other organisms
What is the source for the variation we see in the moths (or any other organisms)?
  • Remember that variation does NOT occur because an organism “wants” or “needs” to “evolve”.
  • Variation just happens (RANDOM) – WHY?
    • Because MUTATION just happens
    • Because crazy new combinations of genes just happen when organisms sexually reproduce.
      • Sexual Recombination
the spread of genes among organisms or the decline of genes among organisms
The Spread of Genes among Organisms (or the decline of genes among organisms…)
  • Scientists do NOT study individuals when they study evolutionary change.
    • A mutation occurring in ONE individual does not mean that an evolutionary change has occurred.
    • A mutation in ONE individual does not mean a new species has occurred
  • Scientists study POPULATIONS
    • Collection of individuals of the same species in a given area. The members of a population can breed with each other.
some terms
Some Terms…
  • Gene Pool
    • All the genes within a population of organisms
  • Relative Frequency
    • The number of times one allele appears in the gene pool as compared to some other allele
      • Example:
        • White allele originally appeared 90% of the time in the moth population.
        • Black allele only 10% of the time.
    • If the relative frequency of the alleles in a population change over time, then evolutionary change is occurring
what constitutes an evolutionary change
What constitutes an Evolutionary Change?
  • Evolutionary change involves change in the relative frequencies of certain alleles in the gene pool.
    • How often certain genes show up in the gene pool.
species and evolutionary change
Species and Evolutionary Change
  • What exactly is a species?
    • Species – A group of similar-looking, though not identical organisms that breed with one another and produce fertile offspring in the natural environment (not the zoo).
species and evolutionary change51
Species and Evolutionary Change
  • Because members of a species (population) can breed with each other, they share a common gene pool.
  • Because of that, when a genetic change occurs in an individual, it can spread through the population as that individual and its offspring mate with other individuals.
  • IF that gene INCREASES FITNESS, it will eventually be found in MANY individuals in the population (species?)
  • When new species evolve from old ones
how does speciation occur
How Does Speciation Occur
  • members of a population must get separated
  • If the members are separated such that they cannot interbreed, they are in reproductive isolation
  • If you have two distinct populations that can’t interbreed (can’t share genes) then natural selection can work differently on each group
    • Perhaps their environments are different, etc.
  • Because their gene pools are separate, adaptations that appear in one group are NOT passed onto the other.
how can a population get separated reproductive isolation
How can a population get separated? (reproductive isolation)
  • Geographic Barrier
  • Differences in behaviors may arise, fertile periods, etc.
  • Once separation occurs, natural selection usually increases differences between pops.
  • Pops. become adapted to different environments, separate gene pools become more dissimilar
  • If the populations remain separated for a long time, their gene pools beomce so different that their reproductive isolation becomes PERMANENT.
  • They are now not just separate populations, but separate species.
adaptive radiation
Adaptive Radiation
  • Once species gives rise to many species
convergent evolution
Convergent Evolution
  • Organisms that are not closely related share similar physical adaptations because of the environment/niche they occupy
analogous structures
Analogous Structures
  • Structures that are similar in appearance and function, but do NOT share a common origin
  • Bird wing and butterfly wing
  • Says evolutionary change occurs slowly/gradually
  • Darwin’s original idea
modifications to darwin s idea of gradualism
Modifications to Darwin’s idea of Gradualism
  • Environmental change can cause evolution to go faster
  • More evolutionary change after a mass extinction
    • Lots of habitat, niches to fill
  • Punctuated equilibrium
    • A more modern modification of Darwin’s original idea
    • Long stable periods interrupted by brief periods of rapid change