Transcript Theory of Evolution

Objectives:
1. Explain what a theory is and a law and explain the
difference between them.
2. Identify Darwin’s observations and their role to
conclude that species evolve.
3. Identify ideas that Darwin evolved from his Voyage
on the HMS Beagle
4. Explain natural selection.
 Guess or hunch
 Science: set of statements that explain the natural world.
 Science is controlled by experiments, data collection, and
theories to explain what has been observed.
Definition:
A scientific theory summarizes a hypothesis or group of
hypotheses that have been supported with repeated testing. A
theory is valid as long as there is no evidence to dispute it.
Therefore, theories can be disproven. Basically, if evidence
accumulates to support a hypothesis, then the hypothesis can
become accepted as a good explanation of a phenomenon. One
definition of a theory is to say it's an accepted hypothesis
(about.com)
Law
A law generalizes a body of observations. At the time it is made, no
exceptions have been found to a law. Scientific laws explain things, but
they do not describe them. One way to tell a law and a theory apart is to
ask if the description gives you a means to explain 'why'.
 Example: Consider Newton's Law of Gravity. Newton could use this law
to predict the behavior of a dropped object, but he couldn't explain why
it
(about.com)
 A change in the genetic characteristics of a population
over time
 Well-supported based on a variety of evidence
including fossil records, diversity of organisms, and
similarity across species of anatomy and development.
 Refers to common descent of organisms from shared
ancestors.
Roman Philosopher, (Lucretius)lived 1,900 years before theory of
evolution existed, believed organisms could not continue their species
unless they were able to survive and produce offspring.
- this was not even looked at until 18th and 19th century
2. Used to be that everyone believed that species were unchanging.
3. 1809: Jean Baptise Lamarck proposed a process in which evolution
happened.
a. Use and disuse of physical features: increase in size if used
and decrease in size if not used.
b. Thought linked to environmental conditions
1.
Charles Darwin
a. Studied medicine but did not like surgery.
b. Father sent him to Cambridge Univ. To study ministry where he
completed degree in theology.
4. Charles Darwin, went on a 5 year voyage on the ship HMS Beagle. (See
route)
a. Found fossils in South America of armadillos. They were
closely related to the armadillos but not exactly the same
as the armadillos in that area.
b. Galapagos Islands: found plants and animals that
were found on the nearby coast of South America.
- explanation that the ancestors on the Galapagos
latter changed. (descent with modification)
 The longest part of his voyage: 5 weeks
 He collected specimens of finches from 3
islands
 All in all he collected 9 distinct species all similar to each other except their
bills
1. fruit eater
2. cactus eater
3. large bills crush seeds
4. narrow bill eats insects
5. sharp beak feeds on
blood of sea birds
 One ancestral finch evolved to
adapt to different food sources
We've defined evolution as descent with modification from a common ancestor, but
exactly what has been modified? Evolution only occurs when there is a change in
gene frequency within a population over time. These genetic differences are heritable
and can be passed on to the next generation — which is what really matters in
evolution: long term change.
Compare these two examples of change in beetle populations. Which one is an example of
evolution
1. Beetles on a diet
Imagine a year or two of drought in which there are
few plants that these beetles can eat.
All the beetles have the same chances of survival and reproduction, but
because of food restrictions, the beetles in the population are a little smaller
than the preceding generation of beetles.
2. Beetles of a different color
Most of the beetles in the population (say 90%) have the genes for
bright green coloration and a few of them (10%) have a gene that makes
them more brown.
Some number of generations later, things have changed: brown
beetles are more common than they used to be and make up 70% of the population.
http://evolution.berkeley.edu/evolibrary/article/evo_15
Which example illustrates descent with modification — a change in gene
frequency over time?
The difference in weight in example 1 came about because of environmental
influences — the low food supply — not because of a change in the frequency
of genes. Therefore, example 1 is not evolution. Because the small body size in
this population was not genetically determined, this generation of small-bodied
beetles will produce beetles that will grow to normal size if they have a normal
food supply.
The changing color in example 2 is definitely evolution: these two generations
of the same population are genetically different. But how did it happen?
Thomas Malthus: wrote an essay in 1798 how
human populations increase faster than food
supply.
2. He said that humans should cover the earth in a
very short time however this is not what
happens because of death due to disease, war,
and famine. This slows population growth.
3. Population definition: all individuals of a
species that live together in one place at one
time.
1.
1. Darwin took Malthus’s information in his essay and said that this
could apply to all species. All species can reproduce many
offspring in its lifetime however, only a few offspring survive.
2. Incorporating Malthus’s information and what he found on his
voyage he came up with this
a. Individuals that have physical or behavioral traits that better
suit their environment are more likely to survive and
reproduce than those that do not have such traits.
3. Darwin suggested that species that survive long enough to
reproduce pass on favorable traits to their offspring, in time these
favorable characteristics will increase in population and the
population will gradually change over time.
4. NATURAL SELECTION: process by which populations change in
response to their environment.
Natural selection
Natural selection is one of the basic mechanisms of evolution, along with
mutation, migration, and genetic drift.
Darwin's grand idea of evolution by natural selection is relatively simple
but often misunderstood. To find out how it works, imagine a population of
beetles:
1.There is variation in traits.
For example, some beetles are green and some are brown.
2.There is differential reproduction.
Since the environment can't support unlimited population growth, not all individuals
get to reproduce to their full potential. In this example, green beetles tend to get eaten
by birds and survive to reproduce less often than brown beetles do.
3.There is heredity.
The surviving brown beetles have brown baby beetles because this trait has a genetic
basis.
4.End result:
The more advantageous trait, brown coloration, which allows the beetle to have more
offspring, becomes more common in the population. If this process continues,
eventually, all individuals in the population will be brown.
University of California Museum of Paleontology's Understanding Evolution
(http://evolution.berkeley.edu).
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Darwin suggested that organisms differ from place to place because
habitats are different. This presents both challenges and
opportunities survival reproduction.
ADAPTATION: Changing of a species that results in betterment for
survival in their environment.
He also determined that organisms closely resembled species in a
nearby geographic region than those living in similar yet widely
separated parts of the world
Conclusion: species evolved from a species that previously lived
there or migrated from nearby areas.
Darwin published his findings in 1859. Book was called
“On the Origin of Species by Means of Natural Selection”
 Earth changed slowly over many years
 Darwin found extinct armadillo fossils that closely
resembled – living armadillos
In other words: Natural Selection - Populations change
in response to their environment
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All species have genetic variation
The environment presents many different challenges to an
individual’s ability to reproduce.
Organisms tend to produce more offspring than their environment
can support; thus, individuals of a species often compete with one
another to survive.
Individuals within a population that are better able to cope with the
challenges of their environment tend to leave more offspring than
those less suited to the environment.
The traits of the individuals best suited to a particular environment
tend to increase in a population over time.
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Scientists know that genes are responsible for inherited traits.
Certain traits become more common in a population because more
individuals in the population carry the alleles for those traits.
In other words, natural selection causes the frequency of certain
alleles in a population to increase or decrease over time.
Populations of the same species living in different locations tend to
evolve differently
Extinct: May have species that are better suited replace the ones
that become extinct (natural disaster, climate changes etc..)
 Populations of the same species living in different locations tend to
evolve in different directions.
 Isolation: two populations of the same species cannot breed with one
another.
 In other words. 2 species were the same but as they evolved through
time they have become so different that biologists consider them 2
different species.
1. Variation exists within the genes of every population or
species (resulting from random mutations).
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 offspring
(Natural selection).
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 clear proof from fossils and many other sources
that living species evolved from organisms that are extinct.