Transcript Evolution - Cloudfront.net

Evolution
Definition: How species change
over time.
Ex: What where humans before we evolved to become humans? Hint: Not
Monkeys….Monkeys and Humans evolved from a similar ancestor (But
scientists are still unsure of the exact answer).
Lamark’s Theory
 Lamark thought that animals could
adapt to their environments and then
pass these acquired characteristics
along to their offspring.
 For example: He thought that giraffes couldn’t reach
the leaves on tall tree, so they stretched their necks
until they got longer. Then these giraffes passed this
trait on to their offspring.
 We know that can’t be true because you only pass on
your DNA to your offspring.
 If you have surgery to make you taller this is not in
your genes and cannot be passed on to your
offspring.
Darwin
 In 1831 Charles Darwin went for a boat ride
on the H.M.S. Beagle.
 On this trip he notices many different
organisms, he began to wonder why
organisms seemed so well suited for their
environments.
 He collected fossils as well as living
specimen.
 Finally in 1859, Darwin publishes his theory
of evolution in his paper “On the Origin of
Species”
Theory of Evolution
 There is natural variation among different organisms within a species.
 This variation is cause by meiosis (crossing over and Mendel’s Laws) and
fertilization (combining new traits from two different organisms) and
mutations (changes in the sequence of DNA)
 Adaptations are variations that occur and make an organism better suited
to survive and pass on its genes
 Organisms compete with each other for survival, causing natural
selection.
 Natural selection – the organisms with the traits that are most
beneficial will survive to reproduce and pass on those traits, while the
others will die off.
 This is also know as survival of the fittest
 Over time, natural selection changes the inherited characteristics of a
population, so modern organisms look different from their ancestors
Theory of Evolution
 Taking this a step further, Darwin proposed
common descent
 That all organisms evolved from one common
ancestor
 Evidence used to support this theory of
common descent:
 Fossil Record – by looking at structures left behind by
previous organisms we can show the changes within species
and try to make links and find common ancestors
 Geographic Distribution of Living Species – many
organisms across the world are very similar, yet have
distinct differences that make them more suited for their
particular environment
 Homologous Structures – structures that serve different
functions, but are structurally similar
 Early Development – most embryos with a backbone go
through very similar stages during development and look
very similar
Artificial
Selection
 Sometimes humans interfere with
natural selection (we’ve already
talked about this because of
selective breeding)
 We breed organisms based on
traits that would normally not be
selected in nature.
 Ex: We choose cows that produce more milk, dogs that have a gentle
demeanor, crops that taste better or produce more, etc . . .
 What other examples of artificial selection can you think of?
Rates of Evolution
 Evolution is a slow process.
 Gradualism – Some scientists speculate that the
genetic changes occurring in species occurs at a
constant rate very slowly. They speculate that
evolution is a process like erosion. It causes huge
changes because tiny changes are occurring
constantly.
 Punctuated Equilibrium – Other scientists
speculate that there are long periods where
nothing happens, but occasionally big changes in
species occur. These could be because of dramatic
changes in the climate such as an ice age or due to
natural disasters.
Patterns of
Evolution
 Convergent Evolution – when
two species develop similar traits
because they play similar roles in the environment. These adaptations are
not similar because they share a common ancestor!
 EX: sugar gliders in Australia and flying squirrels in North America
 Divergent Evolution – when two species do share a
common ancestor, but change drastically because of
their different niches, or roles in the environment.
 EX: finches on the Galapagos Islands
 Phylogeny – evolutionary history of an organisms or
group of
Natural Selection Video
 During the video watch closely and answer the questions below:
 What things do you think would help a zebra survive?
 What things do you think help the lions survive?
 Is this natural or artificial selection? How do you know?
 What zebras did the lions attack?
 If I told you that lions were colorblind, what other trait do you think has
developed in the zebra population to help them survive?
Discussion
 Is there natural selection within the human population?
 If so, what traits are selected for in humans?
 Moth example:
 Before the industrial revolution which moths thrived?
 After the industrial revolution which moths thrived?
 Is this natural or artificial selection? Explain.
 Why is biodiversity important?