Transcript Evolution for Beginners

Evolution for
Beginners
Let’s Start From the Basics
• Some organisms adapt to their conditions,
whether it be physical or a behavior.
Differences Among Organisms
• Organisms that share the same
characteristics are considered a species.
ex. Homo sapiens (humans)
In order for an organism to be considered a
species (scientifically), they must be able to
reproduce offspring that can also reproduce.
Do Organisms Change Over
Time?
Think:
Have all species that are found on Earth
today always existed?
(keep in mind that Earth is 4.6 billion years
old)
What is evolution?
A basic definition of evolution…
The process by which populations
gradually change over time….
So what does the definition mean?
• Evolution is a change in the number of
times specific genes that code for specific
characteristics occur within an interbreeding
population
• Individuals don’t evolve, populations do
• There is no implied “improvement” in
evolution
Genetic Variation and
Evolution
• Evolution: changes through time
1. Species accumulate difference
2. Descendants differ from their ancestors
3. New species arise from existing ones
Evidence of Change
• We know that fossils are the remains of
once living organisms (animals or plants).
• Scientists have organized these remains and
labeled it as the fossil record. This
organizes organisms based on their
similarities and or age groups.
A Brief History of Evolution
Charles Darwin was born on
February 12, 1809 in Shrewsbury,
England.
From 1831 to 1836 Darwin served as
naturalist aboard the H.M.S. Beagle on
a British science expedition around the
world.
He observed much variation in related
or similar species of plants and animals
that were geographically isolated from
each other.
These observations were the basis for
his ideas.
Galapagos Iguanas
Giant Tortoises
The giant tortoise is a unique animal
found only in the Galápagos Islands.
There are only about 200 tortoises
remaining on these islands.
Darwin’s Finches
• Most studied.
• Each island had its
own distinct species.
• Beaks differed in size
and shape.
On the Origin of Species by Means
of Natural Selection.
• Published in 1859
• Describes Darwin’s
observations and
• Evidence he
collected
• To formulate the
Theory of Evolution
http://spencer.lib.ku.edu/exhibits/darwin/or
A Brief History of Evolution
Darwin presumed that populations of individuals
changed over time, and, in 1844, he developed
the concept of the driving force for evolution. It
wasn’t until many years later that he published
his idea.
“I have called this principle, by which
each slight variation, if useful, is
preserved, by the term Natural Selection.”
—Charles Darwin from "The Origin of Species“,
1859
Natural selection: mechanism
of evolutionary change
Natural selection:
proposed by Darwin;
the process by which
organisms that are
better adapted to their
environment survive
and reproduce more
successfully than less
well adapted
organisms do.
• individuals have specific
inherited characteristics
• they produce more surviving
offspring
• the population includes more
individuals with these
specific characteristics
• the population evolves and is
better adapted to its present
environment
Natural Selection
Observation 1: Organisms generally
have more offspring than can survive to
adulthood.
Observation 2: Offspring are not
identical. There is variation in their
appearance, size, and other
characteristics.
Natural Selection
Inference: Those organisms that
are better adapted to their
environment have a greater
likelihood of surviving to adulthood
and passing these characteristics
on to their offspring.
Survival of the “fittest.”
Survival of the
“fittest.”
Darwin’s
theory for
how long
necks
evolved in
giraffes
Sources of variation
Selection
• Natural selection: environmental conditions
determine which individuals in a population
produce the most offspring
• 3 conditions for natural selection to occur
– Variation must exist among individuals in a population
– Variation among individuals must result in differences
in the number of offspring surviving
– Variation must be genetically inherited
Forming a New Species
• Drastic changes can form a new species
Ex. Weather changes, separation from the
population
Speciation is the formation of the a new
population.