Download Theories: Theory of Evolution

Darwin’s
Theory of
Evolution
Darwin’s Theory of Evolution
When Darwin set out to explore the
Galapagos Islands, the average person
believed the world was 6,000 years old.
Everyone, including Darwin, believed that
plants and animals were unchanging,
meaning they did not change and would
not change.
Darwin’s Theory of Evolution
Darwin’s Goals: (Five year expedition)
1) To discover, survey, and map the coast of
South America.
2) Collect various rocks, fossils, plants, and
animals.
Darwin’s Theory of Evolution
During his journey, Darwin also began reading
Charles Lyell’s Principles of Geology, which made
arguments that the earth was millions of years
old.
Remember, at the time of his expedition, it was
believed that the world was only 6000 years
old…
How would these arguments influence Darwin’s
work?
Darwin’s Theory of Evolution
Well, it provided answers for…

Marine fossils found in the Andes Mountains.

Giant fossil versions of smaller living animals.
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Changes in rock elevation due to earthquakes.
The Galapagos Islands
Darwin’s Theory of Evolution
At first, Darwin was disappointed with the
bareness of the islands.
However, he quickly discovered something
unique about his collection of plants and
animals.
They were different, but the same…
Darwin’s Theory of Evolution
Darwin then realized that each island had its
own variety of the same animals!
There were finches, mockingbirds, and other
animals on all the islands.
However, each grouping of finches,
mockingbirds, etc. were unique in some way.
Darwin’s Finches and the Galapagos
Darwin noted
the different
species of
giant tortoises
on the different
islands of the
Galapagos.
Darwin’s Finches and the Galapagos
He was impressed with
Patagonian fossils and the
diversity of life in the
Galapagos Islands.
Darwin was also struck by the fact that there were 14
different species of finches, each with a beak shape
and size that was adapted to its particular ecological
niche.
Darwin’s Theory of Evolution
Years later, Darwin discovered that each
specimen was actually a separate species,
meaning they could not interbreed.
So, even though these species resembled
related species from other parts of South
America, they were still uniquely different.
But how could this be???
Darwin’s Theory of Evolution
Darwin figured that new species could appear
gradually through small changes over time, but
he still couldn’t figure out how it worked.
*Artificial Selection: a process of selective
breeding where the breeder will select animals
with certain traits to breed with others in hopes
of producing offspring with the same traits.
Darwin’s Theory of Evolution
Adaptation: all organisms are suited to their
environments.
Variation: all organisms differ in their traits.
Over-reproduction: all organisms tend to
reproduce beyond their environment's capacity
to support them.
Darwin’s Theory of Evolution
Deduction 1:
Organisms have an enormous capacity to
overproduce.
Deduction 2:
Populations (with a few exceptions) remain
remarkably stable.
Deduction 3:
There must be a struggle for survival.
Darwin’s Theory of Evolution
Deduction 4:
Individuals differ in their characteristics and
many of these differences are heritable
(genetic).
Deduction 5:
Those individuals who possess adaptive
characteristics will reproduce more successfully
than those who don’t AND will pass on these
characteristics to their offspring.
Darwin’s Theory of Evolution
Since not all organisms are equally well adapted
to their environment, some will survive and
reproduce “better” than others -- this is known
as natural selection.
Sometimes this is referred to as "survival of the
fittest.” In reality, this deals with the
reproductive success of the organisms and not
solely their relative strength or speed.
Natural Selection determines the differential
survival of groups of organisms
Evidence of Evolution
Darwin’s Theory of Evolution
Evolution: the result of genetic changes that
occur in constantly changing environments.
The fossil record
Darwin’s Theory of Evolution
Fossils offer some of the most significant
evidence of evolutionary change.
They provide a record of various species that
have lived and died.
They also provide evidence of change.
Darwin’s Theory of Evolution
Ancestral Traits: primitive features
that DO appear in ancestral forms
over time.
Derived Traits: newly evolved
features that do NOT appear in the
fossils of common ancestors.
Homologous Structures: similar structures
acquired from a common ancestor.
Darwin’s Theory of Evolution
Analogous Structures: parts of different organisms
that have similar forms and functions, but different
internal structures (wing of a bird & wing of an insect).
Darwin’s Theory of Evolution
Vestigial Structures: remnants of structures that were
once functional in an ancestral form (appendix, wisdom
teeth, coccyx, nictitating membrane).
Kiwi birds have wings but don’t use them.
The human appendix.
Snakes have a pelvic bone with two hind limb
claws still attached. Snakes have legs?
Bat Wing vs. Bird Wing
Darwin’s Theory of Evolution
Vertebrate embryos provide more glimpses into
evolutionary relationships.
Scientists have found that vertebrate embryos
go through similar cycles during development.
In time they differ, but during the early stages
they look alike.
Darwin’s Theory of Evolution
Adaptation: A trait shaped by natural selection
that increases an organism’s reproductive
success.
An organism’s adaptation is only as strong as
the next generation.
The better an organism is adapted to its
environment, the greater its chances of survival
and reproductive success.
Darwin’s Theory of Evolution
Camouflage: species evolve morphological
adaptations that allow them to blend with their
natural environments.
Camouflage basically lets organisms become
invisible to predators.
Those that hide, survive. Those that survive,
reproduce.
Darwin’s Theory of Evolution
http://science.howstuffworks.com/animal-camouflage2.htm
Frogs have done it.
Birds are doing it.
Even fish have figured it out.
Darwin’s Theory of Evolution
Mimicry: One species evolves to resemble
another species.
*Harmless species tend to take on the traits and
looks of more harmful species, therefore
avoiding predators.
Top: the harmless mimic,
Allobates zaparo.
Middle: Epipedobates
bilinguis, the toxic poison
dart frog that A. zaparo
mimics when all three
frogs occur together.
Bottom: E. parvalus, the
more abundant, more
toxic poison dart frog.
Darwin’s Theory of Evolution
Plants adapt.
Animals adapt.
People adapt.
Disease adapts!
Darwin’s Theory of Evolution
Species of bacteria that originally were killed by
penicillin and other antibiotics have developed
drug resistance.
For every cure there is at least one strand that
cannot be cured.
The more we cure, the more incurable strands
develop.
Other factors within evolution.
Darwin’s Theory of Evolution
Disruptive Selection: a population evolves into two
groups after being split for some reason.
(In these cases, the extremes survive and those in the
middle are wiped out).
Example: Black bunnies, grey bunnies, and white
bunnies live in an area where there is an abundance of
black stones and white stones. The black and white
bunnies will survive, but the grey won’t. Why?
Others adapt certain characteristics that are
more appealing to the opposite sex. This is
called sexual selection.
Darwin’s Theory of Evolution
There are times when unrelated species
evolve similar traits and look alike even
though they are very different.
Convergent Evolution: occurs in
environments that are geographically far
apart but have similar ecologies and
climates.