Transcript Intro to Evolution

Intro to Evolution
Evolution – The process of change over time
The Theory of Evolution suggests that existing forms of
life on Earth have evolved from earlier forms over long
periods of time.
Mrs. Degl
Evidence
Scientists estimate that the Earth is at least as old
as it’s oldest rocks, which are 4.6 billion years old.
Radioactive dating gives us the age of the oldest
rocks.
While studying the rocks of the planet, scientists
have found millions of fossils (the remains or
traces of organisms that no longer exist). By
studying the rocks and fossils, scientists have
developed a picture of the changes that have
occurred on the Earth, and with it’s living
organisms, throughout time.
Mrs. Degl
Mrs. Degl
What is this?
Dunkleosteus (30 ft long; bony skull
shown here is about 1 meter high)
Extinct at the end of the Devonian.
Mrs. Degl
How do fossils form?
• Most fossils are found in sedimentary rock
that was formed at the bottom of water.
• Sediments are formed when water flows
over land and wear away (erodes) the land.
• These sediments then settle to the bottom
of the water (ocean, river, lake).
• They eventually harden (due to the
pressure on them) into rock.
Mrs. Degl
The Fossil Record
The earliest fossils found date back to 3.5 billion years ago.
These are fossils of bacteria. Fossils can be found in
sedimentary rock; preserved in ice, tar or amber; and
sometimes completely mineralized (petrified) bones can be
found in the ground as well.
The Principle of Superposition states
that all rock layers (strata) are older
than the rock layers above them. So,
older fossils are below younger fossils.
Fossils in the upper strata are usually more complex than
what is below them, but also resemble them. This suggests
that there is a link between recent and older forms of life.
Mrs. Degl
Earth’s Geologic History
There are 2 ways to reconstruct the Earth’s past:
1. Absolute Dating: - placing rock layers/fossils in
proper order based on their actual ages. You can assign
each layer an age in years. This is done with radioactive
elements, like carbon.
2.
Relative Dating: - placing rock layers/fossils in
proper order based on their order of formation (Law of
Superposition). You just know which ones are older
and younger than the others. You do not know the exact
age in years, of each layer.
Mrs. Degl
Mrs. Degl
Observations that support the
Evolution Theory have been made
from studies in:
1. Comparative Anatomy (bone
structure study)
2. Embryology (embryo study)
3. Cytology (cell study)
4. Biochemistry (similar DNA, and
enzymes).
Mrs. Degl
Comparative Anatomy
Mrs. Degl
•Evidence supports
that similarities of
basic structures
exist between
different organisms.
•Homologous
structures are
similar anatomical
parts found in
different organisms.
•The presence of
these homologous
structures suggest
that these evolved
from a common
ancestor.
Comparative Embryology
Mrs. Degl
Common ancestor?
Theories of Evolution attempt to explain:
1. Similarities and differences among
species
2. Adaptations
Adaptations are a major component to
evolutionary theories. Adaptations are
features which make a species better
suited to live and reproduce in its
environment.
Mrs. Degl
Spontaneous Generation
Theory
•For many centuries many people believed in the concept of
spontaneous generation, the creation of life from organic matter.
•Louis Pasteur ended the debate with his famous swan-neck flask
experiment, which allowed air to contact the broth. Microbes present in
the dust were not able to navigate the tortuous bends in the neck of the
flask. This cannot happen!
Mrs. Degl
Lamarck’s Theory…Also called “use and disuse”…
Proven NOT TRUE!!... He thought presently used
structures were better developed and passed on…and those
not used disappeared.
Mrs. Degl
NATURAL SELECTION THEORY
• While on the
Galapagos Islands
Darwin studied
finches.
• He noticed that the
finches beaks on all of
the islands were
slightly different and
Darwin wondered why.
• He proposed that
evolution occurred as
a result of NATURAL
Mrs. Degl
SELECTION.
Mrs. Degl
Mrs. Degl
Included in Darwin’s
Natural Selection Theory
were six main ideas:
1. Overpopulation
2. Competition
3. Survival of the Fittest
4. Natural Selection
5. Reproduction
6. Speciation
Mrs. Degl
Overpopulation
• Within a population, there
are more offspring produced
in each generation than can
possibly survive.
Mrs. Degl
Competition
• Natural resources (food,
water, and space) are limited.
• Because there are many
organisms with similar
requirements, there must be
competition between them for
the resources needed to
survive.
Mrs. Degl
Survival of the Fittest
• Variations among members of a
population make some of them
better adapted to the environment
than others.
• It is generally the best-adapted
individuals that will survive. The
ones not very well adapted will die
off.
Mrs. Degl
Natural Selection
•The environment is the agent of natural
selection.
•Meaning, in an environment experiencing a
particularly cold period, the species variation that
has the thicker fur will most likely survive.
•In this case, their variation (thicker fur) is more
helpful for survival and the majority of that
population will have thick fur.
Mrs. Degl
Reproduction
•All species will reproduce.
•The species with the best variation will have a
have a higher offspring rate, because there
would be more of them around to mate.
•What results is the better adapted trait gets
passed down to the future generations while the
less successful variation gets phased out over
time.
•An example is how the thicker furred animal
would produce more offspring in the cold period,
while the thinner furred animal would not.
•This is what causes extinctions.
Mrs. Degl
Speciation
• The development of a new
species occurs as variations or
adaptations accumulate in a
population over many
generations
• Ex: caveman  present man
Mrs. Degl
Right
Wrong
Mrs. Degl