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Transcript
Changes Over Time
Chapter 7
Who is Charles Darwin?
• Naturalist who traveled
the world in the 1830’s
• Observed similarities and
differences between
species in South America
and the Galapagos Islands
• Wrote a book called “The
Origin of Species”
• Formed the theory of
evolution through natural
selection.
What is Evolution?
As a WORD
As a THEORY
• A gradual change • All species have
evolved from a
in a species over
common ancestor.
time.
• There is a lot of
• Most people
controversy over
agree with this
this idea.
idea.
What Words to Know?
• Species- A group of similar organisms that
reproduce and create offspring that can reproduce.
• Adaptation- A trait that helps an organism survive
in its environment.
• Natural Selection- A process where individuals
from a species are better adapted to their
environment, and survive longer to reproduce and
pass on their good genes.
http://www.sciencenetlinks.com/interactives/evolutio
n.html
How does Natural Selection Work?
Most species produce
more offspring than
can possibly survive
Offspring that are better adapted,
survive and reproduce, thus
passing on their genes to the next
generation
Food and resources are
limited, so offspring
compete to survive
Offspring have variations
that make some better
adapted to their environment
What leads to Natural Selection?
• Overproduction- producing far more
offspring than can possibly survive.
• Competition- Limited resources (food,
space, etc.)
• Variations- Differences between members
of a species.
• Selection- Variations that make individuals
more adapted to environment (helpful
variations).
What Causes Variations?
• Mutations- Changes in genes or
chromosomes.
• Only traits that are inherited or
controlled by genes can create variations
and be acted on by natural selection.
How do New Species Form?
• Natural disasters, rivers, canyons, mountain
formations, and human disruptions can lead
to isolation within a species.
• When a group of individuals
from a species remains separate
long enough, different traits evolve.
What is Geographic Isolation?
• The theory that the continents started as one large
land mass or supercontinent called Pangaea.
• Over millions of years the one continent split apart
isolating individual groups of the same species.
http://pubs.usgs.gov/publications/text/historical.html
How Fast does Evolution
Occur?
• Two Theories
• Some scientists believe that both occur
• Gradualism and Punctuated Equilibria
What is Gradualism?
• Gradualism – A theory that evolution
occurs slowly but steadily over time
(Darwin agrees with this theory)
What is Punctuated Equilibria?
• Punctuated Equilibria – A theory that species
evolve during short periods of rapid change
• Short bursts with long periods of stability between
• This theory explains the absence of intermediate
fossils in branches of evolution
What Evidence is there for
Evolution?
• The fossil findings and the fossil record
(most evidence)
• Similarities in body structure (homologous
structures)
• Similarities in DNA (widely used today)
What are Fossils?
• A fossil is the preserved remains or traces of an
organism that lived in the past.
• A fossil can be formed from a bone, tooth, shell,
or other part of an organism.
• Other fossils can be traces of the organism, such
as footprints or worm burrows left in mud that
later turned to stone.
How do fossils form?
• Organism gets buried in
sediment, tar pits, ice, or sap
(amber).
• Form from a bone, tooth, shell,
leaves, stems, roots, seeds,
prints, or other parts of an
organism
• Petrified Fossils= remains turn
to rock
• Molds= remains dissolve and
leave a hollow space.
• Cast= mold filled with
minerals.
• Fossil Fuels = forests that are
buried and under extreme
pressure for millions of years
form coal (carbon).
How Do You Determine
a Fossils Age?
• Relative Dating =
Date a fossil relative to other
things around it
Used to determine which of
the 2 fossils is older.
Example: Fossils found in
rock layers
Not used to find actual age of
fossils
• Absolute Dating =
Used to determine the actual
age of a fossil.
Example: Comparing the
amount of radioactive
elements in rock where
fossil is found to the
amount of element it
breaks down into.
CARBON DATING
What do Fossils Reveal?
• History of Earth, Fossil Record includes millions
of collected fossils, but is incomplete.
• The structure of extinct animals, fossils are used to
build models of animals.
• Clues as to how and when organisms evolved.
What are Homologous Structures?
• Similar structures that related species have
inherited from a common ancestor
• Similarities provide evidence that certain
organisms all evolved from a common
ancestor
What is Embryonic Development?
• Looking at the changes of an organisms
fetus while still in the womb
• Different embryos are compared during
development, the more similarities, the
more closely related
What is the Geologic Time Scale?
• A “calendar”, a timeline of Earth’s history.
• Spans more than 4.6 billion years
• Longest span of time is Precambrian, the
first 4 billion years (not many fossils)
• Paleozoic, Mesozoic, and Cenozoic make
up the last 0.6 billion years and are divided
into eras and periods
Geologic Time
Scale:
How do Scientist Show
Evolutionary Relationships?
• Branching Tree or Cladogram- a diagram that shows
evolutionary relationships between different species.
Fossil Websites
http://www.bbc.co.uk/beasts/
fossilfun/
http://www.rom.on.ca/quiz/f
ossil/
http://dsc.discovery.com/con
vergence/dinosaurplanet/i
nteractive/interactive.html
• http://www.fieldmuse
um.org/sue/whosue.ht
ml
• http://ology.amnh.org/
paleontology/fightingd
inos/index.html