Download Transitional Fossils

Biological Evolution
Modern humans (Homo sapiens) appear
about 2 seconds before midnight
Age of
reptiles
Insects and
amphibians
invade the land
Plants
invade
the land
Age of
mammals
Recorded human history begins 1/4
second before midnight
Origin of life (3.6–3.8 billion years ago)
Fossils
become
abundant
Fossils
present
but rare
Evolution and
expansion of life
Fossil Record
• Most of what we know of the history of life on
earth comes from fossils (SJ Gould)
• Give us physical evidence of organisms
– Show us internal structure
• Uneven and incomplete record of species
– We have fossils for 1% of species believed to have
lived on earth
– Some organisms left no fossils, others decomposed,
others have yet to be found.
• Other info from ancient rocks, ice core, DNA
• The whale as an example Other evidence
here
4 major mechanisms that drive evolution:
•
•
•
•
Natural Selection
Mutation
Gene Flow
Genetic Drift
Evidence of Evolution
• The Fossil Record
• Geographic Distribution of Living
Things
• Homologous Body Structures
• Similarities in Early Development
Fossils
• The fossil record shows that:
– Things existed in the past that no longer
exist today and
– Things exist today that did not exist in the
past.
• The fossil record is a record of change in
the composition of the biosphere over
time.
What is a fossil?
Fossils are rare
• Most organisms are eaten or decay after
death.
• Fossils only form in places where there
is little erosion: lake bottoms, deep
oceans, etc.
• We have little fossil record of beach
organisms and alpine communities.
Some fossils show transition
• Because fossils are rare, and change
can be rapid, there are few “missing
links” in the fossil record.
• However, some fossil sequences of
marine organisms do show good
evidence of transition from one form to
another.
Transitional Fossils
Adaptations
What are transitional fossils?
• A transitional fossil may be defined as a
fossil which exhibits traits common to both
ancestral and derived groups.
• This is especially important when groups
are sharply differentiated.
• They can show how a species might adapt
to survive their new conditions.
Importance:
• Transitional fossils are often used to test
theories of species development.
• These theories include broad shifts in
habitat use (aquatic to terrestrial
organisms) or shifts in physical
characteristics within a species or group of
species (development of hard shells in
trilobites).
How can I see this now?
• Plants can adapt to change to the
conditions of climate. We see this in
drought resistant plants.
• Transitional fossils are more about the
species natural ability to adapt instead of
the act of genetic engineering (humans
altering a species).
Fish compared to land animal
• The jaws of some fish
might resemble
animals that live on
land, thus leading
some scientists to
believe that some fish
adapted to live on
land.
• Some scientists use
the word evolve for
the word adaptions.
Transitions from pre-mammal to mammal…
Human Adaptations
• Human skulls have increased in size
• Other ways in which humans have
adapted include growth.
• Humans are now much taller today than
they were a hundred years ago.
Comparative Anatomy
• Comparative Anatomy includes Homologous and
Analogous structures as well as vestigial features.
• Comparisons of anatomical features in different
organisms often provides evidence to support the
theory of evolution. As Organisms are often classed
together according to similarities in their structures.
• It was through comparing the anatomy of organisms
that scientist discovered phylogeny, meaning the
evolutionary history of a group of organisms.
“What can be more curious than that the hand of a man, formed for grasping, that of
a mole for digging, the leg of a horse, the paddle of the porpoise, and the wings
of the bat, should all be constructed on the same pattern, and should include the
same bones, in the same relative positions.
-Darwin.
Homologous Structures
• Homologous structure are
structures that share a common
origin but may serve different
functions in modern species.
• These structures are evidence that
organisms with similar structure
evolved from a common ancestor.
• Examples include the forelimbs of a
variety of mammals. For example,
human, cat, whale and bat.
Homologous Structures
• These species show the same skeletal
elements. Is in the humorous, radius and ulna.
• However these skeletal elements have been
modified over time to suit the different
functions suitable for the type of mammal.
• Homologous structures result from divergent
evolution meaning their ancestral lines started
out fairly similar, but evolved along different
paths, becoming more different over time.
• Structures that are similar due to evolutionary origin, such
as the forearm bones of humans, birds, porpoises, and
elephants, are called homologous
Birds and Reptiles
• Both have scales
• Reptile fossils most
common to modern
birds
2017/7/5
Analogous Structures
• Analogous structures are a
contrast to homologous
structures.
• They serve the same
function between organisms
but are different in internal
anatomy.
www.encarta.co
m
 Such as the wings of birds and
butterflies or the eyes of
lobsters and fish.
• These structures are of no
use in classifying organisms
or in working out their
evolutionary relationships
Figure
4
Vestigial Structures
• Refers to an organ or part (for example,
the human appendix) which is greatly
reduced from the original ancestral form
and is no longer functional or is of reduced
or altered function
• Are often homologous to structures that
are functioning normally in other species
• provide a clue to the evolutionary history
of a species because they are remnants of
structures found in the ancestral species.
Embryology
• Different species often have very similar
embryos, even if the adult forms are quite
different.
Video
• http://www.youtube.com/watch?v=kfTbrHg
8KGQ