Transcript Evidence of Evolution

Evidence of Evolution
Many of you asked what evidence there is for
evolution. The short answer is that there is a lot
of evidence that supports the theory of
evolution. That’s why it is called a theory and
not a hypothesis. There is evidence of evolution
in homologous structures, embryology, DNA
evidence, and fossils. We will examine each of
these in more detail today.
Review: Natural Selection is the
Mechanism of Evolution
Natural selection is what
makes evolution happen!
Organisms that are more fit
are more likely to survive
and pass on their genes to
their offspring.
The Fossil Record
Fossils are the remains of
ancient life. Different
layers of rock have
formed at different times
during the Earth’s history.
By comparing fossils from
older rock layers with
fossils from younger
layers, scientists
documented the fact that
life on earth has changed
over time.
Geographic Distribution
of Living Species
The distribution of living things on earth provides information
about the past histories of both living things and the surface of
the Earth. This evidence is consistent not just with the evolution
of life, but also with the movement of continental plates around
the world-otherwise known as plate tectonics.
Marsupial mammals are found in the Americas as well as
Australia and New Guinea, shown in brown on the map at right.
They are not found swimming across the Pacific Ocean, nor have
they been discovered in Asia. There appear to be no routes of
migration between the two populations. How could marsupials
have gotten from their place of origin to locations half a world
away?
Fossils of marsupials have been found in the Antarctic as well as in
South America and Australia. During the past few decades
scientists have demonstrated that what is now called South
America was part of a large land mass called Gondwana, which
included Australia and Antarctica. Marsupials didn’t need a
migration route from one part of the world to another; they rode
the continents to their present positions.
Homologous Structures
Homologous structures have
different mature forms, but
develop from the same cell
types in embryos.
The limbs of birds, mammals,
and reptiles have very
different shapes and
functions, yet, they are all
made up of the same basic
bones.
Comparative Embryology
The early stages, or embryos, of
many vertebrates are very similar.
This does not mean that a human
embryo is ever identical to a
chicken or fish embryo. What do
these similarities mean?
It is clear that the same groups of
cells in embryos develop in the
same order and in similar patterns
to produce the tissues and organs
of all vertebrates. These common
cells and tissues, growing in similar
ways, produce homologous
structures.
DNA and Protein Sequence Evidence
All cells use on DNA to make protein, suggesting that this
has been passed down from an ancient common ancestor.
Biologists can study the amino acid sequences in proteins
to determine evolutionary relationships among various
species. Biologists have found that the more closely
related two species are, the more similar the amino acid
sequences of their proteins. Such comparisons allow
scientists to show evolutionary relationships between
different organisms.
Since DNA molecules are highly conserved and passed
from one generation to the next, base sequence pattern
indicates evolutionary relationships. Matches in base
sequence between species show how closely related the
species are. For example, in the picture you can see that
more matches are made between a human and a chimp’s
DNA than between a human and a chicken. This indicates
that the human and the chimp shared a more recent
common ancestor than the human and the chicken, and
are closely related.