Download 2-evidence-for

Evidence for Evolution
Subtitle
The Fossil Record
• Fossils are preserved remains of
ancient organisms and are usually
found in sedimentary rocks. The
layers of rock follow a geological
time scale where the lower layers of
rock are older than the upper layers
of rock, as long as they haven’t been
disturbed through earthquakes or
tectonic plate movement.
• Since the lower layers of rock are
older, scientist can determine the
sequence of changes in an organism
based on the fossils found in
different layers
• This picture shows the changes in a single species of snail. (Many of
the forms are now extinct.)
DNA & Embryology
• Similarities in the structure and development of embryos provide evidence of
descent from a common ancestor.
• During the embryonic development stage very
different species show similarities. These
similarities during certain embryological stages
indicate that similar genes are at work.
• The genes that are active during early
development of fish, birds, humans and related
animals all shared a common ancestor whose
particular sequence of genes controlled its
early development.
• Much like the development of today’s
organisms mentioned above. This particular
sequence of genes has thus been passed on to
the species that descended from it.
• As the embryos grow and develop the embryos become more and more
different.
• These differences are caused by genes that have changed over the
course of evolution (through mutation).
• If the organism survives then the DNA, or genetic code, is passed along
to surviving offspring.
• All organisms share many biochemical compounds and they all use DNA
and or/RNA as the genetic code to pass on genetic information from on
generation to the next and to control growth and development.
• Therefore the more closely related two species are, the more closely
their chemical compounds, such as DNA, resemble each other.
Comparative Anatomy– Homologous Structures
• The evolutionary relationships between groups of organisms are
determined mainly by structural similarities called homologous
structures.
• These homologous structures suggest that these organisms all
descended from a common ancestor.
• For example the bones of the forelimb of air-breathing vertebrates
are composed of similar bone arrangements in a comparable
pattern.
Analogous Structures
• Some organisms have structures that are similar in appearance and function, but they
have different origins.
• They usually have very different internal structures. These structures are called
analogous structures.
• For example, birds, butterflies and bats all have the ability to fly using wings. However
when look closer at the structures of these wings you will see that the internal
structures are completely different. A butterfly’s wing is made of thin nonliving
membranes, a birds wing is made of skin, muscles and bones; and a bats wing is made of
skin stretched between elongated finger bones.
Vestigial Organs
• Some organisms have organs or
appendages that don’t have any
apparent purpose.
• These are called vestigial organs.
Many of these organs or
structures are “leftover” from
previous ancestors.
• For example, humans have an
appendix that serves no purpose
in digestion today. However, a
large functioning appendix is
found in animals that primarily
eat plant materials, such as the
koala.