Transcript Evidence for Evolution

Evidence of Evolution
Section 13-2
Evolution
Definition: A change in the genetic
makeup of a POPULATION over time.
Evolution
Punctuated
Equilibrium
Gradualism
Evolution
Basic Points agreed upon by most scientists concerning
evolution:
• Earth is about 4.6 billion years old.
• Organisms have inhabited the Earth for most of its
history (about 3.5 billion years ago).
•All organisms living today evolved from earlier,
simpler life-forms.
Fossil Record Evidence
• Fossils offer the most direct evidence that
evolution takes place.
• Currently we have fossils for about 250,000 species.
Fossil Record Evidence
• We will never be able to recover fossils for most of
the now-extinct species, so our “record” of the
past is incomplete, with built-in biases.
• The completeness of the fossil record varies as a
function of the kinds of organisms represented,
where they lived, and the stability of their burial
sites.
• Organisms with hard exoskeletons (crab), lived in a
shallow sea, and produced a lot of offspring have the
best chance of becoming a fossil.
Fossil Record Evidence
Fossil: preserved remains of ancient organisms
• Fossils are made when settling particles cover the
remains of dead organisms in places where conditions
are perfect for their survival over time (places with a
lot of sedimentary rock).
Comparative Studies:
Comparative Anatomy
Comparative Studies:
Comparative Anatomy
• Comparisons of the anatomy of different
types of organisms often reveal basic
similarities in body structures, even though
their functions may be very different.
Comparative Anatomy:
Homologous Structures
Comparative Studies:
Comparative Anatomy
• Homologous structures: similar arrangement of
bones in a structure
•Ex. Forelimbs of a penguin, alligator, bat, human
• The limbs look different and vary greatly in function, but
are very similar in skeletal structure and derive from same
structures in the embryo.
• The presence of homologous structures indicates that
the species shared a fairly recent common
ancestor.
Comparative Anatomy:
Analogous Structures
• Analogous structures: features serve identical
functions and look somewhat alike, but no common
ancestry
•Ex. Wings of hummingbird and humming moth
Comparative Anatomy:
Vestigial Structures
• Vestigial structures: structures with no real
purpose that are left-over from an organism’s
evolutionary past
•Ex. Whale pelvis, human appendix
Comparative Embryology
Comparative Embryology
• Human embryos and embryos of all other vertebrates
are similar during early development and then
take on characteristic adult form.
• The early embryos of vertebrates strongly resemble
one another because they have inherited the same
ancient plan for development.
Comparative Biochemistry
Comparative Biochemistry
• If species have changed over time, then the genes
that determine their characteristics should also have
changed.
• So genes of closely related species will show more
similarities in nucleotide and amino acid sequences
• Ex. Hemoglobin, cytochrome c
• It is at the level of DNA that changes/variation
occurs—a result of mutation.
Which of the types of evidence
for evolution presented to you
today is most convincing??
Why???