Transcript Evidence for Darwin`s Theory of Evolution

Evidence for Darwin’s
Theory of Evolution
Why Do Scientists Accept It?
The Evidence Falls Into Several
Categories
 Structural Adaptations
 Physiological Adaptations
 Fossils
 Anatomy
 Embryology
 Biochemistry
Adaptations
 An adaptation is any variation that aids an
organism’s chances of survival in its
environment.
 Structural adaptations: mole-rats have
adaptations to live underground that have
evolved over millions of years (large teeth,
large claws). Other examples? Thorns of
plants and porcupine’s quills.
Mimicry and Camouflage
 Mimicry: One species evolves to look like another.
Harmless scarlet king snake looks like poisonous
coral snake. Predators avoid both.
Or, several harmful species evolve to resemble each
other – bees, wasps, yellow jackets.
 Camouflage: Organism blends into its background.
Predators don’t notice it. Can you give examples?
Physiological Adaptations
 Many bacteria have evolved to be resistant to
penicillin which was a “wonder” drug 50
years ago.
 This change in the bacteria’s metabolic processes
happens much faster than structural adaptations.
 Insects and weeds are also evolving resistances to
chemicals used to control them.
Other Evidence
 Fossils – Fossil record is incomplete, but still
provides extensive evidence. Paleontologist have
traced the evolution of the modern camel. (See
page 408 in your text.) 66 million years ago the
ancestors of camels were as small as rabbits.
 Anatomy

Homologous structures – Structural features that
serve different purposes but have a common
evolutionary origin. Example: Bones modified for
function, but basic arrangement is similar. See the
whale forelimb, crocodile forelimb and bird wing on
page 409.
More Anatomical Evidence

Analogous structures: Body parts that are similar in
function, but do not have common evolutionary
origin. These adaptations evolved separately in
different groups of organisms. Wings are a good
example. (Birds, butterflies, insects)

Vestigial structures: Body structure that has no
function but was probably useful to an ancestor.
Examples: hind limbs in whale and snake, wings of
ostrich, eyes of cavefish
Still More Evidence…
 Embryology – Similarities among young
embryos suggests evolution from a distant,
common ancestor. See the embryos of a fish,
a reptile, a bird and a mammal on page
410.They all have tails and gill slits.
 Biochemistry – Comparison of DNA or RNA
of different species provides biochemical
evidence for evolutionary relationships.
Scientists use this data to construct
evolutionary diagrams (see page 411).