Transcript Section 16.4

Lesson Overview
Evidence of Evolution
Lesson Overview
16.4 Evidence of Evolution
Lesson Overview
Evidence of Evolution
Biogeography
– study of where organisms
live now and where they and
their ancestors lived in the
past.
– Two biogeographical patterns
are significant to Darwin’s
theory.
1. a pattern in which closely
related species differentiate
in slightly different climates.
Ex. variation in shell shape
among the giant land
tortoises that inhabit the
Galápagos islands.
Lesson Overview
Evidence of Evolution
Species Vary Globally
2. a pattern in which very distantly related species
develop similarities in similar environments.
Ex. similar ground-dwelling birds (rheas, ostriches, and
emus) inhabit similar grasslands in Europe, Australia,
and Africa.
emu.
Rheas
ostriches
Lesson Overview
Evidence of Evolution
Homologous Structures
– Structures shared by related species and that have been
inherited from a common ancestor are called homologous
structures.
– Darwin proposed that animals with similar structures evolved
from a common ancestor
– Biologists test whether structures are homologous by
(1)studying anatomical details the way structures develop
in embryos,
(2)the pattern in which they appeared over evolutionary
history.
Lesson Overview
Evidence of Evolution
Homologous Structures
–Ex. the front limbs of reptiles
and birds are more similar to
each other to than either is to the
front limb of an amphibian or
mammal.
–Scientists say that this similarity
is used to show that the common
ancestor of reptiles and birds
lived more recently than the
common ancestor of reptiles,
birds, and mammals.
Lesson Overview
Evidence of Evolution
Analogous Structures
–Another example used by
scientists are analogous
structures  body parts that
share a common function, but
not structure.
–Ex. The wing of a bee and
the wing of a bird are
analogous structures.
Lesson Overview
Evidence of Evolution
Vestigial Structures
–inherited from ancestors, but
have lost much or all of their
original function due to
different selection pressures
acting on the descendant.
–Ex. The hipbones of
bottlenose dolphins
Pelvic bone of a whale
Lesson Overview
Evidence of Evolution
Other Examples of Vestigial Structures
–The wings of a
flightless cormorant
–The legs of an Italian
three-toed skink
cormorant
three-toed skink
Lesson Overview
Evidence of Evolution
Embryology
–Some scientists use the
similar patterns of
embryological
development as
evidence that organisms
have descended from a
common ancestor.
Lesson Overview
Evidence of Evolution
Life’s Common Genetic Code
– Some scientists believe that the strongest
evidence supporting evolutionary theory
comes from genetics.
Lesson Overview
Evidence of Evolution
Life’s Common Genetic Code
– This genetic code is nearly similar in almost all
organisms, including bacteria, yeasts, plants, fungi,
and animals
– This compares a small portion of the DNA for the
same gene in three animals—a mouse, a whale, and
a chicken.