Ch 16 Darwin*s Theory of Evolution

1 Review Why are fossils important evidence for
Interpret Visuals use the figure on pg 394-395 to
describe how a modern mystcete whale is different
from Ambulocetus
2 Explain what is the relationship between Hox genes
and embryological development
Draw Conclusions Organisms A and B have very
similar Hox genes, and their embryos, in early
development, are also very similar. What do these
similarities indicate about the ancestry of organisms
A and B
3 Explanation In your own words, write a paragraph
that explains how evidence since Darwin’s time has
strengthened his theories.
16.4 Evidence of Evolution
The fields of geology, physics, paleontology,
chemistry, and embryology, did not have the
technology or understanding to test Darwin’s
assumptions during his lifetime
Genetics and molecular biology didn’t exist.
In the 150 years since Darwin published On the
Origin of Species, discoveries in all these fields
have served as independent tests that have
supported Darwin’s ideas about evolution.
Study of where organisms live now and where they
and their ancestors lived in the past.
Closely Related but Different
Biogeography of Galapagos species suggested that
populations on the island had evolved from
mainland species
Natural selection on the islands produced
variations among populations that resulted in
different, but closely related, island species.
Distantly Related but Similar
Rhea, Ostriches, and Emus
Differences in body structures provide evidence
that they evolved from different ancestors
Similarities provide evidence that similar selection
pressures had caused distantly-related species to
develop similar adaptations.
The Age of Earth and Fossils
Fossils form series that trace the evolution of
modern species from extinct ancestors.
The Age of Earth
Evolution takes a long time
Hutton and Lyell argued that Earth was indeed very
old, but couldn’t determine just how old
Geologists use radioactivity to establish the age of
certain rocks and fossils which indicates the Earth
is about 4.5 billion years.
Recent Fossil Finds
Since 1859 MANY more fossils have been found
Page 394-395.
Limb structure suggests
that these animals
could both swim in
shallow water and walk
on land.
The hind limbs were short
and probably not able to
bear much weight
Spent most of their time in
Streamlined body and
reduced hind limb. suggest
it spent its entire life
swimming in the ocean.
Retain reduced pelvic bones
and some even upper and
lower limb bones
No longer play a role in
Comparing Anatomy and Embryology
Homologous structures adapted to different
purposes as the result of descent with
modification from a common ancestor.
Homologous Structures
Similar structures that may serve different
functions in various organisms.
Analogous Structures
Body parts that share a common function, but not
 Wing
of a bee and a wing of a bird.
Vestigial Structures
Inherited from ancestors, but have lost much or all
of their original function due to different selection
 Hipbones
of bottlenose dolphins
 Wings of flightless cormorant .
Early developmental stages of many vertebrates
look very similar
Same groups of embryonic cells develop in the
same order and in similar patterns to produce
many homologous tissues and organs in
Life’s Common Genetic Code
All living cells use information coded in DNA and
RNA to carry information from one generation to
the next and to direct protein synthesis.
Homologous Molecules
Many different organisms share homologous
Hox gene.
Testing Natural Selection
Grants tested the Galapagos finches.
Two Testable Assumptions
There must be enough heritable variation in beak
size and shape to provide raw material for
natural selection
Differences in beak size and shape must produce
differences in fitness.
Used medium ground finch on the island of Daphne
 Supports
good-sized finch populations
 Allows them to catch, tag, and identify nearly every
bird of the species.
Periodically recapture the birds
Record which individuals are alive and which have
died, which have reproduced and which have not
Record anatomical characteristics like wing length,
leg length, beak length, beak depth, beak color,
feather color, and total mass of each bird.
When food becomes scarce during dry periods,
birds with the largest beaks are more likely to
The Grants have documented that natural
selection takes place in wild finch populations
frequently, and sometimes rapidly
Without heritable variation in beak sizes, the
medium ground finch would not be able to adapt
to feeding on larger, tougher seeds during a
Like any scientific theory, evolutionary theory is
constantly reviewed as new data are gathered
There is significant uncertainty about exactly how
life began
Questions that remain are about how evolution
works - not whether evolution occurs.
Competition and environmental change drive
natural selection
Traits that don’t matter much under one set of
environmental conditions became adaptive as the
environment changes during a drought.