Transcript CH. 22 Evidence for Evolution

Chapter 22
Evidence for Evolution
Evolution occurs by
natural selection…
 Darwin’s
finches
 Found on
Galapagos
 Descent with
modification
Natural selection has 3
conditions that must be met:
 1.) variation within the population
 2.) variation must lead to differences
among individuals in survival and
reproductive success
 3.) variation must be genetically
inheritable
Found with finches:


variation is within the population
changed from one year to the next depending
on the weather and plant seed production
 drought = fewer seeds, birds with large beaks
survived b/c could eat bigger seeds
 wet = many more small seeds, birds with small
beaks survived ok
 Traits were passed down according to those
who survived – fluctuated within the population
Peppered moths and
industrial melanism
 Industrial melanism is
the darkening of a
species due to industry
 Two main forms:
peppered and melanic
 In areas of industry, the
tree bark is darker – the
dark moths do better
 Non-industrial areas, the
light moths do better
 Kettlewell –did experiment with industrial
melanism
 Raised both colors of moths
 Marked their abdomens and released equal
amounts of each color into an area of industry
and a rural area.
 Waited a a few weeks and recaptured as many
moths as possible in each area.
 Results:
 light moths more in rural area
 dark moths more in industrial area
Artificial Selection
 Lab experiments:
 Used to test if selection can produce
evolutionary change…
 Used fruit flies
 Chose flies with many bristles - Only bred
the ones with the most
 Over 86 generations, increased the
bristle # from 9 to over 40!!
In Agriculture…
 Only allow the
plants that
produce the best
seeds to breed
 Ex: corn, wheat,
strawberries
Domestication…
 Taking a once wild
animal and breeding
those with desirable
traits to eventually
spawn a desirable
offspring
 Has been done with
wolves, foxes, cats
and more!
The fossil record…
 Most direct evidence for evolution
 Can get from rock, amber, permafrost, dry
caves or deserts
 Problem: fossilization does not occur easily!
 Must have very specific conditions
 Usually the remains are scavenged or eroded
before the process can be completed
 Must have very
specific conditions
 Usually the remains
are scavenged or
eroded before the
process can be
completed
 Here’s a bird in the
process of being
fossilized!
Dating fossils
 Date the rocks in which they are
preserved:
 Absolute dating – uses U238
 Relative dating – uses rock layers
in respect to one another
Gaps in the record
 Even though gaps
exist, links have
been found
between:
 Reptiles and
birds
 Ex:
Archaeopteryx
Snakes and
lizards
- pelvic girdles still
visible in snakes
Whales and land
mammals
- flippers with
homologous
structures, pelvic
girdle
Anatomical record
 Homology – homologous
structures are structures
with different
appearances and
functions that are all
derived from the same
body part in a common
ancestor
 Ex: forelimbs of
mammals
Vestigial Organs Rudimentary
structures of
marginal, if any, use.
Human Example
Evolution Viewpoint
 Remodeling of ancestral structures
as their functions or adaptations
changed.
Comparative Embryology
 Problem - closely related organisms go
through similar stages in their embryonic
development.
 Ex: Gill pouches in vertebrates
Molecular Biology
 Study of Evolution at the DNA or protein
levels.
 Problem - related species have similar
DNA sequences.
Evolution Viewpoint
 Related species share a common
ancestrial DNA. The closer the
relationship, the more similar the
DNA sequences should be.
Convergent evolution
Horse evolution…
 For example, we can trace the evolution
of the modern horse through fossils.
 First horses:
 small, short legs, broad feet
 lived in woods and ate leaves and
berries
We will look at the changes in these
animals…
Size
 First horses were the size of dogs or
smaller
 Now they weigh on average about
1000 lbs!
 Let’s see the fossils for this
change…
 http://chem.tufts.edu/science/evoluti
on/HorseEvolution.htm
Toe reduction
 Primitive horses had
4 toes with fleshy
pads like a dog’s
 Modern horses have
one toe encased in
bone and keratin
 This allowed the
horse to run faster
for longer distances
 First row = forefoot
 Bottom row =
hindfoot
Tooth size and shape
 Primitive horses had small and simple
teeth for the vegetation of the time
 Modern horses now have more complex
teeth that are longer and have ridges for
chewing grasses which evolved along
with the horse
 The grasses are tough and the teeth
need to tough to withstand the chewing
of these materials
 Only one genus of horse still exists
today…Equus
 All others died out long ago –
naturally selected against in the
changing environment
Summary
 Know Darwin’s “facts” and “inferences”.
 Be able to discuss the various evidences
of Darwinian evolution.