Evidence for Evolution

Review (what we’ve learned so far)
 Mutations and sexual reproduction/
crossing over provide variability within
species.
 Some traits give individuals within a
species an advantage - those
organisms live longer and/or reproduce
more = natural selection
 Over time, the population shifts so that
all (or most) individuals have this trait =
adaptation
 Evolution of a whole new species
(speciation) takes long periods of time
Main evidence for evolution
Fossils
Geographic distribution of organisms
around the world
Artificial selection
Homologous structures
Vestigial structures
Embryology
Comparative analysis of DNA
Fossils

The bulk of our
understanding about
ancient life
 Bacterial cells to complete
T-Rex skeletons
 How are fossils formed?
(Short video)


http://www.teachersdomain.org/68/sci/life/div/becfossil/index.html
http://kcts9.pbslearningmedia.org/
resource/tdc02.sci.life.evo.becfos
sil/becoming-a-fossil/
Fossil Questions
How are fossils formed?



Organism dies and is covered by sediments
(mud, sand, silt, clay, ash)
Calcium in bones replaced by minerals in
the sediments over time
Sometimes imprints can also be preserved
(tracks, leaf impressions, etc.)
It’s a pretty rare event to find complete fossils in good condition. After millions
of years any number of things could happen to destroy fossils before they are
discovered and documented by scientists, if the animal even fossilizes at all.
Finding well preserved baby animals is particularly hard, since they are more
likely to have gotten trampled or eaten after their death. Phillip Currie from the
University of Alberta has recently uncovered a juvenile Chasmosaurus belli that
was so complete and intact, he was actually able to speculate about the cause
of death.
The fossil was found in what used to be a riverbed. This has led Currie and his
research team to believe that the baby didn’t die at the hands of a larger
creature. It most likely wandered out too far into the water and got caught in the
current. Unable to save itself, it drowned and settled at the bottom of the river,
where it would eventually become fossilized in the sediment. The body was so
well preserved, Currie was actually able to see impressions from the baby’s
skin in the surrounding rock.
Why do most living things not
leave fossils behind?
 Organism was eaten
 Didn’t die in correct environment to be
preserved
 Body has no ‘hard parts’ (shell, skeleton)
•
Virtually absent from fossil record: flatworms,
jellyfish, sea slugs, etc.
How are fossils uncovered?


Erosion brings fossils back to surface
Humans dig to find fossils
•
Determine specific locations that are likely spots
to hold fossils
How do scientists determine the
age of fossils?
Technique known as:
Radiometric Dating
http://www.teachersdomain.org/6-8/sci/life/div/radiodating/index.html
http://kcts9.pbslearningmedia.org/resource/tdc02.sci.phys.matter.radiodating/radiometricdating/
Transitional
Fossils

a.k.a. Intermediate
fossils
Important because they:
 Provide a link
between past forms of
an organism
Transitional Fossils: Orca example

1.
2.
3.
4.
We’ve believed for a long time that
whales (and seals, otters, etc) were
mammals because they share COMMON
FEATURES with land mammals
Warm-blooded (endothermic)
Give live birth and provide milk for young
Have hair
Similar respiratory, circulatory, nervous,
and digestive systems
Transitional Fossils
whales evolution example:
Modern whale – totally aquatic
 Nostrils on top of head = blowhole
 Tail evolved into flipper
 Ears modified directional hearing underwater
Basilosaurus – aquatic
 flippers & long, flexible body
 small, weak hind legs
 Nostrils on top of head
Ambulocetus – amphibious (both land and water)
 Forelimbs equipped with fingers/small hooves
 Hind feet & tail adapted for swimming
 Nostrils on top of snout
Mesocynids– terrestrial
 Tetrapod – limbs adapted to moving on land
 Ears adapted to hearing in air
 Nostrils in front of snout
What is this picture of??
 Are
you 100%
sure?
What is this picture of??
 Are
you still
100% sure?
 Can
we ever
truly fill in all
of the gaps??
Gaps in Fossil Record
 We
have fossils for 350,000 species of
ancient organisms…

That’s only a tiny fraction of total number of
species that have ever lived!!!!!
 We
fill in the ‘gaps’ using logical reasoning
as well as other lines of evidence
Embryology
 Early
stages of related animals are very
similar
 Similarity in the development from egg to
adult form (ontogeny) is evidence of
common ancestry

More similarity in ontogeny = more recent
common ancestor (more closely related)
Comparative Embryology of Vertebrates
Which one is the human? The rabbit?
The fish? The salamander? The
tortoise? The hog? The calf?
Comparative Embryology of Vertebrates
So when do organisms begin to look
different? During _______?
HUMAN
Comparative Embryology of Vertebrates
Which two seem more genetically
related/separate from the others?? How do
you know?
Geographic Distribution on
Organisms around the world



Similar environments around
the world contain organisms
that are DIFFERENT species
but have similar anatomies
and/or behaviors because…
similar selective pressures
lead to common structures
and or behaviors that aid
survival and/or reproduction
Example: meerkats and
prairie dogs
Another example of
similar geography
resulting in similar
structure in unrelated
organisms:
Beaver
Muskrat
Beaver
and
Muskrat
Coypu
Capybara
beavers,
muskrats,
coypus,
& capybaras
Coypu
and
Capabara
Geographic Distribution, cont.

Additionally,
organisms from a
common ancestor will
change in structure
and function to adapt
to a new, specific
environment (niche)
 Prime example:
islands!

the more isolated the
island, the more
distinct its organisms
Artificial Selection

When humans breed organisms with desired
trait repeatedly until desired characteristic is
obtained.
 Plant and animal breeders have long taken
advantage of the heritability of traits to improve
crops and livestock and pets
 Humans use the same mechanisms to change
organisms that nature uses


Artificial – humans ‘select’ the best traits
Natural – nature ‘selects’ best, or ‘most fit’ traits
Artificial Selection Examples
Hundreds of varieties of
peppers – all originated
from an initial species
Different breeds
of dogs and cats
‘created’ by man
by selecting for
desirable traits
(fast, sociable,
good smell,
short fur, etc.)
Homologous Structures

Similar structures in a variety of different
organisms
 Shared trait(structure) provides evidence that
the organisms had a shared common ancestor
with that trait
Example:
Homologous
bone
structure in
forelimbs of
all mammals
Vestigial Structures
As species evolve over time… some structures become
unnecessary to survival of organism
 Over time become reduced (vestiges)
 Eventually disappear
Examples:

Human Tailbone (coccyx)
- These fused vertebrae are the only vestiges
that are left of the tail that other mammals still use for balance, communication, and in
some primates, as a prehensile limb. As our ancestors were learning to walk upright,
their tail became useless, and it slowly disappeared.
Hind Leg Bones in Whales
Comparative Analysis of DNA
If all organisms evolved from same original
ancestors (3.5 bya), then all should share
some common DNA
 YES! all life shares same general
machinery for regulation of cell division,
building cell parts, etc.
 Greater DNA similarity between 2 species
= more recent common ancestor