EVIDENCE FOR EVOLUTION
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Fossil
Biogeographical
Anatomical
Embryological
Biochemical
Vestigial features
Fossil Evidence:
 Fossils are relics or impressions
of ancient organisms
 Most fossils are found in layers (strata) of
sedimentary rock
 The fossil record traces history of life and allows
us to study history of particular organisms
 Through radioactive dating, geologists estimate
the age of the earth at about 4.6 billion years
 Fossils are at least 10,000 years old and include
skeletons, shells, seeds, insects trapped in amber,
imprints of organisms, organisms frozen in ice
(wooly mammoth), or trapped in tar pits (sabertoothed tiger) http://www.tarpits.org
 Transitional forms reveal links between groups
(Example: Therapsids were mammal-like reptiles
and Pterosaurs were bird like reptiles)
Biogeographical Evidence:
 Biogeography is the study of the geographic
distribution of life forms on earth
 Physical factors, such as the location of
continents, determine where a population can
spread
 Example: Placental mammals arose after Australia
separated from the other continents, so only
marsupials diversified in Australia
KOALA
KANGAROO
Anatomical Evidence:
 Organisms have anatomical similarities when
they are closely related because of common
descent
 Homologous structures in different organisms are
inherited from a common ancestor. They have
similar structures but can differ in function
 Example : Vertebrate
Forelimbs contain the
same sets of bones
organized in similar ways,
despite their dissimilar functions. Ex human,
horse, frog, and porpoise.
 Analogous structures are inherited from different
ancestors but resemble each other because they
serve a similar function.
 Example: Bird wing & bat wing are both for flight
but they are structurally different
 Vestigial Structures are remains of a structure that
is no longer functional but show common
ancestry
 Example: Humans have a tailbone but no tail
Embryological Evidence:
 During development, all vertebrates have a post-
anal tail and paired pharyngeal pouches
 Organisms that show similarities in their
embryonic development may have a common
ancestry
Biochemical Evidence:
 Almost all living organisms use the same basic
biochemical molecules, e.g., DNA, ATP, enzymes
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 Similarities in amino acid sequences, DNA codes,
etc. can be explained by descent from a common
ancestor
 Immunological evidence...common reactions to
antigens can indicate an evolutionary relationship
Did you know that.....
Appendix
Appendix
 No known use in modern humans
 Often removed when it becomes infected
 Speculation: once helped to process cellulose in leaf-
rich diet
 Natural selection  smaller appendices (less likely to
become inflamed and diseased)
Coccyx
Coccyx (tail bone)
 Over time we lost the need for a tail (as tree swinging
was replaced by hanging out at the local water hole
grunting Neanderthal gossip)
 Coccyx now functions as a support structure for
various muscles and support when you sit down and
lean back
Darwin’s Point
plica semilunaris
Darwin's Point
 The point (shown in the picture above) is a small thick
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nodule at the junction of the upper and middle
sections of the ear.
Likely used to help focus sounds in animals
No longer has a function in humans
Only 10.4% of the human population still has this
visible left-over mark of our past
It is possible that a much larger number of people
carry the gene that produces it as it does not always
cause the ear tubercle to appear
Third Eyelid
Third Eyelid
 If you watch a cat blink, you will see a white membrane
cross its eye – that is called its third eyelid
 It is quite a rare thing in mammals, but common in
birds, reptiles, and fish
 Humans have a remnant (but non-working) third
eyelid It has become quite small in humans, but some
populations have more visible portions than others
 There is only one known species of primate that still
has a functioning third eyelid, and that is the Calabar
angwantibo which lives in West Africa.
Wisdom Teeth
Wisdom Teeth
 Early humans ate a lot of plants – and they needed to eat
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them quickly enough that they could eat a sufficient
amount in one day to get all of the nutrients they needed
Extra set of molars  more productive
Particularly essential as the body lacked the ability to
sufficiently digest cellulose
As evolution made its selections, our diets changed, our
jaws grew appropriately smaller, and our third molars
became unnecessary
Some human populations have now all but completely
stopped growing wisdom teeth, while others have almost
100% likelihood of developing them.
Plantaris Muscle
Plantaris muscle
 The plantaris muscle is used by animals in gripping
and manipulating objects with their feet – something
you see with apes who seem to be able to use their feet
as well as their hands
 Humans have this muscle as well, but it is now so
underdeveloped that it is often taken out by doctors
when they need tissue for reconstruction in other
parts of the body
 The muscle is so unimportant to the human body that
9% of humans are now born without it.
Extra Ear Muscles
Auriculares muscles
Auriculares muscles
 Also known as the extrinsic ear muscles, the auriculares
muscles are used by animals to swivel and manipulate their
ears (independently of their head) in order to focus their
hearing on particular sounds
 Humans still have the muscles that we would once have
used for the very same reason – but our muscles are now so
feeble that all they can do is give our ears a little wiggle
 The use of these muscles in cats is very visible (as they can
nearly turn their ears completely backwards) – particularly
when they are stalking a bird and need to make the
smallest movements possible so as to not frighten its future
meal.
Junk DNA
L-gulonolactone oxidase
L-gulonolactone oxidase
 While many of the hangovers from our “devolved” past are
visible or physical, this is not true for all. Humans have
structures in their genetic make-up that were once used to
produces enzymes to process vitamin C (it is called Lgulonolactone oxidase)
 Most other animals have this functioning DNA but at some
point in our history, a mutation disabled the gene – whilst
leaving behind its remnants as junk DNA
 This particular junk DNA indicates a common ancestry
with other species on earth, so it is particularly interesting.
Jacobson’s Organ
Vomeronasal organ
Jacobson's organ
 Jacobson’s organ is a fascinating part of animal anatomy and it
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tells us a lot about our own sexual history
The organ is in the nose and it is a special “smell” organ which
detects pheromones (the chemical that triggers sexual desire,
alarm, or information about food trails)
It is this organ that allows some animals to track others for sex
and to know of potential dangers
Humans are born with the Jacobson’s organ, but in early
development its abilities dwindle to a point that it is useless
Once upon a time, humans would have used this organ to locate
mates when communication was not possible. Single’s evenings,
chat rooms, and bars have now taken its place in the process of
human mate-seeking.
Goose Bumps
Cutis Anserina
Goose Bumps
 Humans get goose bumps when they are cold, frightened, angry,
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or in awe
Many other creatures get goose bumps for the same reason, for
example this is why a cat or dog’s hair stands on end and the
cause behind a porcupine’s quills raising
In cold situations, the rising hair traps air between the hairs and
skin, creating insulation and warmth
In response to fear, goose bumps make an animal appear larger –
hopefully scaring away the enemy
Humans no longer benefit from goose bumps and they are
simply left over from our past when we were not clothed and
needed to scare our own natural enemies. Natural selection
removed the thick hair but left behind the mechanism for
controlling
Video on Evidence & HOMEWORK
 Read text p. 332-339
 Do p. 340 #2, 4-7, 9-12, 16
 Be sure to check out the fossils being passed around