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BIOB51: Evolutionary Biology - Lectures 2 & 3 Review
BIOB51: Evolutionary Biology - Lectures 2 & 3 Review with Questions
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LECTURE 2 TOPICS❖ Why is it often difficult to conceptualize biological evolution?
➢ Mechanisms within evolution are challenging to describe
➢ There are issues with scale and the concept of time
➢ Difficulty demonstrating and observing “evolution” in a teaching lab
❖ What is the difference between a theory and a fact?
➢ Misconception → “Evolution is not a theory, it's not a FACT”
■ “Fact” → information that can be used as evidence
■ Theory → well-established, well-supported, well-documented explanation
for our observations and is supported by facts
➢ A theory is an explanation of facts
❖ What is the relationship between theory and law?
➢ Law → a description
➢ Theory → explains the WHY
■ E.g. Law of gravity is a description and it does not explain the why,
whereas Newton's Theory of Gravity, Einstein’s Theory of Relativity
explains the WHY (theory)
➢ Evolution → also is something that is true,
observable and testable
■ E.g Speciation is a description
(law): when a group within a species
separates from other members of its
species (common ancestor) and
develops its own unique
characteristics
● A theory then will explain
this law → as to WHY
speciation occurs
❖ Why is it essential that we have a grasp on the concept of time, in an
evolutionary sense?
➢ Scale and the concept of time
■ Several million years may seem like a long time to us BUT in
evolutionary terms, it is considered recent because even after
several million years of divergence, our DNA is still 99%
identical
, ➢ Demonstrating Evolution
■ Showing the effect of light on plants is something that can
be done in the lab even now → Anywhere in the world
■ Proving that DNA is the heritable material in our body is
also something that can be demonstrated in a lab setting
➢ BUT, You can’t “do” evolution again
■ You can’t demonstrate evolution
■ How do you show that a whale evolved from a
camel
➢ All of this “stuff” (change) didn't happen overnight → took a very very long time
■ Biological evolution → is a process by which populations of organism
change over time
❖ How does an understanding of evolution inform us about all aspects of life and the
interconnectivity of life?
➢ Every organism that lives today on Earth are all a PRODUCT of evolution
■ By understanding evolution, we can understand
● WHY is the natural world the way it is today?
● The similarities and differences among and between species
● The geographical distribution of species
● The adaptation and weaknesses of living things
➢ Studying evolution can help us in many ways (E.g.)
■ Finding new ways to fight off deadly viruses and bacteria that make us
sick
■ Allows us to have a better understanding of how insects become resistant
to pesticides
■ We can understand the consequences of human impact on the planet
● Pollution
● Climate change
● Invasive species
■ We can compare today's extinctions to the past → which can help us
predict and think about new strategies to combat the current wave of
extinctions
,❖ Why do we know that whales are mammals? We discussed several features and
examples.
➢ Whales share many synapomorphies with mammals
■ Synapomorphies → derived form of a trait that is shared by a group of
related species, a trait that evolved in the immediate common ancestor of
the group and was inherited by ALL its descendants
● E.g Synapomorphies in whales and mammals
◆ Mammary glands
◆ Three middle ear bones
◆ Hair (in developing embryos)
❖ What is Pakicetus and how does it fit within the phylogeny of
cetaceans?
➢ Pakicetus (“whale of Pakistan”) → ancestors of whales
■ Was the first terrestrial cetacean (Latin: “large sea
creature” - collective noun used to describe all 90
species of whale, dolphins and porpoises) ever
discovered
■ Fossils showed → a whale that spent at least some time on land
➢ Pakicetus shared similarities with modern relative (E.g dolphins and whales)
Dorudon: they show strong resemblance to
teeth of some extinct land mammals
(pakicetus)
, Pakicitus had cetaceans synapomorphies
● Fragments of skull revealed Pakicetus
to have cetacean-like involucrum
(thick lip of dense bone that forms the
inner wall of the ectotympanic found
in mammals)
● Bone found in the ear: Both have the
same bone structure links the
Pakicetus to the dolphin
Talus = Astragalus → “ankle bone” →
synapomorphy
Shape of the astragalus bone is more
important in this case:
● The bone is more similar to the bone
of ungulates (having hoofs and
specifically even-toed).
●
● Thus revealing that the pakicetus
could have been more closely
connected to ungulates rather than
canines
● Transitional fossils reveal that
pakicetus are linked to land
mammals
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