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Lecture 4

BIOB51H3 Lecture Notes - Lecture 4: Dna Replication, Myelin, Intron

Biological Sciences
Course Code
Maydianne Andrade

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SEP 23rd, 2010
Lecture 4: Evidence for Evolution
- Every species is not necessarily
endemic even on these oceanic islands
ENDEMISM among those organisms that
are less likely to disperse
- So the proportion of endemic
species among organisms that have very
low dispersal ability should be HIGHER
than those that can disperse more easily
- Nihau = oldest island [has begun to erode and
is smaller]
- So if you think of animals/plants landing on an
island and then evolving there but also the
probability of moving off the island [which is
possible when these islands are so close together]
There is prediction about what you would find
here based on the order in which they would land on
the islands:
So the idea is that the more ancient lineages
would probably would have landed on the oldest
island [formed further in the past]
And if there are migration events
they would happen from one island
to the next to the next! [in the
temporal order in which they
More recently derived lineages
should be on Hawaii

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SEP 23rd, 2010
- So dispersal ability and barriers to dispersal
do seem to shape the patterns of distribution
we see on Earth
- Evidence for this had accumulated way
before Darwin’s time
- Darwin just proposed that it was best
understood in light of his theory [it wasn’t his
idea or data though]
- ‘Likeness’ or similarities of animals
and plants have been recognized for
centuries = HOMOLOGY
- Embryonic precursors: what we can
now do is that we can locate primordial
cells in an embryo and then watch and see
where they move during development and
what they turn into

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SEP 23rd, 2010
- These colour-coded bones start from the same embryonic precursor cells in those
original embryos
- Get this information from the fossil record
- You can also see it by looking at development
- This is the idea of homology!
- Often reduced in size [not always the case]
Found in one set of organisms in this reduced,
functionless form and are found in organisms that we
now recognize to be related to them but are functional in those organisms!
- In primates: when they are excited/frightened that muscle contracts and their hair
fluffs up [that’s very important in aggressive/agonistic interactions]
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