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Lecture 4

Lecture 4 Notes

11 Pages

Biological Sciences
Course Code
Maydianne Andrade

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BIOB51 SEP 23 , 2010 Lecture 4: Evidence for Evolution - Every species is not necessarily endemic  even on these oceanic islands - HIGHER LEVELS OF 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 formed]  More recently derived lineages should be on Hawaii BIOB51 SEP 23 , 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 BIOB51 SEP 23 , 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] BIOB51 SEP 23 , 2010 - It can also result in an increase in the air trapped under the their fur = serves as an insulation layer [so if they’re cold  that keeps them warmer] - It is functionally important in other primates like chimpanzees - For us humans  we get ‘goosebumps’ when it gets cold or when we are excited/scared - So this suggests an interesting underlying physiological similarity [flight/fight situation] or our reaction to cold  that physiological mechanism appears to be conserved with other primates as well - And one of those reactions is muscle contraction [which results in goosbumps] - Most of us relatively hairless  we no longer have hair that is going to erect and give us an insulation layer! - You can see development of these structures [vestigial too!] - Ex: Whales – are mammals! - Where did mammals evolve in terms of their habitat? On land!  That means that whales at some point must have had a terrestrial ancestor. They returned to the sea at some point and evolved into whales after having ancestors that were on land at least according to the evolutionary history of life on earth [that’s the prediction] BIOB51 SEP 23 , 2010 - little pelvic and femur structure = these bones develop from the same embryonic precursors as the pelvic girdle and femur of terrestrial vertebrates that walk on land - In the whale  it just floats and does nothing [connected to nothing] - Clearly reduced in size but it’s there - In the case of whales  we have a really good fossil record of what we believe to be a transition from that original terrestrial ancestor to the point where it was semi-aquatic to the point where it went to the water completely - mammals look more like each other - There are similarities - Pharyngeal pouches: that will develop into gills in fish are present in some form even in humans - Tail: human tail[adults] retracts so that all we have is a tailbone but early in development there is structure that looks very much like a tail and looks very similar to what we see in other organisms especially those more closely related BIOB51 SEP 23 , 2010 - evidence not available to Darwin - Darwin knew nothing about genes - RNA codons that code for particular amino acid are common to every organism that has been discovered so far on Earth - Other codes: work better for less mistakes in mitosis/meiosis - If humans had a...: require high jacking DNA replication mechanisms of our cells [for diseases] - Universal code: makes sense if that code originated in the ancestral forms that were found on Earth and then were inherited by all life forms after that - Looking for common errors can provide some evidence that there was some common source for those errors - flaw seen in humans that is shared with other lineages that we know from the fossil record had a common ancestor - PMP-22 gene
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