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Lecture 2

Lecture 2 Notes

13 Pages

Biological Sciences
Course Code
Maydianne Andrade

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BIOB51 TH SEP 16 , 2010 Lecture 2: Introduction to Darwinian Evolution 1) Big questions in biology - These questions arise from our observations about the natural world - The diversity of different life forms on earth - And the fact that within that diversity there is clusters of similarity - So, similarity in diversity ! - “So they are diverse within a certain level of similarity that is different from other organisms” – prof  ADAPTATION [= “GOOD FIT”] – Organisms tend to be very well suited to their environments. [In some cases the environment is static ( land), in other cases – it‟s changing (water) ] - They can do what they need to do – to survive & reproduce in those environments. Even if those environments are incredibly challenging to live in. e.g. Crypsis - the ability of an organism to avoid observation or detection by other organisms. [In sophisticated ways] for example – a dead-leaf butterfly (Kalima inchos) & flatfish. - SO these are the types of observations that led ppl to ask questions about how we could understand biodiversity So big questions in biology:  How did life arise?  What accounts for the diversity of species?  Why are organisms so well suited to their environments (How do we explain adaptation )?  BEFORE DARWIN‟S TIME: - The dominant idea about explaining life on earth [that is the existence of life in the first place, biodiversity & how it was organized as well as adaption – was the idea of SPECIAL CREATION] BIOB51 SEP 16 , 2010 - But evidence was accumulating that maybe „special creation‟ wasn‟t the best explanation of biodiversity! - Evidence suggests that organisms had in fact changed over time. And that all the lineages were not necessarily the same as ones that existed in the past. Not only had some changed but some had also gone extinct. - Extinction was not part of the special creation idea! - Environment of the earth wasn‟t static since the creation of earth – it had also changed over time!  The reason why changes in the environment overtime were important to thinking about biodiversity is that „special creation‟ suggested that organisms had been built/created in the beginning to fit their environments (thus adaptation). So, they were created to be adapted to their environment and then had not changed over time.  So how could that be reconciled to the idea that environment‟s itself had changed over time? So we have evidence to suggest that environment has changed over time – so how can organisms that haven‟t ever changed since their creation be adapted to their current environment?  Therefore, this insight from geology [changing environment of Earth] was important for biologists!  So accumulation of more and more evidence that there was suggestions that species were more or less related to each other as opposed to all having being created independently – there was this clustering of similarity! – not just in terms of the way they looked but also in terms of how they developed. BIOB51 TH SEP 16 , 2010  So basically relatedness of species as opposed to independent creation! - This became more and more of a prominent thought among biologists.  THE CLASSIFICATION SYSTEM AROSE BEFORE DARWIN‟S TIME.  This system essentially recognizes the fact that characteristics of organisms shows natural clustering.  This clustering was recognized in classification schemes even though at that time when they developed the classification scheme – they weren‟t yet talking about evolution!  THE NEW IDEA.  So, the new idea that appeared even before Darwin was that in fact species had changed over time and that species derive from common ancestors as a result of divergence of lineages over time.  Note: think of lineage as line of inheritance  So in this case – it is the diversity we see now requires that the earth is very ancient – b/c it has to have been a lot of time for these organisms to have diversified from one or few original ancestors.  So this idea of evolution is actually quite an old idea and rests on evidence from wide range of diff. Sources. BIOB51 TH SEP 16 , 2010  NOT THE BEST EXPLANATION: - So, looking at all this evidence - it suggested to many people at the time that the historical „special creation‟ was not the best explanation for existence of life and diversity on Earth. -BUT! - This evidence – these early ideas about evolution could still NOT explain adaptation  They knew that species had changed over time -> They knew that environment‟s had changed But they could NOT explain why it was that organisms were than adapted to their current environments!  EARLY DEFINITION OF EVOLUTION (IDEA OF CHANGE) - Now it might not seem surprising but it was a radical idea at that time - This puts the idea of evolution as a possible central idea that would explain these big questions in biology - but again at the time they could not explain adaption – so this is where Darwin came in! - Darwin was not the first to propose the theory of evolution – many famous ppl that did this - including his own grandfather. - In addition, Lamarck who proposed the theory of evolution and a mechanism that has since been widely discredited - that is the inheritance of acquired characteristics. 2) What was Darwin‟s key contribution to evolutionary biology? - Darwin proposed a plausible mechanism - A mechanism by which evolution could work - And a mechanism that could lead to adaptation - Thus making it plausible that evolution could explain all of the big questions in biology. BIOB51 TH SEP 16 , 2010 - So his book – “On the Origin of Species by Means of Natural Selection” - So it‟s the „Means of Natural Selection‟ that makes his contribution so central to evolutionary theory.  SO DARWIN IS CONSIDERED THE PARENT OF MODERN EVOLUTIONARY THEORY - On the slides - So, he showed that evolution by natural selection had occurred!  EVOLUTION – PROPOSED BY CHARLES DARWIN - NO supernatural intervention required to explain adaptation!  Descent with modification - Descent = you descent from your ancestors - Modification = b/c there is changes along the way that eventually leads to splitting of lineages into new types of organisms [So this is very diff. to the ideas that were dominant before him] BIOB51 TH SEP 16 , 2010 3) Evolution by natural selection [KNOW THIS ONE!*ON MIDTERM/FINAL] Postulates: 1) Even zebra‟s that look all the same to us are different from each other! ( stripe patterns) This includes flowers and other organisms. Ex: face patterns on wasps – diff. from individual to individual. So there can be differences in shape, colour, and size! 2) Some of the variations passed on – offspring tend to look like parents. So you get traits from your parents/ancestors. 3) Deduction = recognizing the reproductive potential of individuals and then calculating how many of them we should see around us if all of them or most of them were surviving and reproducing themselves [Darwin talked about this] –on slides Observation = we also know the processes that lead to differences in survival. Because of these BIOLOGICAL FACTORS, some individuals don‟t get enough food or the shelter they need – or they are just outright killed by other individuals. There are also PHYSICAL FACTORS that can kill individuals – like clim
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