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Lecture 2

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Biological Sciences
BIOL 1010
Joy Stacey

Lecture 2 Common Misunderstandings 1. Individuals adapt to their environment - Populations evolve not individuals - Natural selection amplified/diminishes heritable traits - Acquired characteristics are not passed on 2. Traits that maximize individual survival become more common - Behaviours that increase fitness may be detrimental to an individual - Ex. Warning calls in ground squirrels 3. Humans are the pinnacle of evolution - Evolution hasn’t directed evolution toward a certain end point (humans) 4. Complex organisms couldn’t have arisen by chance - Result from evolutionary adaptation to environment - Environmental changes (floods, etc.) that lead to survival of one type of organism at that point can be thought of as chance Incremental Change - Most complex structures evolved this way - Ex. Mollusc eyes: simple pigmented cells evolved into complex eyes 5. There are gaps in the fossil record/missing links - Some transitional fossils are not preserved - Some species leave no fossils - Environmental conditions that form fossils are rare - Transitional fossils were found for whales and their ancestors, birds and dinosaurs Natural Selection • Adaptation for 1 process can conflict with another • Natural selection is the mechanism that always leads to adaptive evolution and production of new species Ex. Sickle cell anemia and malaria Malaria: Parasites live part of their live in blood cells Sickle Cell Anemia: Single change in hemoglobin gene, RBC is sickle shaped - Heterozygous individuals have some sickle cell symptoms but are resistant to malaria - Sickle cell anemia persists in places where malaria is endemic • Natural selection alters populations • Many traits exist along continuum • Selection can favor extremes or an intermediate Stabilizing Selection: Favors intermediate phenotypes Directional Selection: Favors 1 extreme Lecture 2 Disruptive Selection: Both extremes, diversifies population Sexual Dimorphism • Differences between males and females that are not related to reproduction • Can have disadvantages to fitness in some aspects and high fitness in other aspects Sexual Selection - Males with sexually selected traits are chosen by females more - They produce more offspring - Traits passed to offspring - Frequency of the traits increase Other Factors that Contribute to Evolutionary Change • Natural selection, gene flow and genetic drift can interact to produce new species Genetic Drift • Sudden change in genetic makeup of population • Caused by earthquakes, floods, fires, etc • Kills large number of individuals and leaves a small population behind - May not resemble original population (by chance) – bottleneck effect - Displaced population can have different genetic makeup – founder effect (Ex. Genetic disorders in Newfoundland/ isolated areas) Geological Events • Continental drift (Ex. Marsupials in Australia) • 5 major extinctions shown in fossil record - Cretaceous: 65-145 million years ago caused by massive asteroid, climate change, etc. Gene Flow • Individuals moving into and out of populations • Reduces differences between populations and increases variability Species • Biological, morphological,
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