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Evolution I and II .pdf

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McMaster University
Joe Kim

Psych 1XX3 – Evolution I and II – Jan 11, 2010 Def’n of Adaptation: Biological traits or characteristics that help an individual survive and reproduce in its habitat. Adaptations are always “for” something, they perform specific functions that make an organism better suited to its environment. Examples: Eyes enable us to recognize and respond effectively to things, and raccoons have good night vision, their front paws are so sensitive they can virtually see with them to scavenge for food. To understand how we manage to see, hear, respond to stimuli  scientists break these problems down into sub-tasks: how do you detect edges? How do you assess the speed of an object or perceive a threat? Then… you can look for processes that are capable of those tasks (relevant adaptations). Scientists categorized as “adaptationists” use this label to describe how hypotheses about adaptive function guide their investigations. What about “higher” mental processes… selective attention, memory encoding, memory retrieval, etc?  They refer to the adaptive functions of mental activity. The adaptive functions evolved like all other adaptations – through natural selection. Adaptations emerge in development as a result of activation of relevant genes in interaction with relevant aspects of the environment. Def’n of Natural Selection: Differential survival and reproduction of organisms as a result of the heritable differences between them. Three Essential Components: 1. Individual differences: There is variation among individuals for any given characteristic. 2. Differential Reproduction: This variation affects chances of survival; some individuals will produce more offspring than others 3. Heritability: The offspring of successful reproducers will resemble their parents. Selective Transmission: Occurs over successive generations when one trait is more favourable than another. Eventually the entire population contains only the most favoured trait. Stabilizing Selection: Selection against any sort of departure from the species typical adaptive design. Example on next page. The example above was not permanent: After the drought was over and plants produced smaller seeds again, the avg beak depth of the finches returned to pre drought sizes. However… sometimes changes that arise thru natural selection are more permanent and form a potential foundation for diversification of related species. Key point: What natural selection favours is not simply those individuals who are best at surviving. It’s those who are best at reproducing. Def’n of Darwinian Fitness: Average reproductive success of a genotype relative to alternative genotypes. (Note that fitness has nothing to do w/ biggest, strongest, fastest I.E. physical fitness) Def’n of Evolution: A change in gene frequency over generations. Def’n of Sexual Selection: The component of natural selection that acts on traits that influences an organism’s ability to obtain a mate. Example 1: Peacock’s tail. The tail is no help with respect to physical survival  it’s energetically expensive, and makes it harder for him to escape predators, however, Darwinian fitness isn’t a ratter of survival, and it’s a matter of reproduction. The tail increases his chances of mating.  this trait elevates mortality, but can still evolve under the countervailing pressure of sexual selection.. female mating preferences in this case. Example 2: Stags (male deer) have horns to fight for mating purposes. However, carrying around all this weaponry makes them more vulnerable to predators than females because they don’t have as much stamina for running and are more likely to get stuck in the snow. Similar to the peacocks, the trait has a negative effect on survival, but perists anyways because it has a big positive effect on the male’s chance of mating. Differences: Peacocks don’t use tails to fight with. Females are dazzled by the male’s tail. However, female elk do not care about the size/appearance of the stag’s antlers. Therefore, there are two different ways of getting more access to mates than your rivals: (1) Being chosen by the opposite sex (attractiveness) and (2) beating up on your rivals in mating combat. The evolution of the peacock was by female choice, where as the evolution in the case of the stag was success in combat. Note: It has been shown experimentally that female peacocks prefer more eyespots and more symmetry. They may have these preferences because they want to pick out mals with the greatest resistance to locally prevalent diseases, so a female may be making sure that the father of her children gives them the best available genes. Species-Typical Behaviour and the Comparative Approach  Behaviours are an evolved characteristic of a given species  Test hypotheses about adaptive functions Example: 3 different types of sandpipers: Sanderling, Semipalmated and Dunlin  each behaviour is different (I.E. in how they forage for food) Behaviour Genetics experiments: you can keep animals in captivity and breed those who are most or least aggressive, those who like water/hate water, etc and change the animal’s typical behaviour in a few generations. Evolution II: Intro to Social Behaviours Organisms evolved to maximize their fitness and reproductive success  however, there are examples in humans/social animals where individuals behave altruistically (helping others at the cost to themselves) Example: Almost all honey bees don’t reproduce, but help the queen raise eggs and die defending predators. Example: Squirrels frequently give alarm calls to warn others that there is a predator in area, but then draw attention to themselves are alerting themselves to the predator Example: Humans aren’t selfish; they help others Concept of Selfish Gene: How evolution (working at the level of genes) favours those genes that contribute to an individual’s fitness and will consequently get replicated more often, increasing in frequency each generation Table of social behaviours on next page  if someone does something that helps himself and others, the behaviour is a cooperative one, etc.  Example: You have 6 players on team, but Billy isn’t very good at playing. You can invest time and resources to teach Billy to play better. On the surfact it looks like you’re unselfishly doing extra work, but it may pay off (I.E. team may win more games).  In language of evolution, increasing the fitness of others can sometimes improve your own fitness prospects. Group Selection: Common misunderstanding (Key point): adaptations aren’t for the food of the group/species, they are for the good of the gene. (I.E. in the previous example, helping Billy do better isn’t a good enough reason evolutionarily… what matters is that the increase in group success translates into better success for the metaphorical helping gene) Example: Geese forage for food in groups  this is because multiple individuals are looking around for food, so if you happen to be the lucky one to find the food, some may be taken from you, but more often you’re taking from others. HOWEVER, there is another reason why geese do this. While some birds forage, others are vigilant in order to prevent being surprise attacked by predators. Image on following page: As the flock size increases, the number of times a each bird looks up (being vigilant) decreases. Does this mean larger flocks are more susceptible to attack? No. The number of head jerks for the ENTIRE FLOCK increases. This means, even thought each individual is looking up less, the group as a while is being more vigilant than any one individual alone. Key point: Can selection be good fo
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