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Web Module - Evolution.pdf

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Christopher Teeter

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Evolution Adaptions – biological traits that help an individual to survive and reproduce in its habitat – they perform in a specific function to make an organism better to the environment – An example of this are eyes, our eyes suited to our environment whereas a raccoon’s eyes are sensitive, their front paws are especially sensitive and can virtually “see” with them – Adaptionists use their label to describe how hypotheses about adaptive function guide their investigations. – You need to break down the problem into sub-tasks in order to look for processes that are capable accomplishing these tasks ( looking for relevant adaptions) Ex. Seeing , how do you detect edges, how do you assess the speed of an object – the adaptive functions are evoked through natural selection Higher Mental Processes – SelectiveAttention – Memory encoding – Memory retrieval – Word recognition These all refer to adaptive functions of mental activity that are needed for the mind to accomplish its jobs. Evolution by Natural Selection – Adaptions are a result of relevant genes in interaction with relevant aspects of the environment – This is all possible because of natural selection Natural Selection : the differential survival and reproduction of organisms as a result of heritable differences between them – This theory was discovered by Darwin and Wallace – It's one of the 4 basic mechanisms of evolution ; the other three are mutation, genetic drift and migration Three Essential Components to Darwin and Wallace's insight 1. Individual Differences : within any population there is variation among inidviduals for any given characteristic 2. Differential Reproduction : these differences affect individual's chances of surviving and reproducing 3. Heritability: this the traits that give differential reproduction a genetic base, which means they are heritable An example of natural selection is a population of fish where there are red and blue fish. The blue fish are camouflaged well in the water, whereas the red fish are more visual. This means that the red fish get eaten more often, leaving the blue fish to reproduce and survive better. Body colour is a heritable trait. Over the next generations, there will be selective transmission of heritable parental traits and the population will mostly be blue. 1. Variation in Traits + 2. Differential Reproduction + Heredity = Selective Transmission Stabilizing Selection : selection against any sort of departure from the species-typical adaptive design – this selection tends to keep traits stable over generations – for example, with the blue fish, over the next few generations, blue would be the most common colour because its adaptive and minimizes risk – However in other cases, when there has been a significant change in the environment, natural selection favours traits that are not typical, and an evolutionary change can be seen, sometimes this change can quite rapid Darwin's Finches – an example of rapid evolutionary change – In 1977 a drought happened on an island inhabited by finches and food was scarce leaving small seeds – the birds that had heavy beaks were able to eat the hard seeds and were able to survive droughts whereas the birds with small beaks died from starvation – Between 1976 and 1978, the average beak size increased from 9.4 mm to 10.2 m – when the drought ended and plants produced smaller seeds, the average beak size returned to pre-drought sizes – Often evolutionists compare and test hypotheses about larger, slower evolutionary change across species Reproductive Success = Fitness – natural selection is also referred to as “survival of fittest”, however natural selection favours the individuals who are best at reproducing – Fitness in biology is used to describe how good a particular genotype is at leaving copies of its genes in the next generation.As a result, the fittest individual is not always the smartest, biggest or fastest – Evolutionary biologists like to define evolution as a change in gene frequencies over generations Sexual Selection (2 theory by Darwin) – the component of natural selection that acts on traits that influence an organisms's ability to obtain a mate – in organisms that reproduce sexually, there is often a competition for mates, and natural selection acts on mate-finding and reproductive behaviours known as sexual selection – some evolved traits like the peacock tail increase mortality and are actually selected against in that context Peacock Tail – energetically expensive to produce (he will shed his tail at the end of the breeding season and grow a new tail the next year) – more conspicuous to predators – harder to get away from predators – increases risk of dying Two subtypes of Sexual Selection Sexually Selected Traits – both traits have negative effect on survival – for the elk: antlers are used in combat – for the peacock: tail-feathers are used in courtship ( has a negative effect but big positive effect on the male's chance of reproducing) – the selective force in the evolution of peacock's tail was female choice, whereas in the case of the elk, the selective force was success in combat with other males – Two distinct ways of getting more access to mates than your rival 1. being more attractive and being chosen by the opposite se 2. to beat up your rivals (if you can eliminate the other competition then you are the only choice left for mating) – if an anatomical trait differs between sexes, thats a clue that it may be a sexually selected trait – if the sex difference only exists during breeding season or is exaggerated at that time of the year, thats another clue Species-Typical Behaviour & The ComparativeApproach – behaviour – like anatomy – is an evolved characteristic of a given species was the starting point for modern science of animal behaviour – 3 different birds that look similar can be recognized at a glance by avid bird watchers just by watching their behaviour, vocalizations, dietary and habitat preferences – Example : sanderlings race out after receding waves and furiously peck at tiny insects on the wet sand, then race back towards shore before the next wave, with their little legs spinning like wind-up toys. Species- Typical Behaviour or Species- characteristic behaviour – physical form ( typography) – habitat preference (where the go, and what they choose to eat) – group size (do they prefer to be alone or in a group, do they fly by day or night) – social system (do they mate monogamously or polygamously, who raises the kids) – Behaviour genetics experiment – keep animals in captivity and selectively breed those who are more or least aggresive or whatever trait you like, and you can change the animal's typical behaviour in a few generations – in order to complete your experiment before you retire or die, then you need to use animals with short generation times; the fruit fly is popular for this reason Social Behaviours – Examples of where individuals appear to behave altruistically: helping others at a cost to themselves 1. Honeybees – never reproduce, they spend their lives helping to raise eggs laid by the Queen Bee. Most die defending their colonies from predators 2. Beldings ground squirrels – individuals give alarm calls to warn that a predator is in the area, giving everyone a chance to run. But they risk themselves by being the alarm call and alerting the predator of their location. 3. Humans – you spend a lot of your time co-operating and helping friends, family and strangers “Selfish gene” – the gene that will get replicated more often because they contribute to the gene fitness .
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