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Lecture 2

PSY354H5 Lecture 2: Sex and Evolution.docx

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Brett Beston

PSY354The Biopsychology of SexLecture 2Sex and EvolutionNATURAL SELECTIONSexual SelectionDarwin conceived of natural selectionCoined the term sexual selection to explain apparent anomaliesoOne individual selecting another for the process of reproduction Darwins Theory of Natural Selection There are variations in traits within the populationoFor a trait to have natural selection it not only has to vary within a population it has to have heritable element within the traitThese variations are heritableoTraits could be passed from one generation to the next If these traits promote survival AND they are passed onto offspring the traits will increase in frequency in a population If these traits are detrimental to survival they will not be passed on and will eventually disappearoAs a result the frequency of this trait will decreaseoNatural selection doesnt necessarily involve a decrease or increase in frequency but it is about a change over timeThe goal for every individual Pass on your own genesoSelfish Gene if natural selection is operating of traits these traits are all derived from an individuals DNA DNA act in a way that ensures multiple copies are passed on to the next generationsNatural Selection in Actions An Example from the GalapagosHome to the medium ground finch Geospiza fortisRecorded each birds morphological characteristics including body and bill sizeRecorded rainfall each year 19751978Recorded number of seeds of each plant speciesoBird with small beaks can easily consume smaller seed whereas birds with larger beaks are able to break through seeds where small birds have no accessIn the 1970s they observed a major drought that caused a decline in seeds and noticed that the small seeds disappeared faster than larger onesThose birds surviving the drought were large birds with large beaksoSmaller birds did not survive because they were unable to consume large seeds and were at a massive disadvantagePSY354The Biopsychology of SexLecture 2Sex and EvolutionWe can see changes that fluctuate over timeBillions of Years for DiversityOver the past 37 billion years species have evolved to what we see todayAfter all that time ts not surprising that there is huge diversity One way in which species are diverse is how they reproduce asexually or sexually Sexual Selection Some structures seem to make organisms less well adapted to their environments EX The Peakcocks TailoEnergetically costly to build and maintainoMakes the peacock much more vulnerable to predatorsNatural selection may have an optimum tail length for survival advantage Perhaps there is an optimum sexual selection for female choiceWe see this curve that is biased towards how long the length can beTwo Components of Sexual Selection Intra Sexual CompetitionoCompetition within one sex for access to members of the opposite sex oWhen we look at inter sexual selection males competing with other males for resources such as food or females Males tend to be good judge of other males abilities Roars are good indicators of how well the other will fightInter sexual CompetitionoCompetition within one sex for access to members of the opposite sexoFemales become very choosey where they will select males with the most unusual characteristics or displays Ie Variations in colouroIn the Lek Polygyny females tend to mate with the same male 90 of the time Females are particularly more choosey and tend to pick the one that stands outBatemans PrincipleFemales should be the choosier sex because eggs are expensive and because a females reproductive success is limited compare to that of a maleoHe said that it starts with the egg itself where it is costly and scares where as sperms are created in billions a day Females need to be choosier because they have more to invest and more to lose if making a bad choice
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