Evolution of Sex and Love

Evolution of Sex - Evolution of Love Have you ever been in love A Yes B No C Maybe D I don't know 30 0 1 0 2 0 3 0 4 Which word best summarizes

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Unformatted text preview: Evolution of Love Have you ever been in love? A) Yes B) No C) Maybe D) I don't know 30 0% 1 0% 2 0% 3 0% 4 Which word best summarizes your view of love? 1) 2) 3) 4) 5) 6) 7) 8) 9) ardor Women answer first. amour infatuation crush passion tender feelings affection care giving lust 0 % 0 % 0 % 0 % 0 % 0 % 0 % 30 0 % 0 % 1 2 3 4 5 6 7 8 9 Which word best summarizes your view of love? 1) 2) 3) 4) 5) 6) 7) 8) 9) ardor Now, men answer amour infatuation crush passion tender feelings affection care giving lust 0 % 0 % 0 % 0 % 0 % 0 % 30 0 % 0 % 0 % 1 2 3 4 5 6 7 8 9 What is love? Webster's dictionary 1) Strong affection for another arising out of kinship or personal ties 2) Attraction based upon sexual desires What is love? Roget's Thesaurus Ardor, amour, infatuation, crush, passion, tender feelings, affection. What is love? Love: Strong emotional bond Affection: Personal attachment Is care given or received? Do individuals spend time together? When do we use the word love? What is the selective advantage of love? Self love--health & survival 2) Sexual love--reproduction But why not asexual reproduction? 1) Lots of organisms do it? Asexual reproduction Binary fission Asexual reproduction Budding e.g. hydra Asexual reproduction Vegetative reproduction grass aspen Some lizard species have only one sex-- females. They reproduce parthenogenetically --that is, females produce eggs that spontaneously start development without sperm being involved at all. They are completely asexual. Parthenogenesis Asexual reproduction Some species have it both ways: they reproduce both sexually and asexually. Queen bees when they produce females (workers) release sperm out of a storage sac and fertilize the egg in the normal way, but when they want to produce males (drones), they hold the sperm back and the eggs develop by parthenogenesis. Water flea (Daphnia) populations seem to switch from asexual to sexual depending on environmental conditions. And some species of fish actually switch from being one sex to the other depending on which gender is in short supply. How did sex evolve? Eukaryotes evolve true mitosis & meiosis Sex is dependent on meiosis Fertilization doubles the number of chromosomes & meiosis cuts it in half And why only two sexes? Why Did Sex Evolve? It doesn't have to be that way. Some fungi have dozens of sexes, Asexual vs. Sexual Reproduction Questions Propose an hypothesis to explain why sexual reproduction has evolved. (At least 20 have been suggested!) Can you suggest any way to test your favorite hypothesis? "In a world without sex there would be no males and females. No flowers, no insects specialized in pollinating them, no extravagant colour and form like the peacock's tail; and much animal behaviour would not exist." --Rolf Hoekstra The German biologist August Weismann proposed an answer to the question of "Why sex?" He asserted that sex increases genetic variation. When two different individuals mate by joining their gametes together, they produce a brand new genetic mixture and this promotes evolutionary adaptation. BUT: 1) Mixing of the genes tends to break up favorable combinations. Why break up a good thing? 2) Asexual reproduction is twice as efficient as sexual reproduction at sending one's genes into the next generation. Every time a sexual mother produces a child, that child only has onehalf of the mother's genes; the other half is from dad. But an asexual mother reproducing parthenogenetically would give her child the complete set. In asexual populations every individual would be capable of reproduction (i.e., be a female). Such populations should rapidly outreproduce a sexual population. This has been called the "Intrinsic Cost of Sex." It seems clearly disadvantageous for individuals to reproduce sexually! Yet sex has evolved and seems here to stay. Perhaps sexual reproduction is advantageous in a harsh environment. Question Can you design a way to test the hypothesis? There is a snail that lives in New Zealand lakes that has both asexual and sexual individuals. Dr. Curtis Lively (currently at Indiana University) and his colleagues decided that the snails could be used to test the hypothesis because there were many ponds that had parasites and others that didn't. This is what they found: In ponds where there was a high degree of parasitism there was a much higher percentage (2.5 times more) of sexually reproducing individuals. Which of the hypotheses about the ponds is most consistent with modern evolutionary principles? 1) The ecosystem needs to have a predominance of sexual species in order to have the variation to evolve. 2) Asexual varieties are inherently weaker than sexual varieties when faced with parasitism 3) Sexual varieties are more variable and thus have some individuals that are more likely to survive under the conditions of parasitism. 4) Asexual varieties are more likely to overbreed because of their faster reproductive rate than sexual varieties and become extinct. 45 0% 1 0% 2 0% 3 0% 4 Experiment A team of scientists at the Imperial College London tackled the problem and published their results in Nature magazine (March 25, 2005). They used yeasts, because they can reproduce both sexually and asexually. Yeasts normally reproduce asexually, but when they are stressed (starved, high temperatures, etc.) they will reproduce sexually. The scientists did not want this switching to occur. So they genetically manipulated one asexual strain. They deleted the two genes (SPO11 and SPO13) required for normal meiosis, so that sexual reproduction was impossible. Now they had two pure strains--asexual and sexual. The Imperial College team decided to compare the reproductive rate of the asexual vs. the sexual yeasts in two different conditions: One in a benign environment raised at normal temperature and the other in a harsh environment raised at a high temperature with a higher osmotic pressure. Both groups had plenty of nutrients. Question On a graph plot the results you would expect if Weismann's hypothesis were correct. Recall Weismann hypothesized that sex increases genetic variation. First, plot a graph over time of how you would expect the asexual yeasts to do in benign (good) conditions. (Hint: Would fitness change over time?). And plot how the sexual yeasts would do time?). And plot how the sexual yeasts would do in a benign environment. Now suppose this is the plot of the asexual population in a harsh environment If LINE B represents the asexual data, which line represents the sexual data if Weismann's hypothesis is correct? 0% 1 0% 2 0% 3 0% 4 0% 5 30 Here are the real data Which statement best represents the conclusion you should make from the last experiment? A) We have proven Weismann's hypothesis B) We have proven the null hypothesis C) Sexual reproduction is superior to asexual reproduction D) Weismann's hypothesis is supported E) Benign environments exert little selective pressure on yeast cells 30 0% 1 0% 2 0% 3 0% 4 0% 5 2) Sexual love Cont.' Incest Taboos (counteract inbreeding) Homosexuality (Why isn't this behavior eliminated via selection?) 3) Love between parents & children Parental love (care) increases survival of genes Children love parents Behaviors that encourage parental care increase their survival. Parents give protection, food, etc. Parents might help raise your grandchildren Parents share valuable information with children 4) Sibling Love Kin selection--your siblings carry half of the same genes you carry. Inclusive fitness Lion brothers Reciprocal altruism in social organisms 5) Love between unrelated individuals that live a long time and have good memories. "You scratch my back & I'll scratch yours" Coalitions form Is love genetic or learned? i.e. Are the specific behavior patterns that we associate with love inherited or learned? A) B) C) D) E) Almost all genetic Maybe 80% genetic 50% genetic & 50% learned Maybe 20% genetic & 80% learned Almost all learned 0% 0% 0% 0% 30 0% How should we attack this question? Questions to answer: Are there selective advantages to "love?" Do closely related species show the same behavior patterns? Do almost all members of the same species show similar behavior patterns? Evidence Breeding experiments Brain studies Comparative studies of behavior Hormone studies Chemical studies Studies of comparative behavior among humans Appeasement gestures Smiling Pupil dilation Gift giving Soft sounds & nice words Brain Studies Hypothalamus seems to be a key site for pleasurable responses Rat studies Hormone Studies Progesterone/estrogen Oxytocin Endorphins From the posterior pituitary. Oxytocin 1) Simulates milk let down 2) Stimulates uterine contraction 3) Stimulates pair bonding--with sexual partner in prairie voles 4) Stimulates maternal behavior 5) Promotes trust and generosity 6) Drug MDMA ("Ecstasy") increases feeling of love, empathy, and connection to others stimulates oxytocin activity. 1) Amphetamines, cocaine = "thrill of the Chemical Studies moment," energized, excited 2) Narcotics= "walking on air," happy, euphoric, optimistic 3) Valium, librium= calm, peaceful, relaxed 4) LSD, mescaline, psilocybin = awestruck, mystical, spiritual, "feeling of the intimate moment" When did love evolve? "Self love" has a long history--3.5 BYA "Sexual love" started with eukaryotes ~2 BYA "Parental love" in the vertebrates > 350 MYA Some fish, some amphibians, s. reptiles; all birds, all mammals care for young. "Sibling love" s. vertebrates, s. insects ~90 MYA "Love of God" > 100,000 ? when Neanderthals were burying their dead What is love then but a set of behaviors when 2 or more organisms interact affectionately, with behaviors, which on the average, promote survival of their own genes. The organisms do not have to be aware of their "feelings" as long as their behavior leads to improved survival of their genes. "Love" is partly a response to a set of biochemical actions in the brain & the result of evolution ...
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This note was uploaded on 12/09/2009 for the course BIO 200 taught by Professor Herreid during the Spring '07 term at SUNY Buffalo.

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