Why Sex?ANTH 1031. Benefit of sexual reproduction is that it increases genetic variability. Sex generates variability among offspring. And when you take that away from a sexual reproducer by inbreeding them, cloning them, you've lost the very benefit of sex. It's that generation of an immense amount of diversity, that diversity of your offspring that provides challenges to everything around it: challenges to the parasites, challenges to the viruses, challenges to your competitors. Sexual process - the variation and wonderful diversity it creates. The easiest way for an organism to reproduce is simply to divide asexually--to make a copy of it. An organism that reproduces sexually, however, must divert precious energy into making sperm or egg cells; in the process, gene combinations that were quite useful beforehand are sometimes destroyed through "recombination." Then the organism must find a member of the opposite sex and mate with it successfully. From an evolutionary perspective, sex incurs considerable costs that mustbe offset by advantages to the organism. 2. Male (Quantity): Organisms with reproductive cells like that are called males. Males produce sperm by the millions, with so many potential offspring it doesn't pay to be fussy about eggs. A better strategy is to try to fertilize every egg you canFemale (Quality): Their goal is to find organisms with a different specialty--providing the nutrients life requires. Females make only a limited number of them (Eggs are more complex than sperm and take a larger investment of energy). Females engage in choice, while males engage in competition. Male competition may take the form of fightingBird in Panama: survival of chicks is so uncertain it's led to an amazing gender role reversal.Male: sex competes for matesFemale: invests in the young3. Caring young offspring: The young have to survive long enough to have their own offspring. Sometimes that requires paying as much attention to behavioral traits as to physical ones. For some species, the chances of offspring surviving increase if a female chooses a mate who'll stick around over the one with the best genes.4. Songbird : returning from migration sometimes has to settle for a fairly low-quality male in comparison with her neighbors. The female is now torn between a desire to have a faithful mate who will help her raise her young, and a desire to have her chicks sired by a male of higher genetic quality. Cheating, at least for certain female songbirds, gives their chicks better genes, and therefore a better chance of surviving until they can reproduce. Behavior of males and females depends on which sex competes for mates and which invests in the young. Yet the males of these Panamanian birds still produce sperm, and the females still lay eggs. Bird in Panama: survival of chicks is so uncertain it's led to an amazing gender role reversal. So many chicks are lost to crocodiles that females leave their eggs for the males to raise, and go off to reproduce again. Now it's the females who care more about quantity than quality. Now it's the females who fight over mates. Over time, they've taken on traditionally male characteristics. The females of this species are aggressively territorial, and try to attract "harems" of four or five males.5. Chimpanzees and bonobos look alike, live in similar environments, and eat similar food. Chimpanzees are very pugnacious, however, while bonobos are essentially peaceful. Bonobos are predisposed to make love, not war. bonobos having heterosexual and homosexual intercourse. Bonobo females are "able to form alliances with each other and cooperatively dominate males. And this changes the whole balance of power and the whole social dynamicin the group, and makes it radically different from chimpanzees. Feeding ecology is responsible for this dramatic difference in sexual behavior. Bonobos live in forests where they can forage for food on the ground. Although there are chimpanzees that live in similar forests, those forests are also occupied by gorillas. The gorillas eat the food on the ground, leaving the chimpanzees dependent on fruit trees. So female chimpanzees have to forage intermittently and alone, without the opportunities for social interactions enjoyed by female bonobos. There was food available on the ground appears to have been the force that drove the evolution of bonobos.6. Regardless of the culture in which we grow up, we all tend to respond the same way to a surprising variety ofthings. Most of us find spiders unpleasant, certain body type’s sexy and particular smells disgusting. Choosing amate with different immune genes gives offspring a greater protection against viruses, parasites, and otherpathogens. Facial beauty is simply a collection of subconscious biological cues that let us know whether a potentialmate is genetically desirable. When choosing a mate, we still notice beauty, but what really counts is how someonethinks, feels and acts. All of these are products of the brain. The human brain is the most complex system in theknown universe. It's wildly in excess of what it seems like we would need to survive on the plains of Africa. In fact,the human brain seems so excessive that a lot of people who believe in evolution applied to plants and animals havereal trouble imagining how natural selection produced the human