The sexual deformity causes males and females of the same species differ not only for the reproductive system for secondary sexual traits. In addition to physical traits you notice different behaviors. Darwin suggested that natural selection operates alongside the sexual selection.
At first glance the presence of both sexes seem disadvantageous in that: an individual would parthenogenetic offspring with 100% of its genes, and after a few generations would count more descendants.
sexed species in asexual contend that an environmental niche show that sexual reproduction with recombination allows individuals to procreate with greater genetic variation and therefore adaptability.
Reproduction assesuale is suitable for stable environmental conditions.
L ' anisogamia is the difference between male and female gametes sex. In most species the eggs are larger and a few sperm and many children.
Sexual selection favors traits in males that increase their mating success. In
intra-sexual selection favored males will be stronger in competition with other males. In
inter-sexual selection will be favored males that have characteristics favored by females.
The section that highlights the sexual selection is then balanced by natural selection, otherwise one would see a 10m high peacocks with tails or horns from deer with 100kg,
In the female sexual selection favors the selectivity , in fact a male who makes a mistake in the reproduction does not have serious consequences, a female hand, has a risk and a higher cost. The selectivity is expressed by choosing males with superior genotype, with parental skills and resources.
In humans it was found that in different cultures that attract female characteristics are inherent in the male and female physical attractiveness instead is the availability status and economic men (Buss, 1989).
A final aspect of sexual selection and sperm competition, some species have developed techniques to prevent the sperm of other males to fertilize the female arrivals who are courting.
sexual conflicts
Because dell'anisogamia and sexual selection often the interests of the two sexes are different, so that sexual selection will favor sexual traits unfavorable for the other sex. This situation triggers a sexual conflict.
A very common conflict between species is that concerning the parental care, in this case in some species the female must implement strategies to ensure that the male participants rearing of offspring without it having another female.
L ' infanticide in the lion and the mouse is a strategy that implements the new male to ensure that females stop feeding and enter into inspiration for the time domain is limited, and after winning the competition entail a risk to wait. The mouse comes to kill the male offspring born the following week. The
counterstrategies are avoid abandoning the demand for a long and persistent courtship to prevent infanticide lionesses involved in the struggles of male residents. The female mouse embryos reabsorbed into contact with the odor of new male "Bruce effect."
addition to behavioral strategies, we are witness to a chemical warfare. Some secreted substances in the ejaculate work by inhibiting the anti-aphrodisiac female libido, others act as a spermicide after mating.
in the male fruit flies produces a toxin that shortens the life of Acp female.
In our species, some compounds inhibit the immunological function in sperm female apparatus, which reduces the supply of sperm. There are of neuro-modulators, anti-aphrodisiacs.
prostate protein PSA helps move the sperm into the uterus, but also causes prostate cancer. The incidence of this is 60 years.
In some species, males have to endure. In the case of the female mantis, and some spiders, bigger, devouring the male just after fertilization. We are witnessing infidelity in monogamous pair of certain birds, then the token male, the female for days required for egg laying ( mate guarding ) In other bird species only one parent is sufficient that the female attempts to cheat male on the fact that he laid in his nest, but if the male finds the female rimmarrà to care for the eggs, otherwise it belongs to my son.
Occasionally males devote themselves in a sexual obsession ( sexual harassment) that in many cases leads the female to give up to reduce costs.
Altruism and Cooperation
Topics include overall fitness and kin selection, reciprocal altruism and cooperation.
Altruism: an individual behavior that increases the fitness of others at the expense of their own.
Altruism is apparently in contradiction with the theory of natural selection, but is explained if we introduce the concept of total fitness which is the sum of its fitness (direct fitness) and fitness indirect (genes shared by relatives) , Hamilton (1964).
The mechanism that allows the evolution of altruistic behavior is the kin selection (kin selection ), Hamilton has shown that the condition for which an altruistic allele is inherited is explained by the inequality:
C \u0026lt;B * r => Cost \u0026lt;Benefit * The coefficient of kinship
kin recognition is the recognition of individual indiviui related. The easiest answer to the rule "if it is grown in your own nest then it is your brother." Another mechanism underlying the kin recognition is the phenotypic comparison, for example, by comparing their major histocompatibility complex (MHC), which is expressed by the smell, with another individual. Humans are recognized physical traits, eg. DeBruin (2005) in an experiment the participants must choose between 3 faces who was reliable and more attractive in a casual relationship: the faces most similar to the participant were considered reliable and the other attractants.
L ' reciprocal altruism and cooperation to carry out altruistic behavior predict that individuals are not related. In co-operation is a temporary behavior of altruism to get more benefits, mutual nell'altruismo expects the altruistic behavior is reciprocated at a later time.
reciprocal altruism is a risk for because DETECTION can not be returned.
Trivers (1971) points out the rules for success in this case reciprocal altruism:
1) the benefit to the recipient must be greater than those who do
2) the assistants should be social, live long and permanent residence , and then have the opportunity to meet again several times
3) must be able to recognize, therefore, have evolved a cognitive system
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