Spring, if you walk in the Chinese diving shallow area of the East China Sea or the South China Sea, Shanghai might happen to catch the rabbit "collective wedding." Several dozen Aplysia or lined up in clusters during the marriage, as if linked to a small mountain, like a chain. Do not make a fuss Aplysia bizarre behavior, but Aplysia hermaphroditic animals yo!
A Aplysia's body has both male and female reproductive organs. In marriage, when they both when the "husband", and when the "wife." In order to improve the efficiency of procreation, strung is the best choice.
Cixiongmobian animals
Linear nature of animals is one of the largest number of animal phyla. In the soil, oceans, fresh water, and plants and animals can be found in them. Nematode large family, there are many human and animal parasites, roundworms that we are most familiar kind of nematode. But there is a beautiful name Caenorhabditis elegans, tall very small, only 1.5 mm long. They are free, harmless to humans and animals live in the soil. From 1965 onwards, Caenorhabditis elegans to honor to become "the most learned," the nematodes in the field of molecular biology and developmental biology as a model organism to show their talents.
However, Caenorhabditis elegans sex is very strange that only two male and hermaphrodite sex. Hermaphrodite C. elegans sex chromosome is a XX male sex chromosome is XO type. XO in the "O" What does it mean? "O" is zero, there is no meaning. In meiosis, males of the two X chromosomes together, "deny" apart. Thus, these males nuclei under the microscope looks less of a chromosome, and more than a thick X chromosome. Although Caenorhabditis elegans chromosomes are the same, the above gene is the same, however, after a series of changes in the chromosome to form individual phenotype, namely reproductive system has produced a great change, grow a single leaf gonad, vas deferens, and a tail specialized for mating with. The normal separation of chromosomes androgynous there are two ovaries, fallopian tubes, uterus Tibetan Seiki and single. This is not a strange thing? Currently, scientists at the genetic level has not yet given a perfect explanation.
Caenorhabditis elegans male small number of individuals, only about 0.05%, and humans and other higher animals, 1: 1 sex ratio is very different. Such a low proportion, obviously vulnerable Well, is not it a bit difficult to find the object? In Caenorhabditis elegans groups, males just difficult to become men left, but rare, has become a well-deserved "men of God", androgynous individuals, and males will first rushing "marriage."
We eat scallops, actually hermaphrodite animals. After opening the shells, white cylinder is muscle tissue called the adductor muscle. It is outside the ovary orange, white and that there is a wrinkled testis. They want to "students" small scallops, eggs and sperm directly discharged in the sea, and let them free combination, not to engage in "close contact" between individuals.
Now, we know that sex is not only two, there are female, male and hermaphrodite, there is no more sex type it?
Gender inequality in the sky
What gender? Or Why have sex? Caenorhabditis elegans "rogue" It's the people around confused. Gender is an attribute of reproductive species. Different sex represents individuals in the reproductive process undertaken different missions. Humans and other mammals and birds rely on the type of sex chromosomes determine gender. Gender differences, the first is the difference between the various organs of the reproductive system, sometimes bring differences in body external features, like human secondary sexual characteristics, such as adult male Adam's apple, beard, adult women uplift breasts and so on.
The emergence of sex is the result of sexual reproduction, but sexual reproduction does not necessarily have sex. The first is sexual reproduction of microorganisms and protozoa and other lower organisms isogamy like mushrooms and other fungi is the case. These creatures appear in the genital While exchanges and recombinant gene, however, mating gametes provided by the parties on the shape, size and function is the same, can not make a distinction, and therefore there would be no sex. After that, the anisogamy. Gametes provided by the parties have differences in size, shape and structure. "Do not love the sport," "stay home", the other half still and wait the arrival of large gametes. Great gametes are generally from "female provided" in higher plants and animals called egg. Small gametes sports ability, to take the initiative to look for "life partner" rather male gametes called sperm in higher organisms. The size of the fusion of gametes to form a zygote, the fertilized egg is often called. Zygote grow into new individuals. In lower green algae, the algae truthfully ball, air ball algae and other organisms appeared anisogamy. Engaging reproductive paramecium and other protozoa, it can be seen as another type of anisogamy. Anisogamy emergence marked gender differentiation has begun to take shape up. The true sense of the emergence of gender, and age is generally considered more cells appeared similar, should be at least 600 million years ago.
The emergence of a gender division of reproductive and any division of full equality is impossible, within the same species, because inequality also appeared in the sky. Provided, only the male sperm genetic material, while the female egg but must be provided for the next generation of development of the necessary nutrients for the higher mammals and birds, the females sometimes have to nurture the next generation of sole task, but males often travel freely.
In the gender division of labor, some animals love extremes, the other gender oppression even to the extent of physical destruction. Love female tarantula grumpy, thuggish. If you come courting male tarantulas are not satisfied, simply eat it, also it is called: "In order to better nurture the next generation, to strengthen the point of nutrition." A type of male spider in South India Malabar coast learned to throw single-car, their mating process, will be tearing their genitals, do voluntary "eunuchs." Snapped genitals female spider will remain in the vagina, contraceptive suppository become, effectively prevent other male spiders sperm into the female body. Thereafter, these male spiders become brave and fierce, try to protect their spouses, not to meddle in other male spiders. After removal of the genitals and their weight loss of 4%, after removing some of the load of the male spider significantly enhanced endurance battle, often become the winner of the last laugh.
However, the animal kingdom also often sentimental, there are many "model Daddy." Long with a Malian hippocampus is a kind of fish, the hippocampus has a pouch on his father's stomach, where a small hippocampus day thrive under the careful care of my father's. Their mother did not like motherly love like, indifferent to their children. In the country, we often see a hen lying nest hatch. Antarctic emperor penguins care of the household, the man in the Lord, penguin dad all "super milk Dad," peace of mind at home and brood. They are facing the wind, standing about 60 days without food or drink until the baby hatch on the instep.
In human society, women were not so lucky, after the end of the first primitive matriarchal society, men are more due to the ability to obtain food, social status of men over women gradually prevail, women are reduced to a very long period of time secondary sexual position, not on an equal footing with men, in the 20th century the situation began to change. However, in certain countries and regions, and restraint in women is still a lot, if not enjoy equal right to education. This year, the Nobel Peace Prize 17-year-old Pakistani girl Malala Yousuf Karzai, from her childhood to risk their lives to fight for women's equal right to education, and religious forces to fight.
Carry out their duties, OK?
Reproductive division of labor leads to sex will bring gender inequality, discrimination and even sex. But why must the final organisms evolved sex, or that sex will bring about what kind of reproductive benefit from it?
In sexual reproduction, the biggest challenge is how to meet each other. Gender appears, life on Earth live in the ocean. Initially, these marine organisms produce gametes directly in the sea, improving the best way to meet a lot of probability that produce gametes so that "crowd", which greatly increases the chances to find the other half. However, not necessarily high-yielding. Biological parent's head, as "gamete" plant output is affected by the speed of biochemical reactions per unit time, and the raw materials available, that limit the amount of food. This kind of "Han troops more the better" strategy would lead to the number assigned to each of the nutrients can not be too much with the yard.
Met only one hand, those who grew up well is the final winner. To successfully grow, it is required to carry nutrients with house as much as possible. Anisogamy of male and female gametes functional division of labor just to solve this problem. Egg carry large amounts of nutrients, no quick action can be used as a target for a huge number of sperm to "Crash." This division of labor model is so successful that swept up to now, under the pressure of most species eventually natural selection, and embarked on a road of gametes carry out their duties, and this is the emergence of gender.
How to confirm their sex yet?
Person's sex from six different levels of judgment that sex genes, chromosomal sex, gonadal sex, genital sex, psychological sex and gender.
In mammals, if the sex chromosomes XX type was if the sex chromosomes XY type, compared with males. Instead of birds and mammals, the same chromosome is the male, called ZZ type, different chromosomes is female, called ZW type.
At the genetic level, has now been found more than 10 kinds of genes involved in sexual development, from different stages of fetal development were regulating sexuality, any one to go wrong, will go wrong sexual development. But generally the SRY gene as a sex determining gene, SRY gene that is having, then develop into a boy, does not have the SRY gene, then develop into a girl. However, Eastern Europe and Japan mole vole no SRY gene, it is defined as the production of a large female gametes (ie germ cells) of that party.
Gonadal sex constitute the main means of gonadal tissue. When the boy's gonads with testicular tissue, ovarian tissue girls gonad, gonads testicles, regardless of how the shape of the vulva are divided into boys and girls close if genital morphology is called male gonad to ovary, then divided into girls, if vulva like a boy, called female pseudohermaphroditism. Only gonads containing both ovarian and testicular tissue, it is called true hermaphroditism.
Human genitalia can be divided into inner and outer portions. Genitalia sex is the most familiar method of sex, which according to the shape of the external genitalia under direct vision to divide boys penis, scrotum and testicles, girls clitoris, labia and genital sex generally require professional inspection determined for boys spermatic cord, prostate and seminal vesicles, girls uterus, fallopian tubes and ovaries, etc.
Psychological Gender refers to an individual's own gender identity, this aspect influenced by genetic factors, on the other hand with education and family-related roles identified. Gender identity from 1 to 2 years of age began to form, 3 to 5 years of age is substantially complete.
Gender person is generally called gender. Mainly refers to the family, friends, people around, social institutions and legal agencies, such as a person's gender identity.
(Author: Xu Xiuhua)
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