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What is baffling,
Organisms need to replicate their genetic material in an efficient and reliable manner.
which is exactly contrary to the random, inefficient and unreliable business of sexual reproduction!
The fascination of that article is in that it begins by stating that nobody knows the answer. Worse, one of the hypotheses it offers starts with
Since hypotheses for the origin of sex are difficult to verify experimentally (outside of evolutionary computation), most current work has focused on the persistence of sexual reproduction over evolutionary time. The maintenance of sexual reproduction (specifically, of its dioecious form) by natural selection in a highly competitive world has long been one of the major mysteries of biology,
Scientists in France believe an intelligent blob expresses some 720 different sexes. The Paris Zoological Park is showcasing the ultimate gender fluid.
In this article per example we dont really talk about "sexuality" and like very often when we talk about genetic we forget to talk about the "plants" .And other lifeforms have many other sexual gender, not only two like the "blob"
Sex is what is determined by genes. Sexuality is identified by behavior. Gender is whatever an individual wishes it to be.
Some shark species are capable of asexual reproduction.To procreate, most species (sharks included) require the fertilisation of an egg by a sperm. But for some, it does not take two to tango. Through a natural form of asexual reproduction called parthenogenesis, some animals can produce offspring all by themselves.The term is a portmanteau of the Greek words parthénos, meaning ‘virgin’, and génesis, meaning ‘creation’.This form of asexual reproduction has also been recorded in other shark species such as whitespotted bamboo sharks, blacktip sharks and bonnethead sharks. According to a study published by Australian biologists, zebra sharks are also capable of making the switch from sexual to parthenogenetic reproduction after being separated from their male mates.Scientists believe this phenomenon occurs as a last resort for females that have an extremely hard time finding a mate. It typically happens to animals living in captivity, such as aquariums, where there are no other options available. In nature, parthenogenesis may happen as a result of human activity such as overfishing or anthropogenic climate change, where a large number of males have been wiped out.
Hermaphrodism is determined by genes (like every trait you would say), but then, hermaphrodites do not belong to a sex category ?
Also, we have some male and female sex differenciated species that can sometime also do parthenogensis, like the sharks.
But just to add to the confusion, don't forget eels and barramundi (and others I haven't caught) that change sex with age.
In butterflies, sex is determined by chromosome differences. But unlike in humans with the familiar X and Y, in butterflies, it is the females that determine the sex of offspring. Males are ZZ, while females are ZW. How do females compensate for the loss of genetic information? New research shows that, contrary to previously inconsistent findings, in all species studied, that the expression of Z-linked genes is consistently equalized between the sexes. They do so by either passing along either their Z (male) or W (female) chromosomes. Males are ZZ, while females are ZW. This ZW pattern is also prevalent in birds, some fish, and insects like butterflies. Similar to XY pairs, ZW pairs are different from each other in their shape and gene content: The Z chromosome is larger and has many genes, while the W consists mainly of repetitive DNA.
Wait, what?The Process of Sequential HermaphroditismTo understand what Finding Nemo got wrong, you have to understand sequential hermaphroditism. Hundreds of species of fish undergo this biological process, which is a kind of sexual transition. For scuba divers, perhaps the most identifiable (and beloved) undersea hermaphrodite is the clownfish, which is born exclusively male. Not all marine sequential hermaphrodites begin life as males; moon wrasses in the Indian Ocean and western Pacific, for example, all start off as females and become males, and some fish, such as Asian sheepshead wrasse, spend a number of years as one sex (Asian sheepshead wrasses are born female) and then switch gender. The mangrove killifish is both male and female; it self-fertilizes for its entire reproductive life. In fact, about 2 percent of fish species display some kind of hermaphroditism, or roughly 500 different species worldwide.Clownfish carry both female and male reproductive organs. In the female-dominated clownfish community, the female is the largest fish. She mates only with the breeding male, usually the second-largest and most aggressive male in the community. The rest of the community are made up of sexually immature males. When the female dies, the breeding male will get first choice of food and begin to gain weight, eventually becoming female.The biological change inside the fish is governed by hormonal changes—chemical shifts that trigger a complex and cascading effect,” says Marah J. Hardt, Ph.D., founder and CEO of OceanInk, and author of Sex in the Sea. For the transitioning male, the testes dissolve and ovaries form.
When they’ve decided they like each other, the seahorse females swim towards the surface of the water, and the males follow. The females then put their bright orange eggs into the pouch of the males through the hole at the top of the pouch. Once the eggs are safely inside, the males will add their sperm and shut the opening. The eggs are fertilised by the sperm, and then start developing into baby seahorses.With that, the job of the seahorse mum is done! She swims off, and leaves the father to take care of the growing babies. Inside the pouch, the babies grow eyes, tiny snouts, and little tails. It takes about 20 days for the babies to develop, safely tucked away from other animals that might want to eat them.
Environmental Sex DeterminationTemperature-dependent sex determination in reptilesWhile the sex of most snakes and most lizards is determined by sex chromosomes at the time of fertilization, the sex of most turtles and all species of crocodilians is determined by the environment after fertilization. In these reptiles, the temperature of the eggs during a certain period of development is the deciding factor in determining sex, and small changes in temperature can cause dramatic changes in the sex ratio (Bull 1980). Often, eggs incubated at low temperatures (22–27°C) produce one sex, whereas eggs incubated at higher temperatures (30°C and above) produce the other. There is only a small range of temperatures that permits both males and females to hatch from the same brood of eggs. Figure 17.20 shows the abrupt temperature-induced change in sex ratios for the red-eared slider turtle. If eggs are incubated below 28°C, all the turtles hatching from them will be male. Above 31°C, every egg gives rise to a female. At temperatures in between, the broods will give rise to individuals of both sexes. Variations on this theme also exist. The eggs of the snapping turtle Macroclemys, for instance, become female at either cool (22°C or lower) or hot (28°C or above) temperatures. Between these extremes, males predominate.
Early birds like Archaeopteryx were far too heavy to sit on their eggs without cracking them. The conclusion holds true for non-bird dinosaurs too, leading to fresh doubts about how to interpret spectacular fossils that appear to show dinosaurs brooding their eggs.Most birds today lay eggs with strong, hard shells. This strength is necessary because many birds practice contact incubation – meaning the adult rests its body weight directly on the eggs. But just because modern bird eggs can support the weight of a brooding adult it doesn’t necessarily follow that ancient bird eggs could, says Charles Deeming …
Many dinosaurs were likely warm-blooded with high metabolic rates that resembled those of modern birds, according to a study published yesterday (May 25) in Nature. Comparing samples from more than 50 vertebrate species, some modern and some extinct, researchers found evidence that endothermy, or warm-bloodedness, was already widespread before the mass extinction event at the end of the Cretaceous period, challenging the widely held idea that differences in metabolism explain why birds fared so much better than non-avian dinosaurs.
But the mechanical parameters of interest are the maternal pressure (weight per unit area) and the contact area of the eggs. A big fat momma might weigh several tons but spread the load over several square meters, and the crushing failure force on a small egg with a thick shell can be very large - particularly if applied at the pointy end.
There's little point in a coldblooded creature sitting on eggs other than to protect them from predators,