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116

Short answer Yes, men and women's brains are different before birth. Background First off, learning effects versus genetic differences is the familiar nature versus nurture issue. Several genes on the Y-chromosome, unique to males, are expressed in the pre-natal brain. In fact, about a third of the genes on the Y-chromosome are expressed in the male ...


39

Sexes (male and female) are generally defined in terms of Anisogamy, which means that there are size differences between the gametes (i.e. the reproductive cells that fuse at fertilization). The sex with smaller gametes is defined as male and the sex with larger gametes is defined as female, and individuals that can produce both types of gametes are called ...


29

Very short answer No, not all males of all sexual species have Y chromosomes. You might want to have a look to the Wikipedia page on sex-determination systems. Long answer Diversity among the species that reproduce sexually Not all species that have sexual reproduction have sexes. Yeasts, for example, have mating types but no sex. Diversity among the ...


23

Women have erections too! These erections are called clitoral erection. Clitoral erections are usually accompanied with vaginal lubrification. Just like men (see here), the absence of norepinephrine during the REM phase of the sleep causes erections. In women, this phenomenon is called Nocturnal clitoral tumescence while it is called Nocturnal penile ...


20

Well, the answer by @An J has already explained the prima facie of your question which is: sperms need lower temperature for development. But I will be explaining in my answer: Why do the sperms actually need a lower temperature for their development? This is a debatable subject, but there have been several models or hypothesis about this. I found this ...


19

Summary: The idea that primary sexual determination defaults to female was proposed several decades ago and is primarily based on the observation that, in the absence of Sry, ovarian development takes hold. However, more recent models suggest that both ovary and testis development require complex genetic regulation and neither can really be said to occur by ...


15

It's probably around 7 cm for men and 6 cm for women. The Evolution of Adult Height in Europe, which is a source for some of the statistics reported on that Wikipedia page, gives averages, standard deviations, and sample sizes for both sexes across 10 european countries (and across a number of different age cohorts). Taking their numbers for men and women ...


14

The female stood with the tail held sharply to one side, and the quills on the back lying very flat. The male stood on his hind legs, while the front legs grasped the sides of the female. There was no repetition of the act. The male's urethra is 115-120 mm long, and his penis is 75 mm, so the he doesn't need to be as close to the female as one might ...


13

If there has been an ejaculation by the male, and semen is present, there is a chance of getting pregnant. Period. Teens really need to know that. I think you may have your terms confused - semen is the overall fluid released during an ejaculation, sperm are the cells with tails that are produced in the testes and fertilize the egg. At any rate, according ...


13

No. There are many sex-determination systems. Mammals and fruitflies use the XX/XY sex-determination system — except for the platypus, which has 10 sex chromosomes. ZW sex-determination system is used by birds and some reptiles. It's similar but with the male having two of the same chromosome (ZZ) and the female being the heterogametic sex (ZW). There's ...


12

There are plenty of animals with brief procreative periods, as you suggest. In chimps, sex takes 10 to 15 seconds - much less time than humans. So the question is really why have humans evolved to be different? I don't think any of the answers based on fitness are particularly compelling. It's not like sex feels like running a marathon or less physically ...


11

As both @Rory M and @Alexander Galkin suggest, there are various non-visual mating behaviors to allow these species to select mates and also allow taxonomists and researchers to identify these species. And they hit on the two major ones, courtship rituals (mating calls, throat bulging, dancing) and pheromones. Let's have a look at some two examples: The ...


10

It depends on just what you mean by "required", but insects such as bees and ants sort of meet the criteria. First, the double helix of DNA is inherently binary, so at the lowest level you need two and only two individuals for sexual reproduction. However, the actual process in the world may require more types. Take bees for instance. There are basically ...


10

There exists something like multiple sexes in fungi, but it's a bit complicated. First of all fungi don't actually have anything that represents the two classical animal sexes, phenotypically their reproductive cells are all equal (they have isogamic reproduction). However there can be certain alleles in some fungi species (sometimes multigenic, sometimes ...


9

Barnard's wonderful text "Animal Behavior: Mechanism, Development, Function and Evolution" offers some enlightening summary to the discussion of homosexuality in a biological context! Brief Summary to ch 12, page 606: What we know so far: homosexual behavior is recorded all throughout animal kingdom there are evidence for genetic basis to ...


9

According to textbook of forensic medicine and toxicology by Ks Narayan reddy: Qualitative differences are: Male mandible has everted ramus, but female have inverted ramus. Males have chin U shaped, but it's rounded in females Quantitative differences: Suparaorbital ridges are prominent in males but often absent in females. Mastoid process is wider, ...


8

I'm going to give a tentative answer full of speculation and guesswork, but it's too long to fit in a comment so here goes. Sex duration is possibly a sort of human reproductive handicap. Sexual arousal can soften the cervix, increasing fertility during lengthy sex sessions. Lengthy sex exposes them couple to predators and takes time and energy, so if you ...


8

Males and females mosquitoes are morphologically quite different. The majority of individuals you see are females. The males are not attracted to humans and so we see them less often. The main obvious difference is the size of the antenna. When you see the large feather-like antennas of a male, you'll have no doubt; it is a male. The male also tend to be ...


7

Many organisms have multiple sexes. For instance, here is one which apparently has 7 (and each sex, or "mating type" can only mate with the others). The "gotcha" is that, mostly, they're unicellular organisms where mating in itself is weird to begin with. I haven't ever heard of a metazoan which truly has more than one sex (there may be variation within the ...


7

Naked mole rat colonies contain individuals of both sexes, with one breeding female and one to three breeding males, and the rest non-breeding individuals of both sexes. The other individuals in the colony have an additional caste system that seems to depend on size but not sex (i.e., there does not seem to be a hierarchical relationship between non-...


7

One point of view you rarely see is the perspective of sex differences from an evolutionary standpoint. Never mind that this is the reason why the differences exist in the first place if they do at all. But the short answer is that Human Male and Female brains are unquestionably selected to be different (whether this means they are actually different ...


7

Sex vs Gender Sex is defined by the anatomy of an individual. The majority of people can safely be categorized as either male or female. There are exceptions and limit-cases of course such as intersex people for example. Gender is a social construct. It is therefore not the role of a biologist but the role of a sociologist to address the details of the ...


7

A mature human sperm has some mitochondria, a nucleus, an acrosome, and a flagellar apparatus. That's it. Because of the lack of other organelles in the sperm, they have to be kept in a kind of 'cold storage' so that they are viable for at least some time (usually a couple of days). The ideal temperature would be 1.8 °C to 2.5 °C below normal body ...


6

Of course. There's several fertility tests available to determine the quality and quantity of egg reserve, and whether or not the there are abnormalities in the uterus. However, some of them are invasive procedures, and all of them should be performed by a professional. I doubt the layperson would know what they're looking at on an Ovarian Ultrasound. If ...


6

There is absolutely no way to tell to be honest because mulberry trees have the capability of changing sex (reference). From a paper titled "Diversification of mulberry (Morus indica var. S36), a vegetatively propagated tree species", I quote The sex expression of plants appears to be a function of hormonal control; there seems to be evidence that ...


6

Could not fit in a comment… I don't quite know how to answer. I think that the only answer one could give is why not?. Various mechanisms may evolve under different life-history, different environment, different ecological strategy, different mutations occuring,.. In some species (including some amphibians) the evolution of sex determination system is ...


6

One word. DOPAMINE See this article on Reward System and this one on Dopamine Those basically answer your question as to addiction, urge, and feelings of relaxation. There is absolutely nothing wrong with masturbation, so long as you realize that it is a healthy expression of one's sexuality, that is observed, quite frequently, in our nearest relative, ...


6

So I've dug a bit into how a 'normal morphological' form is defined and characterised, since assessing morphology into 'normal' and 'not normal' is always a very tricky thing. Looking into the method section of the source you cited, we get: All laboratories generating the data analysed here used standardized methods for semen analysis [...] The ...


5

Does Oxytocin increase more so for women than for men after sex? Answer: Yes, Oxytocin level shoot up for female after sexual. It is highest at orgasm, which is the main cause women could have multiple orgasm. Someone told me that it increases 4-fold for men and 12-fold for women (unconfirmed). Answer: The level of oxytocin actually increase 5 times ...


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