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120 votes
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Are male and female brains physically different from birth?

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 ...
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42 votes
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What's the difference between male and female?

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 ...
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29 votes
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Do males of all sexual species have Y chromosomes?

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 ...
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24 votes
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What is the female equivalent of the morning erection that some men experience?

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 ...
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24 votes
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Is female the default sex in humans?

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 ...
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21 votes

Is sex a spectrum?

Short answer: it's messy, and probably no answer will satisfy everyone. I'm only going to consider sex (I'm not going to mess with "gender") in humans. It's reasonable to consider sex as ...
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20 votes

Why do hot water baths affect only males' fertility? Why not females'?

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 ...
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  • 1,955
15 votes

Are there lifeforms that have more than 2 sexes?

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 ...
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  • 4,296
15 votes

Is sex a spectrum?

First gender and sex are not the same thing; as an old teacher of mine glibly put it, "sex is plumbing, gender is clothing," and even that is a gross generalization. The problem you are running into ...
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14 votes
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Teens concerned about impregnation through clothes

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 ...
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13 votes

Do males of all sexual species have Y chromosomes?

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 ...
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13 votes

Are there lifeforms that have more than 2 sexes?

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 ...
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12 votes
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Why does sex last so long?

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 ...
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  • 6,771
11 votes

Why are men more susceptible to severe COVID-19?

Update -- In the time since this question was asked, two relevant articles have been published, one in Nature Reviews Immunology and one in medRxiv (note: medRxiv is a preprint server and is therefore ...
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9 votes
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Can you tell if a corpse was male or female by only examining its skull?

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, ...
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  • 4,716
8 votes

Why does sex last so long?

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 ...
8 votes

Is homosexuality an adaptation in humans?

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 ...
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  • 1,871
8 votes

How do you identify a mosquito's sex without letting it bite you?

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 ...
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  • 67.5k
8 votes

Are male and female brains physically different from birth?

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 ...
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8 votes

Is there any evolutionary reason why male traits appear in the heterogametic sex and female traits in the homogametic sex?

The title question, Is there any evolutionary reason why male traits appear in the heterogametic sex and female traits in the homogametic sex?, suggests that male always is the heterogametic sex, ...
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  • 8,718
7 votes

Why are there so many sex determining systems in animals

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 ...
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  • 67.5k
7 votes

Does any animal species have two sexes and more genders?

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 ...
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  • 4,470
7 votes
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Why do humans masturbate?

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 ...
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  • 4,970
7 votes
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Are all non-breeding naked mole rats the same sex?

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 ...
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7 votes
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Why do hot water baths affect only males' fertility? Why not females'?

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 ...
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  • 392
6 votes
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How can I determine the sex of a tree seedling?

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 ...
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6 votes
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How is trangender female different from normal female biologically?

Remi gives a good introduction to the various terms and definitions you should know when learning about gender identity. However, he didn't really address your basic question: What is biological ...
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6 votes

How many genders are there?

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 ...
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  • 67.5k
6 votes
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Is it Theoretically Possible to Create a Male clone from the donor Cell of a Female?

So, i want to know if the sex of the resulting clone is determined by the sex of the donor animal. Generally yes for mammals and birds. In animals where the sex is determined by sex chromosomes, ...
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