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121 votes
Accepted

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 ...
AliceD's user avatar
  • 52.5k
27 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 ...
Ben Bolker's user avatar
  • 5,364
24 votes
Accepted

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 ...
canadianer's user avatar
  • 17.8k
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 ...
user 33690's user avatar
  • 1,955
18 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 ...
John's user avatar
  • 14.7k
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 ...
Nicolai's user avatar
  • 4,391
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 ...
jamesqf's user avatar
  • 3,643
12 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, ...
mgkrebbs's user avatar
  • 9,054
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 ...
acvill's user avatar
  • 8,296
9 votes
Accepted

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, ...
JM97's user avatar
  • 4,826
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 ...
Tyler S. Loeper's user avatar
7 votes
Accepted

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 ...
Bryan Krause's user avatar
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7 votes
Accepted

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 ...
AP2261's user avatar
  • 392
6 votes
Accepted

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 ...
MattDMo's user avatar
  • 15.3k
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 ...
Remi.b's user avatar
  • 68.1k
6 votes
Accepted

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, ...
JayCkat's user avatar
  • 2,922
6 votes

In men, why do over 80% of sperm have abnormal form?

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 ...
Nicolai's user avatar
  • 4,391
5 votes

How is trangender female different from normal female biologically?

Let's first consider the difference between the concepts of sex and gender. The distinction between sex and gender differentiates sex (the anatomy of an individual's reproductive system, and ...
Remi.b's user avatar
  • 68.1k
5 votes
Accepted

What is inside the male’s body in the space where females have the ovaries and the uterus?

Wider hips in females is not contributed because of large volume of organs. Broadening of the hip bones happens as a feature of the female pubertal process, and estrogens (the overwhelming sex ...
Imtiaz Raqib's user avatar
  • 1,278
5 votes

Are there lifeforms that have more than 2 sexes?

Yes in many different way. No for a species in which all three are required at once. there are species that have more than one type of male or female, each with drastically different body plans, ...
John's user avatar
  • 14.7k
5 votes

Why is sex hurtful for some animals but pleasurable for others?

There are various selection pressures that may lead to sex being more or less harmful. I don't think there is an easy way to summarize these selection pressures other than just going through load of ...
Remi.b's user avatar
  • 68.1k
4 votes
Accepted

Is the term 'allele' specific to sexual populations?

No, it's fine to use for asexuals too. There's an ambiguity in the term "locus" for asexuals, but "allele" is fine, and "gene" is not much more ambiguous than it is for sexuals (which isn't saying ...
Daniel Weissman's user avatar
4 votes

Does any animal species have two sexes and more genders?

Yes, it is called Alternative Mating Strategies and is well known. As an example High-backed pygmy swordtail (a fish) are known for having two types of males, one that is large and aggressive and ...
John's user avatar
  • 14.7k
4 votes

Why are (some) male humans sexually attracted to the breasts of female humans?

Short answer, we don't know. There are several competing hypotheses but they are all nearly impossible to test. Behavior often suffers the same problem as testing, we can come up with a hypothetical ...
John's user avatar
  • 14.7k
4 votes
Accepted

Y chromosome changing sex ratios

This sort of thing absolutely happens; useful search terms are "sex ratio distortion", "segregation distortion" (i.e. modifying the ratios with which different chromosomes ...
Ben Bolker's user avatar
  • 5,364
4 votes

higher-order evolutionary adaptations

I think that you are talking about evolvability (as I see it). Sex is indeed a sort of a meta-adaptation, see e.g. The Evolution of Sex by John Maynard Smith. The math for this is rather well ...
Maximilian Press's user avatar
3 votes

Why are there so many sex determining systems in animals

Here's just the paper for you: Sex Determination: Why So Many Ways of Doing It? (Bachtrog et al, 2014.) (And, it's open access!) One important point is that although the initial "triggers" are ...
David Bahry's user avatar
3 votes

Which species has the highest proportion of homosexual individuals?

Homosexual behavior have been observed more than 1500 species (according to Museum of Natural History of the University of Oslo). A full comparison between all known species is far beyond the scope of ...
Remi.b's user avatar
  • 68.1k

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