Questions involving the study of sex and reproduction, mating systems, sexuality, sex determination, gender, the evolution of sex, and other topics in the context of sex.

learn more… | top users | synonyms

17
votes
2answers
2k views

What's the difference between male and female?

As long as we only look at humans the differences are clear: males have chromosomes XY, produce sperm and don't get pregnant. Females have chromosomes XX, produce egg cells and bear babies. But when ...
16
votes
1answer
691 views

How do porcupines keep from pricking each other while mating?

How do porcupines keep from pricking each other while mating? It seems like they would constantly be scratching each other.
14
votes
1answer
15k views

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

There was question about what causes "morning wood." It was answered that the erection in the morning is caused by decline of norepinephrine during REM sleep. Which in part allows to prevent ...
14
votes
2answers
2k views

Why does sex last so long?

I wonder why (especially human) sex lasts longer than just a few seconds? My thought is that the shorter it takes a man to ejaculate, the lesser is the risk that he gets interrupted by a rival or a ...
14
votes
1answer
412 views

How do members of cryptic species know who to mate with?

According to Wikipedia: In biology, a cryptic species complex is a group of species which satisfy the biological definition of species—that is, they are reproductively isolated from each other—...
11
votes
2answers
1k views

Do males of all sexual species have Y chromosomes?

I know for instance some cells are sexual, so, this got me wondering, do the males of all species that have distinct sexes have Y chromosomes?
9
votes
1answer
15k views

What is the standard deviation of adult human heights for males and females?

The wikipedia article on human height reports mean height for many different countries by sex but it does not report standard deviations. What is the standard deviation of adult human heights within ...
9
votes
0answers
620 views

Evolutionary reasons why you cannot tickle yourself but masturbate

There are obviously good reasons that explain why you cannot tickle yourself (see e.g. here). This got me thinking why it is possible to masturbate... Wouldn't it make more sense to not being able to ...
7
votes
1answer
220 views

What is most ancestral: isogamy or anisogamy?

Sexual reproduction can be feasible with anisogamy (gametes of different sizes i.e. genders) or isogamy (gametes of same size i.e. mating types) or with undifferentiated gametes (i.e. true random ...
6
votes
3answers
530 views

Is homosexuality an adaptation in humans?

Homo sapiens have menopause - as some other mammals (e.g. some Cetacea) - a phenomenon where older females live for decades after the end of their own reproduction. Perhaps homosexuality, that looks ...
6
votes
2answers
736 views

Why sperm count matter for pregnancy?

In order for a woman to become pregnant, sperm is needed. Why is sperm count so important for pregnancy? http://en.wikipedia.org/wiki/Sperm
6
votes
2answers
540 views

Skin porosity in glans penis when erect

(Apologies if this is a too weird/inappropriate question in this forum. I only thought that I ask it since it happens to be part of human life.) The skin on a human typically blocks many substances ...
6
votes
1answer
267 views

When did our ancestors switch to a menstrual cycle instead of the estrous cycle?

The Wikipedia page on the Estrous cycle says: Humans have menstrual cycles instead of estrous cycles. They shed their endometrium instead of reabsorbing it. Unlike animals with estrous cycles, ...
5
votes
2answers
161 views

Can you tell the sex of a white willow when it's not flowering?

Can you tell whether a salix alba tree will produce male flowers or female flowers by looking at it, touching it or generally using your unaided senses? If not, is there any way to do that without ...
5
votes
1answer
313 views

Why are there so many sex determining systems in animals

There are several sex determining systems in animals. In mammals XY = male(except in rare cases where SRY crosses with genes on the X so that it is the reverse) and XX = female. In some birds it is ...
5
votes
2answers
137 views

If the haploid prothallium of a fern fertilizes itself into a diploid sporophyte, does this make all ferns clones?

From what I understand in the alternation of generations in ferns, mature spores germinate into a haploid prothallium. But how does this gametophyte produce recombinant gametes if it itself develops ...
5
votes
1answer
618 views

In males, why it is difficult to control orgasm?

Why it is difficult to control orgasm in male humans? How are orgasms controlled and what is different between males and females? We can control urine for few minutes, but we can't control orgasm for ...
5
votes
2answers
307 views

How Sex Evolved ? and when?

As I know evolution comes bit by bit mutation by mutation How sex evolved which requires a major change in at least two individuals one to become male and one to become female ? When that happened ...
5
votes
1answer
666 views

Do hormones make men think of sex?

I remember hearing a saying that goes like "men think of sex every 7 minutes (or seconds?)". I take this saying to mean that men have sex related thoughts more often than women. I'm interested if ...
5
votes
0answers
383 views

Genetic expression in interspecific hybrids

Referring to interspecific hybrids, I have the following two questions:- Quoting from wikipedia:- The offspring of an interspecific cross are very often sterile; thus, hybrid sterility ...
4
votes
2answers
36k views

Teens concerned about impregnation through clothes

Dry Humping, is: dry humping is the process of two people repeatedly moving up and down and back and forth on top of each other fully clothed( or missing various pieces, but the penis must not ...
4
votes
3answers
2k views

Do women experience more bonding hormones than men after sex?

Does Oxytocin (or any other bonding hormone) increase more so for women than for men after sex? Someone told me that it increases 4-fold for men and 12-fold for women (unconfirmed). Is there any ...
4
votes
1answer
444 views

Sexual Differentiation in Monoecious plants with unisexual flowers

In monoecious plants having unisexual flowers (eg Zea Mays, Ricinus Communis etc), there must be some mechanism as to produce two sexually distinct flowers from the same genotype. Since both the type ...
4
votes
1answer
255 views

How does sex differentiation work in Paracerceis sculpta, the sexually tetramorphic isopod?

Paracerceis sculpta is a marine isopod species known for its unusual reproductive strategy: female: medium-sized; lives in harems run by an α male α male: large; keeps a harem of females β male: ...
4
votes
0answers
181 views

Are there animal species with sex of an offspring determined by sex of preceding offspring?

For instance, if an animal's first offspring is male, then all subsequent offsprings will be male too (the sex of first offspring could be determined randomly). Does it happen in any species?
3
votes
5answers
1k views

Does any animal species have two sexes and more genders?

Does it exist any animal species that have two sexes and a kind of different internal diversification in two genders or more? I mean no something like different-task-based diversity but something ...
3
votes
1answer
285 views

Why do humans masturbate? [closed]

Why does masturbating seem to be like an addiction? What controls or initiates the urge to masturbate? Is it good or bad or both and why is it so? I have heard guys who say that the do it ...
3
votes
3answers
76 views

sex limited genome transmission

In general, for dioecious species, a large portion of the genome passed from parents to offspring of both sexes - in mammals the X-chromosomes and autosomes are passed from a mother to both daughters ...
3
votes
1answer
300 views

Advantages of bisexual reproduction over asexual one toward species promotion? [duplicate]

Are there any advantages of bisexual reproduction over asexual one towards species conservation and promotion? Do animals that have two or more sexes have more chances to reproduce? Does anybody had a ...
3
votes
1answer
115 views

Evolution from Mating types to different sexes

Imagine a lineage of multicellular organisms that had mating types and evolved their mating types into sexes. What are the possible mechanisms that might have brought this lineage to evolve sexes from ...
3
votes
2answers
235 views

Are gametes determined by the sex of an organism?

In the Wikipedia article for biological sex, I read the following sentence. "The gametes produced by an organism are determined by its sex:..." However, is it not through the gametes produced by ...
3
votes
0answers
87 views

What form of reproduction did the first land animals use?

What form of reproduction did the first animals on land use*? Were they hermaphrodites, or did they have male and female sexes? [Is there a proper term for sexual separation in a species?] Were any ...
3
votes
0answers
175 views

Electrodes in the brain and 'repetitive orgasms' [closed]

The advent of chlorpromazine in 1955 put an end to one of the more bizarre chapters in American psychiatry.$^1$ Dr. Robert Heath implanted wires or delivered injections of acetylcholine (a ...
2
votes
2answers
417 views

How to know if a woman is fertile without actually making her pregnant?

How to know if a human female is fertile (can give birth to child in future) without making her pregnant? Any signs, tests?
2
votes
1answer
1k views

How can I determine the gender of a tree seedling?

I would like to plant some home grown female mulberry trees in a circle, with a male plant in the center for pollination. How do I determine the gender of a tree seedling? I know it's possible, ...
2
votes
1answer
544 views

What is the result of meiosis?

Is the result of meiosis ONLY the sex gametes (male and female) which later meet to form a somatic cell? Sometimes I feel as if my book is hinting towards meiosis is the process where sperm cells meet ...
2
votes
1answer
232 views

Two-fold cost of sex and r/K selection theory

This article cites a bunch of articles (I haven't been through them) that the effect of the two-fold cost of sex is "reduced" in stable environment or in K-selected environment. It says: [..] the ...
2
votes
1answer
194 views

Does recombination increase the additive genetic variance for fitness?

On this article, first column, eighth line of the introduction: By bringing together favourable alleles from different chromosomes, sex and recombination increase the additive genetic variance for ...
2
votes
1answer
416 views

How do fully dioecious plants determine sex?

I know that a minority of plants are fully dioecious, with adult plants producing either only male or only female flowers. When is this sexual differentiation determined? Is the seed of such a plant ...
2
votes
0answers
33 views

What is the advantage of being tired after having a sex? [duplicate]

When we have a sex with partner, we feel so tired that we don't have any power to do anything. Then it would be disadvantage to the animals, of course humans too, for they are exposed to danger. For ...
2
votes
0answers
39 views

Why can't there be fructification of mycelium in submerged culture?

I am very new at this. I am wondering why fed batch cultures produce a lot of mycelia but no fruit. I thought the more mycelia you had, the greater chance of it forming a fruit body. I am refering to ...
2
votes
0answers
113 views

Why is gynodioecy common and androdioecy rare?

Gynodioecy is when a population features individuals that produce both male and female gametes and individuals that produce just female gametes. Androdioecy is when a population features individuals ...
2
votes
0answers
81 views

Ancestral states of sex determination system

Most (maybe all?) species that reproduce sexually have either genders (anisogamy) or mating types (isogamy). There exist today many different type of sexual determination system. There is a whole ...
2
votes
0answers
170 views

Is there a difference between endorphins that are released while physical activity and sex/masturbation?

I observerd myself and I can identify two different types of "happines". First - called by me - After Pleasure : Occurs AFTER (and last long) long activity that require from me engagement focus and ...
2
votes
0answers
81 views

Why did animals evolve genders? [duplicate]

The majority of animals have two genders, and both are needed in reproduction. It seems like it would be more advantageous for creatures to be hermaphrodites, since they could mate with any member of ...
1
vote
2answers
1k views

Can animals, like monkeys, be homosexual?

I heard that some monkeys can be homosexual? a friend of mine was saying that he saw a male monkey having sex with another male monkey in the zoo, I honestly didn't believe him, I think he just got ...
1
vote
1answer
103 views

Pseudosexual reproduction

Research projects with artificial life generally use creatures that are haploid. The offspring randomly inherit some genes from one parent, and some genes from the other parent. Q1: Are there any ...
1
vote
1answer
281 views

are female bonobos “always” pregnant?

Given that bonobo chimps are more sexually active then humans, are the females almost always pregnant? if not how not? also are they so sexually active in the wild as well or is it just in captivity?
1
vote
1answer
69 views

What is the evolutionary advantage of having pubic hair?

Only humans have pubic hair. What is the evolutionary advantage in having it?
1
vote
1answer
105 views

What is the current theory of sexual orientations in Biology?

What is the current explanation of what causes the different sexual orientations in humans.