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12

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 ...


9

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 ...


5

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 ...


5

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 ...


5

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 ...


4

I remember overhearing a botanist some 10 years ago, that he cannot tell male poplar from female when they are not flowering or producing seeds. Poplars and willows are related, so it is a weak indication for you, you will likely not find any visible features in willow neither. But it is an old information, too. (Are you interested in DNA sequencing ...


3

Interestingly it does seem as if this is at least in part the case. Testosterone levels are tied to sexual impulses, but also risky behavior and aggression. Its responsible for sexual drive in women as well. Low testosterone can cause depression and loss of the ability to make decisions. You'll note that the work cited is done on criminals, patients ...


3

Sex (depending on how you define it), evolved very early (more than a billion years ago). Even species like yeast have a type of "sex" (see below). Also, this doesn't mean there is necessarily a big difference between the two sexes. The yeast Saccharomyces cerevisiae, for example, also has two "sexes", called mating types. One is called alpha and the other ...


3

I will be able to answer only a part of the question. Sex determination in Zea Mays Initially, all the flowers in the plant are perfect, ie they have both the male and the female flowers. This is followed by abortion of stamen or pistil resulting in unisexual flowers. Which part of the flower undergoes abortion is determined according to the location of ...


3

Cases of homosexuality have been described in numerous species, including primates, and the wikipedia link posted by @shigeta lists and describes some of them. It could be difficult to untangle the difference between an animal not being able to identify sexes very well, or, deliberately mating to anyone and those actively making a choice to engage in ...


3

If you are talking potential for fertility. There are a few... Having regular periods Healthy weight. Extremely thin women tend to stop ovulating. Obesity also impairs fertility by altering hormone levels. Whether she has been using birth control (i.e., "the pill") in the recent past. It takes a while for the body to get back to normal. Smoking impairs ...


2

In most species, females are pregnant as often as they can be. Since the availability of sex is rarely a limiting factor, it seems likely that female bonobos are as "always" pregnant as other chimps and socially living primates. The actual rate of pregnancy will be hormonally limited by things such as reduced fertility during lactation and so on.


2

Shuster, SM & C Sassaman (1997) Genetic interaction between male mating strategy and sex ratio in a marine isopod. Nature 388: 373-377 As described in this paper, the chromosomal system of sex determination in Paracerceis sculpta is ZW=females, ZZ=males. Genetic evidence indicates that the morph of a ZZ male is determined by a second locus, Ams ...


2

The short answer is that in dioecious plants the sex of an individual plant is determined by its chromosomes. Several familiar crop plants are dioecious: asparagus, kiwi, hop, papaya, spinach and yam. The evidence indicates that dioecy has evolved independently in different plant families. I refer you to Matsunuga & Kawano (2001) Sex determination ...


2

Generally, all diploid species pass through a haploid phase in their life. This is called the alternation of generations and the cycle may be presented like this: Commonly we see organisms that spend most of their life in the diploid phase, with greatly reduced haploid phase (e.g. humans "live" in haploid state only as gametes). However, this is not the ...


2

This is not on theoretical grounds, but here is an existence proof: a number of bacteria, which reproduce asexually, are polyploid. Here is a blog I really like informally discussing the concept of ploidy in bacteria. The example I am familiar with is cyanobacteria, which can have 3-4 all the way up to 142 copies of its genome, according to this paper (1). ...


2

I can only offer a partial answer on the theoretical aspects. I don't know if you are familiar with the mid-90s papers by Otto et al. (Otto & Goldstein,1992, Otto & Marks, 1996), but these are definately relevant to your question. They deal with the "masking hypothesis" of diploidy, i.e. that deleterious mutations can be masked by "healthy" alleles, ...


2

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 ...


2

Hermaphrodites and gender changing (M->F F->M) fish I have heard of. There are also occasionally individuals who are neither male or female, which may or may not count here. But 3+ separate genders I haven't seen except for fungi, which might occasionally be multicellular, but probably not what you are thinking of. Fungal genders are so many because they ...


1

r/K selection has become less of an important heuristic for characterizing a given species' strategy of reproduction and less a matter of predicting what sort of species will emerge from a given environment as it had originally been proposed by MacArthur and Wilson in 1967. The paper you cite tries to determine whether rotifers become more r or more K ...


1

It could definitely not fit in a comment… Those are very good questions. Unfortunately answers are not easy and ask for writing a lot! But maybe someone will give it a try. Note that the evolution of recombination and of sexual reproduction are not quite the same. Also, evolution of sexual reproduction is not the same than evolution from various ...


1

The oldest evidence we have of sex comes from the fossil record which shows it was present more than one billion years ago - it could be even longer (it would be naive to think we have found all fossils or that all organisms that ever existed became fossilized). Sexual reproduction introduces potential benefits because it allows recombination meaning useful ...


1

It seems we have more hypothesis than theories. There is a book called "The Moral Animal", by Robert Wright, where he cites some researches relating order of birth with sexual orientation (of course, not a 100% direct relationship). That's for the proximal cause. For the distal cause (evolutive) it makes sense to me that we are a sort of "eusocial" species, ...


1

Could the unison of such divergent sets of alleles theoretically lead to unique phenotype and features that bear little resemblance to any features belonging to the parents? Though it is possible that some unique characteristics may emerge but it is very less likely that the offspring will bear no resemblance to the parents. You start with an ...


1

My hypothesis is "Yes", that is "Early human beings are far more promiscuous than we are now". So how i came up this? Cos Human came from Chimpanzee right? No. Also, when human evolved, they started to realized that promiscuousness wss not healthy & not good for society I'm sorry, what ancient society are you claiming cracked down on ...


1

Another important reason to have mating types is to prevent self-fertilization or self-polination that produces less capable offspring. Because of this requirement, mating types may evolve also for species that produce both types of gametes, or does not differentiate them into male and female gametes. Fertilization is only possible if gametes have different ...


1

Hopefully this syllogism will answer your question. Given the following premises: In the absence of selection, fitness of individuals are at a theoretical maximum. If a theoretical maximum fitness is achieved then effective population size is maximum. If there is an allele that confers both increased and decreased fitness you have a genetic conflict (e.g. ...


1

This is a little tricky. First of all lets be clear about 'bringing together favorable alleles' (or any alleles) represented by site mutations on 2 chromosomes: --------A------------------ X ------------------B-------- If the two dashed lines are two copies of the same chromosome, then a recombination event at X may produce: ...


1

Now, I know my obsession with this question is crazy :-D. I took the suggestion of Oreotrephes. This is what to look for under the tree - friut and seeds: . Source.


1

Here's a Ted talk about a case of homosexual necrophilia in mallard duck. The speaker lists a few other examples of weird animal mating (frog with a fish). Apparently animals may have non-traditional preferences as well as humans. The talk does not deal with whether this is a pathology or not, just lists a few weird examples. Additionally, there's this ...



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