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10

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 ...


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

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

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

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 ability to make decisions. You'll note that the work cited is done on criminals, patients and rats. ...


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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