I read here about human asexuality, and I cannot figure out if it's real or if people are just making stuff up. Have studies been done about this phenomenon and what explains it?
Yes, but until now only hypotheses on reasons for asexuality are available. Experiments on male gerbils show refused mating with female gerbils, indicating there are epigenetic, prenatal period factors causing diff. sexual orientation/behaviour:
A study on Mongolian gerbils showed that part of a population of male gerbil fetuses that developed between two female fetuses refused to mate, but instead spent almost 50% more time taking care of the young than male gerbils who as fetuses were positioned between two other males. They were also about 30% more likely to stay with a nest when the mother had left. This suggests that, although not perpetuating their own genes, they helped perpetuate their sisters' genes, which has evolution benefits for at least half that family's genes
For humans there has to be distinguished between an asexual lifestyle and sexual excitability/reduced libido, as some self-called asexuals are masturbating and obviously can feel orgasms, better called auto-sexual. Currently from a scientfic point of view there is no clear definition, but above mentioned properties would be obviously crucial. These articles sheds some light on classification of several defintions and genuine causes.
There have been very few studies about asexuality in humans, most of which were about the stereotype that disabled people are made asexual as a result of their condition. One of the only studies that looks at asexuality as a possible orientation was actually a reexamination by Anthony F. Bogaert of a survey of 18,000 British about general sexuality and STDs. 1.05% of the respondents to the survey reported "I have never felt sexually attracted to anyone at all," very close to the 1.11% who responded they were homosexual or bisexual, although more women tended to be the former than the later, and more men tended to be the later than the former. Bogaert noted this asexual group to have poorer health, shorter stature, less body weight, higher attendance at religious services, lower socio-economic status, and asexual women had a later onset of menarche, all when compared to sexual people. Although these are only correlations, they may help form later hypothesis about the cause of asexuality, and whether asexuality is a valid orientation at all. Bogaert suggests some of his own. Perhaps the factors affecting height growth and weight gain also affected a region of the brain vital to sexuality, or education or other resources dependent on socio-economic status are somehow vital in sexual development, or maybe asexuals had fewer "sexual conditioning" experiences growing up (i.e. masturbation) which might also explain the high proportion of women and religious (both groups are less likely to masturbate). Youth, however, was not correlated with asexuality, indicating these individuals were not merely "late bloomers;" asexuals actually tended to be older. Major limitations to the study, besides being merely correlative and not actually about asexuality, include its high non-response bias (30%) and its face-to-face style of interviewing (which may have pressured individuals to alter their answers). However, the study does contain enough correlative evidence to warrant future research in the area. (6)
So phenomenological asexuality seems more to be a female "property", making a epigenetic more plausible than pure genetic causing of asexuality, as one would expect equal distribution.
Differences in human brain structure indicate, that asexuality is also not caused by purely psychological/social development reasons
Since scientists have already noted that the brain of homosexual men is structurally different from that of heterosexual men (cell structure of gay mens' hypothalamus more closely resembles that of a heterosexual female's), that the asexual brain may too be structurally different should not be too easily dismissed. The existence of animal displays of asexuality run contradictory any suggestions that asexuality is a problem caused by psychological issues such as fear of commitment, or conscious/unconscious repression of sexuality, as animals are presumed to be incapable of both, although this rests upon the assumption that asexuality has the same cause in humans and animals
From an evolutionary point of view one has to ask how likely a pure genetic heredity of a general asexual property is, as humans mainly bear single not several babies and the development help similar to the mentioned gerbil case cannot play a role.
Asexuality as a mammal phenomenon exists, but currently its not clear how much genetic, epigenetic and post-birth development factors actually contribute to this phenomenon. But current knowledge emphasize factors influencing fundamental brain structure rather than psychologigal/social reasons.
Special cases like genetic caused Asperger, Autism reducing will of physical closeness to other humans show set of difficulties defining and reasoning asexuality on humans.
It is estimated that ~1% of population is asexual (at least in the UK).
Source: http://articles.cnn.com/2004-10-14/tech/asexual.study_1_sexuality-new-study-new-scientist?_s=PM:TECH (discussing a study by Anthony Bogaert, a psychologist and human sexuality expert at Brock University in St. Catherines, Ontario)
Bogaert's analysis looked at responses to another study in Britain, published in 1994. That study was based on interviews of 18,000 people about their sexual practices.
It offered respondent a list of options. One read: "I have never felt sexually attracted to anyone at all." One percent said they agreed with the statement.
However, it doesn't look like there are a lot - or any - studies on the topic which are more legit (e.g. not based on "have you had sex recently" surveys)
Recalling the teasing due to my 'eponymous' syndrome in 7th grade, there is such a thing as Turner Syndrome which leaves a person with a single X chromosome. Such a person would be asexual (although female), as the lack of the second X chromosome somehow inhibits development during puberty.