Gender/Sex
Abstract:
99.99% of the population is biologically a male or a female.
If you are not a biological male or female you have a disorder of sex development which is a genetic disease or a developmental abnormality.
99.983% of the population identifies as a male or female.
If you do not identify as your sex you have a psychiatric condition called gender dysphoria.
No, there aren't 52 or however many genders. This is pseudo-scientific nonsense.
Comprehensive Analysis:
Current medical science states that there are 2 main genders/sexes in humans. There are of course people with underdeveloped gonads or missing gonads or an underdeveloped mix of both. They are grouped under the term Disorders of Sex Development (formerly called intersex) Even if we used the broadest definitions of gender dysphoria and disorders of sex development we would get that 99.983% percent of the population is and identifies as either male or female.
Gender dysphoria: 0.014% natal males + 0.003% of natal females = 0.017%, 100% - 0.017% = 99.983%
According to DSM-5 (the psychiatric diagnosis bible basically), the prevalence of gender dysphoria is 0.005-0.014% for adult natal males and 0.002-0.003% for adult natal females. [1] In Europe, 1 per 30,000 adult males and 1 per 100,000 adult females seek sexual reassignment surgery (SRS).
Gender dysphoria is where one person does not identify with the sexual organs they are born with but instead they want to be or think they are the opposite sex. Currently, gender dysphoria is a psychiatric diagnosis.
DSD: CAH (the most common DSD) = 1 case per 15,000 live births or 0.005% of the population. Adding in another 0.005% for other causes of DSD other than CAH leads to 0.01%. 100% - 0.01% = 99.99%
Analysis of worldwide infant screening of 6.5 million newborns found the incidence of CAH (congenital adrenal hyperplasia) to be 1 case per 15,000 live births. 0.005% of the population.
CAH is the most common Disorder of Sex Development.
Syndromes like Klinefelter Syndrome or 5-alpha-reductase-deficiency and others are genetic abnormalities that lead to gender/sex ambiguity. Some genetic diseases can make your cells have XXY chromosomes or XYY or others. They usually lead to sterility (an inability to reproduce) and such they remain in very small numbers since through evolution the normal arrangement of XX or XY chromosomes is the most advantageous for reproduction.
Hypospadia (underdeveloped penis) occurs at a rate of 1 case per 300 live male births. This does not lead to gender/sex ambiguity.
Testosterone and Estrogen both affect the developing brain and affect the person throughout their life. Females have low levels of testosterone just like males have low levels of estrogen. This of course varies from person to person.
No surgery or hormone therapy will ever change the XX or XY or other chromosomes in our cells. This is not affected by epigenetics (environmental effect on genes).
As per biology our goal in life is to reproduce. If we do anything to stray from this goal or are affected by an ailment that makes us stray from this goal we are less fit and will be more likely to be naturally selected out of the gene pool. This is why in the long term 2 main sexes/genders have persisted. Sexual reproduction is necessary also to maintain diversity in our genetics.
Sources:
Medscape.com
1) American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. 5th. Arlington, VA: American Psychiatric Association; 2013. 451-9.