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The Myth of Gender Dimorphism and Biological Sex

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Jonade Naeem

on 21 February 2014

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Transcript of The Myth of Gender Dimorphism and Biological Sex

Animal Rainbows
Sexual diversity exists everywhere in life. In many cases, sex roles are reversed, if not completely different than we understand of gender.
Biological Definition of Sex
Males produce small sex cells

Females produce large sex cells
Is gender dimorphic in nature?
Darwin's theory of natural selection was not only elegant, but dangerous.
Male= XY
Female= XX
Human Rainbows
The Myth of Gender Dimorphism and Biological Sex
Body Sizes Reversed
Anglerfish males are tiny and called "dwarf males". These fish are incapable of independent existence. They have large nostrils to hone in on females, pinchers to grasp onto females. Epidermal tissues fuse and their circulatory systems unite. The male becomes an organ of the female. Multiple males can attach forming a non-parasitic colony, where nutrients are shared.
Sex Roles Reversed
A female seahorse places eggs in a male's pouch. The eggs are fertilized there, forming embryos, and the male becomes "pregnant". The male provides oxygen, maintains the right salt balance, and nourishes and protects the embryos in his sac.
What sex are you?
There is difficulty in defining sexual differences. Which lens should we choose?
Yet, Darwin's theory of sexual selection remains unchanged.
Darwin proposed a universal idea for social life in animals, "It is certain that amongst almost all animals there is a struggle between males for the possession of the female...The strongest, and...best armed of the males...unit with the more vigorous and better nourished females...[and] surely rear a larger number of offspring than the retarded females, which would be compelled to unite with the conquered and less powerful males."

The Descent of Man, and Selection in Relation to Sex
Accepting natural selection meant accepting all people as belonging to one species.
Colonization was a central tool in justifying efforts to colonize, enslave, and even exterminate people. If it could be established that certain kinds of people were indeed less than, even less than human, then it was acceptable to treat them as such.
But, even Darwin saw exceptions.
"Taking as our guide the habits of most male birds... [females] endeavour to drive away females, in order to gain posession of the male...the males would probably be most charmed or excited by the females...sexual selection would then do its work, steadily adding to the attractions of the females; the males and the young being left not at all, or but little modified."
How does this open the possibility of seeing sexual identity with greater diversity?
M2F and F2M and MF crisscrossing is regularly found.
Transitioning common.
But, hermaphodites common.
plants, marine invertebrates and other evolutionarily "older" organims exhibit hermaphrodism.

If hermaphodism is the original "norm", how might this challenge our understanding of the concept of normal?
Female clown fish are larger than males. If she is removed , a remaining male turns into a female.
Intersex in Animals
gonads: place where eggs and sperm develop.

external plumbing: penis, clitoris, scrotum, labia;

internal plumbing: fallopian tubes, muellerian ducts.

intersex is a combination of any, or all of these components, whether they are functional (sex-cell producing) or not.

Intersexuality in Mammals
16% of kangaroo rats have both sperm-and egg-related plumbing, including a vagina, a penis, a uerus, and tested in the same individual.
10-20% of female bears in some populations have a birth canal that runs through the clitoris, rather than forming a separate vagina. An intersex female bear actually mates and gives birth through the tip of her penis.
Female spotted hyena mates and gives birth through her penile canal. Birth is usually very difficult. Female spotted hyenas have a dominance hierarchy, and the erect penis is a signal of submission. It also a form of greeting between females.
ZW sex-determining system
determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), and some reptiles, including komodo dragons. In the ZW system, the ovum determines the sex of the offspring
Male determines sex.
Humans, most mammals, and some plants.
Sex is complicated.
everyone has the genes to make both ovaries and testes, but which we make depends on a network of codependent genes.
Story of Y
believed to have evolved as a mutation of a chromosome when monotrenes (egg-laying mammals with ZZ/ZW system) split from therians (non-egg-laying XX/XY).
SRY is a gene found on the Y-chromosome, and with the help of other genes(found on non-sex chromosomes), controls the development of some male characteristics. Changes to these genes can affect sex presentation.
Many of the genes that control sexual development are found on the autosomes
very few genes are found on Y-chromosome when compared to X
highly mutable and varied between mammals in terms of expression and regulation (can be expressed sometimes only once, at particular times, or not at all!).
Crossing over can result in a Y chromosome missing an SRY gene.

What would this mean?
The story of X
only one X chromosome is activated in females. Which X chromosome is activated can differ from tissue-to-tissue.
differences between the genes expressed between two females can be greater than that between two males (although it may not physically appear this way)
males also express the X chromosome, and in some cases, louder than the Y, giving them "female" characteristics.
Congenital adrenal hyperplasia (XX)
The most common cause of sexual ambiguity is congenital adrenal hyperplasia (CAH), an endocrine disorder in which the adrenal glands produce abnormally high levels of virilizing hormones in utero.
Androgen insensitivity syndrome (XY)
People with AIS have a Y chromosome, (typically XY), but are unable to metabolize androgens in varying degrees.
Cases with typically female appearance and genitalia are said to have complete androgen insensitivity syndrome (CAIS). People with CAIS have a vagina and no uterus, cervix, or ovaries, and are infertile.
5-alpha-reductase deficiency (5-ARD) [XY]
The condition affects individuals with a Y chromosome, making their bodies unable to convert testosterone to dihydrotestosterone (DHT). DHT is necessary for the development of male genitalia in utero, and plays no role in female development, so its absence tends to result in ambiguous genitalia at birth; the effects can range from infertility with male genitalia to male underdevelopment
Turner syndrome
It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent or has other abnormalities
Triple X syndrome
It is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. There is usually no distinguishable difference to the naked eye between women with triple X and the rest of the female population.
Klinefelter syndrome
Klinefelter syndrome is a genetic disorder in which there is at least one extra X chromosome to a standard human male karyotype. Principal effects include hypogonadism and sterility. A variety of other physical and behavioural differences and problems are common.
XYY syndrome
Boys with the 47,XYY karyotype have an increased growth velocity from early childhood, with an average final height approximately 7 cm (3") above expected final height
XX male syndrome
There is a rare sex chromosomal disorder. Usually it is caused by unequal crossing over between X and Y chromosomes during meiosis in the father, which results in the X chromosome containing the normally-male SRY gene. When this X combines with a normal X from the mother during fertilization, the result is an XX male.
Swyer syndrome
A type of hypogonadism in a person whose karyotype is 46,XY. The person is externally female with streak gonads, and left untreated, will not experience puberty.
Even more!
Other chromosomal variants include XXYY, XXXY, XXXXY
This is just chromosomal differences. Sex binaries are disrupted by hormonal influences, embryological development, and post-zygotic (after-birth) changes.
What do you think?
Do you think Darwin's idea of sexual selection need updating in light of new information? What benefits and risks would this pose to society?
How should intersex individuals contend with their sexual and gender identity?
In light of this new information, do you think sex is a social construction?
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