The difference between men and women

I had the pleasure this evening of introducing Prof Root Gorelick to give a lecture to the local Centre for Inquiry group here in Ottawa.  I have seen him give a number of relatively provocative talks at conferences and I knew his engaging style and fascinating subject matter would make for an interesting evening.  Some people have asked me to summarise the talk as they couldn’t make it, so here is my best attempt while it is still fresh in my mind…

Dinosaurs likely lacked external genitalia

Root’s research focuses on the evolutionary origins of sex and the sexes.  However, he started with a very anthropocentric view of sex and gender, looking at the differences between men and women.  He pointed out the notion of “phallometrics”, where a newborn child’s phallus was considered “clitoris” if it was below 0.8cm and “penis” if above some other arbitrary length.  Those people who fall in between the two categories (and that is not a trivial proportion of newborns) are faced with a choice: do you leave it as ambiguous or do you “normalise” the child (*snip*).  It turns out that the length of the phallus is no more an indicator of gender than height.  This is further complicated by conditions such as congential adrenal hyperplasia (CAH) which cause masculinisation of females due to the release of androgens from the adrenal glands.  Many people consider the XY-XX dichotomy to be a reliable measure of human sex, but there are a variety of chromosomal abnormalities which make this ambiguous as well.  What sex is a person with XXY (two Xs makes them female, but the Y makes them male, surely?).  I recall being told in university that we weren’t allowed to count our chromosomes during laboratory practicals (formerly done by swabbing the inside of the cheek and then viewing the resulting contents under a microscope, called “karyotyping”) because if you had a class of 200 students then you were almost certainly going to have some ask “why do I not have the correct number?”.  Again, this is a non-trivial portion of the population.

Drosophila bifurca and a single sperm. They don't produce many...

Expanding the scope to non-humans animals, there are no external genitalia on a variety of species (including most birds and, possibly, dinosaurs), so it is no good just looking between an organism’s legs.  Root suggested that the sex cells themselves (eggs and sperm) might hold a clue.  For example, it is commonly thought that the sperm are small, motile (possessing flagella) and short lived.  However, some species of fruitfly (Drosophila) have sperm that are several times the length of their bodies, a number of species (such as the elephant fish) possess amoeboid sperm, and it is thought that ant queens store the still-viable sperm of their first matings for up to 20 years.  No luck there, then…

Finally, we came down to the real crux of Root’s research: the tiny, but significant, differences between males and females.  Root proposes two such differences, although these are both hypotheses that have yet to be fully explored.  The first is that female gametes (eggs) always undergo a process known as “meiosis” asymmetrically, whereas male gametes (sperm) undergo symmetric meiosis.  Basically, meiosis is the process by which cells with two sets of chromosomes divide so that they end up with one set of chromosomes. This enables them to combine with a complementary cell during sex to recombine their chromosomes up to the full complement.  Eggs tend to split and produce “polar bodies” – cells that are smaller and left to die.  This process occurs twice with the second phase of meiosis (after penetration by the sperm) emitting two polar bodies where the first only emits one.  The result is that you start off with one egg cell and end up with one egg cell, despite two stages of cell division.  In sperm, on the other hand, the cells divide symmetrically so that you start with a single sperm cell and end with four identical and equally-viable cells.  This is proposed to be the first of the two sex differences.

The second proposed difference involves the membrane that surrounds the nucleus of the sperm cell.  What is unique (and a little bit strange) about this membrane is that it does not have any pores (gaps) through which substances can pass.  Egg nuclear membranes do possess these pores.  In fact, when the sperm nucleus enters the egg cell, the sperm first has to shed the poreless membrane before it can interact with anything.  This is interesting because of the longevity of some sperm.  As mentioned above, ants store sperm for a long time, but pollen grains (essentially sperm-transport devices) also remain viable for long periods of time.  So how are these sperm remaining “alive” with a membrane that does not allow the passage of materials in and out of the nucleus?  Root thinks that these long-lived sperm systems might be an interesting testing ground for this hypothesis.

I know that Root’s research has attracted the attention of sociologists who are interested in the scientific basis for discrimination between genders or sexes.  He finished with a couple of implications of his research.  First of all, he noted that we are increasingly storing gametes (eggs and sperm) and if his research demonstrated that there was a difference between them, perhaps the “rights” accorded to the different gametes might differ?  More broadly, though, I think the context of his research gives us a greater appreciation of what it means to have a “sex” or “gender” (since the two are usually linked) and a greater understanding of the diversity of the world which too often is painted in black and white (or should that be “blue and pink”…?).

Root in full swing

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2 thoughts on “The difference between men and women

  1. That’s the interesting thing… The sex chromosomes (X and Y) have a degree of redundancy. If you are XX, the second X just switches off so you only have one chromosome doing all the work. Wikipedia has entries on some of the more common abnormalities:
    – XXY (“Klinefelter’s syndrome”) affects 1 in 600
    – XYY affects 1 in 1000
    – X (“Turner syndrome”) affects 1 in 2000-5000
    – XXX (Triple X syndrome) affects 1 in 1000
    – XXYY affects 1 in 18,000-40,000
    – XXXX has only been described a few dozen times,_XXXX
    …and a whole bunch of others (for more see

    These conditions vary in the degree of phenotypic expression. Most are indistinguishable from “normal” XX or “XY”, but some have characteristic morphological symptoms and some render the individual completely infertile. It is the autosomal (non-sex chromosomes, so the other 22 pairs) that are problematic and chromosomal abnormalities there lead to conditions like Down’s syndrome (extra 21st chromosome).

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