I've just started browsing through a book with the promising title, Quirks of human anatomy: an evo-devo look at the human body. (Held, 2009). (The Science librarian does a great job of sifting through new titles & running them past the various departments in our Faculty to see what people would like to see added to the shelves.) Held says that he wrote the book as
a kind of amusement park. Its thematic 'pretend game' is to insepct each body part through the eyes of an alien visitor who asks, "why is it this way and not that?"
Very early in the book there's an image of vertebrate 'morphospace', which moves from the familiar to the seriously strange, and from reality to things - like Dumbo & ET - that can be conceived of but which are unlikely to exist due to various physical constraints. Cool!
As I said, I've only begun dipping into Quirks, but I've already come across a couple of examples that I'll probably use in class. One is of a set of twins, born in France in 1844, who seemed on the basis of various tests (done when they were 17) to be monozygotic - yet one child was a boy & the other, a girl. Seems impossible... When cells from each twin were karyotyped, the boy was (as expected) XY i.e. he had 23 pairs of chromosomes, 22 of them 'somatic' & the 23rd pair the typical 'sex' chromosomes of a male mammal. His sister, however, was XO: 22 pairs of somatic chromosomes & just a single X, characteristic of Turner's syndrome.
How could this be? The original zygote must have been XY. Presumably a Y chromosome was lost from one or some of the embryo's cells before it split to form 2 embryos, with all the XO cells cohering & thus giving rise to the female twin.
Just as strange is the story of one Daniel Burghammer, who'd been married for 7 years when, in 1601 he gave birth to a child (doubtless to the extreme confusion of his poor wife!). According to the contemporary account, Daniel "was half man & half woman" & had at one point slept with a another man, an act which resulted in his pregnancy. You might think that this is just a fantastical tale, were it not for another example reported in the New England Journal of Medicine in 2004: an infant who
had a penis (with hypospadias) and scrotally enclosed testis... on the right, but a hemiuterus, oviduct, and ovary internally on the left.
Where this gets really weird is that cells on the 'male side' of this child were all XY, but those on the 'female side' were XX. Held suggests that the child may be a chimera, where 2 sperm fertilised 2 eggs, but the resulting zygotes then fused to produce a single embryo. But as he says, without DNA analysis we'll never really know.
I am really looking forward to my bedtime reading for the next few days!. And this will certainly enliven my lectures on reproduction!
L.L.Held, Jr. (2009) Quirks of human anatomy: an evol-devo look at the human body. Cambridge University Press ISBN 978-0-521-73233-8