Valentine Pontifex

I am not talking about basketballs, footballs, etc...


Heat could flip sex switch

I don't know if I believe it, but it sort of makes sense. It will be interesting to see where the evidence goes on this one.

Dr.GH

A popular song in the late 1700s was
"Do your balls hang low?
Do they wobble to and fro?
Can you tie them in a knot?
Can you tie them in a bow?
Can you throw them o'r your shoulder
like a Continental solider?

Do your balls hang low?"


Male mammals tend to have pendulous testicles, while avian males do not. Both are warm blooded, and so the temerature argument seems to be incomplete. I seem to recall a similar thermal hypothesis from the 1960s, but more related to sperm motility rather than sex selection.

Nic Tamzek

Gee, the version I learned in summer camp was "do your ears hang low".

:-)

The Lone Ranger

Birds have air sacs (basically, extensions of the respiratory system) which circulate air through the body. It has often been suggested that one of their fuctions is to cool the testes.

Cheers,

Michael

Dr.GH

Yep. But councilors, in an unbroken oral tradition back to Valley Forge, sang the true original on our single 1/2 hour of free time per week!



There was a rumor that the Girls camp councilors sang a heretical version:

"Do your boobs hang low?
... "

But, I now realize they were too young to have understood the true implications.

RufusAtticus

Oh good. I thought this thread was on the evolution of bulls.

Undercurrent

I'd heard it as being related to the mamalian gait. With the legs brought under the body, the muscles near to the gonads are used more when running. That creates heat and pressure waves that are what is not conducive to sperm creation.

It could be argued that at least for flying birds, where the need to run long and hard is ameliorated by the ability to fly, the interference from those muscles is not as great. Doesn't say much about Ostriches, though.

But if the "temperature control for gender" hypothesis bears out, it will be very insightful as to how the whole thing evolved. Seeing data for the specific biochemical changes in evolution is, IMO, a lot more deeply satistfying and less subjective than putting fossils in order.

Oolon Colluphid

Now that is weird (from a creationist perspective especially). Because it doesn't seem to matter for ovaries.

Oolon

Non-praying Mantis

Modern day reptiles are called "cold-blooded," but this is a misnomer. The blood temperature of lizards is often high, close to that of mammals! However, lizards have to maintain the high temperature through other means such as sunbathing, instead of increasing their metabolisms like "warm-blooded" animals do. The correct name for "cold-blooded" is ectotherm - which means having an external source of body heat, compared to endotherm - which means is capable of using controlled metabolism to increase internal heat which maintains body temperature.

So reptiles have high body temperatures (at least some of the time) and internal testicles! Figure that one out.

NPM

Wounded King

For many reptiles the sex is determined based on the temperature that the egg is kept at before hatching, by which I mean the fertilised egg not the ovum. The criteria for sexual development simply arent the same, so if that really is why humans etc. have them on the outside then this would not argue against it.

Here is a site mentioning temperature dependent sex determination in reptiles.