My colleague Paul Strode, a coauthor of this splendid book on evolution, once told me that, if you wanted to get a high-school student’s attention, just say “testicle.” The principle apparently works on New York Times reporters (and maybe physicists) as well.
Specifically, Steph Yin of the Times reports on a German team that studied the DNA of 71 mammals (by which I think he means 71 species) and found that testicular descent is an ancestral trait that was lost in elephants and certain other mammals. That is, elephants store their testicles internally, whereas most other mammals store theirs externally. It is uncertain precisely why testicles are generally stored external to the body, but it may have to do with the fact that sperm production is most efficient at temperatures lower than most mammals’ normal body temperatures. (I do not mean to be parochial, but you may find a short discussion of testicular descent and why it is poor design on pages 134-136 here. It was written almost entirely by Dr. Strode.)
Having internal testicles, that is, testicles that fail to descend, is called testicondy. In an e-mail to me, Dr. Strode hypothesized that eutherians (placental mammals) that exhibit testicondy might have slightly lower body temperatures than other eutherians. Wikipedia notes that aquatic mammals have special circulatory systems that cool their testicles. The normal body temperature of an elephant, however, is around 36 °C, or about one full degree Celsius lower than that of a human.
A remaining mystery, to me, at least, is what does the suffix “-condy” mean? I cannot immediately find it anywhere.