On the sixth human chromosome, there is a gene that codes for the glycoprotein leuteinizing hormone (LH), produced by the brain’s anterior pituitary gland. LH is less known for the role it plays in male testosterone production, and more on the minds of women who are trying to conceive. Its concentration peaks like a sole stalagmite only at the time of ovulation. When this happens, it stimulates the release of an egg from the ovary.
Unlike some other animals, humans cannot directly rely on their senses to detect the hormone. To see signs of its presence in urine, they have to use ovulation kits* which contain antibodies that bind to LH. A study of 155 cycles from 35 women revealed that LH surges mostly between midnight and early morning (37% between midnight and 4 AM, and 48% 4 and 8 AM)
Jacobson’s organ, a.k.a the vomeronasal organ, in snakes, giraffes and other animals is capable of detecting LH. In giraffes, the organ is at the base of its nasal cavity. The male takes the female’s urine into its mouth. If LH is detected, the signal travels directly to the brain’s amygdala, one of the centers of emotional learning. The excited giraffes subsequently engage in a slow neck-rubbing form of foreplay before the male mounts its mate.
The pair mating in the adjacent picture belongs to reticulated giraffes, one of four species that can be distinguished from their different spots. The latter do not only serve as camouflage against their background by breaking their overall outline. The blood vessels and sweat glands under each spot keep them cool from either the Sub-Saharan or southern African heat.
An estimated one million giraffes roamed the African continent in the 1700s. There are now only 110 000 due to deforestation, fragmentation of their habitats, war and poaching. A single 2000 pound giraffe yields up to 650 pounds (295 kg) of meat, but sometimes they are killed only for their tales, a status symbol in some cultures.
A giraffe’s stomach like that of the cow has four chambers. Leaves, which serve as their main food, enter the first chamber. Then coarse bits are regurgitated, chewed again and re-swallowed. Finally the cud passes through the three other chambers and through an 82-foot ( 25 meter) large intestine.
According to fossil evidence, 6-20 million years ago, ancestors of the giraffes had not yet evolved their characteristic long necks. In This View of Life, Stephen Jay Gould points out that Darwin finally used the giraffe’s neck in a discussion of natural selection in 1868, nine years after he explained the evolutionary mechanism. Each small increase in length, he said, would improve access to leaves. But he recognized that he was speculating about the supposed gradual elongation and necessary accompanying changes in anatomy. Without a knowledge of genetics, Darwin had not discounted Lamarck’s version, unlike the story told in science magazines and high school textbooks.
*Some tests also measure another hormone — estrone-3-glucuronide (E3G)
Detection of ovulation, a review of currently available methods https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5689497/
Histological features of the vomeronasal organ in the giraffe, Giraffa camelopardalis. https://www.ncbi.nlm.nih.gov/pubmed/28094892
Giraffes. National Geographic. October 2019
Gould, Stephen Jay. The Tallest Tale. Natural History. May 1996.