12/10/2023 0 Comments Shaved chimpanzee storysapiens have 10 times more eccrine glands than chimpanzees, but similar hair follicle density. ![]() The resulting 2018 Journal of Human Evolution paper showed H. The team also compared human and primate skin by counting follicles and glands in biopsies from cadavers. The discovery pointed to a potential genetic link between fur loss and sweat gland gain in mammals. The team found that less hairy mice also had more eccrine glands, and that the gene En1 appeared to be responsible for increasing sweat gland development while reducing hair production. The researchers began by comparing DNA from mouse breeds that grow differing amounts of hair on their paws - previous research had suggested that some genes may play a role in both hair and sweat gland development. We didn’t know what to look for,” she says. “We had no idea where to look in the genome. However, finding these genetic variants wasn’t easy, says Yana Kamberov, who joined the research team while at Harvard and now leads it at the University of Pennsylvania. Geneticists have the technology to see how evolutionary change happened at a basic biological level - in this case, how minor alterations to the DNA code shared by all primates could lead to uniquely human sweat and skin. So Lieberman and other Harvard scientists launched a project to find the cause of human fur loss in our genes. The scenarios are plausible, but impossible to test with fossils, the traditional source of evidence for understanding human evolution: No early hominin skin or hair has survived the ages. The animals would eventually overheat, allowing sweaty hominins to nab their meal. Lieberman hypothesizes that roughly 2 million years ago, Homo erectus pursued prey by trekking and endurance running through the hottest hours of the day. ![]() (Credit: Jay Smith/Discover)Īlternatively, perspiration-prone skin may have been advantageous later in our origin story, when hominins became hunters. We also have 10 times more eccrine glands, the source of watery sweat. Chimps have more oil-secreting apocrine glands ours occur only in a few areas of the body. Humans have about as much hair as chimps, but ours isn’t as thick. But, if they were efficient at reducing heat through sweating, these small, two-legged hominins could have stayed safe by foraging during midday heat, when most carnivores rest. Since two legs are slower than four, “we became easy pickings for any carnivore,” says Lieberman. The first scenario places fur loss within a few million years of the origins of bipedalism, when our ancestors were merely 3 to 4 feet tall, with chimpanzee-sized brains. And this likely explains why hominins kept hair on their heads. But bipeds could forgo this protection because only their scalps are exposed to direct rays. Fur usually shields mammals from damaging solar radiation. Both assume the changes occurred after hominins - the evolutionary branch of apes leading to humans - began walking upright and traded tropical forests for open, sunnier habitats, some 7 million years ago. Lieberman has proposed two scenarios for when and why fur was sacrificed for sweat. ![]() But the details on when and how are still patchy. Researchers think fur loss coincided with eccrine gland gain in our evolutionary story, as paired adaptations for better sweating. Thick fur impedes this process bare skin promotes it. Sweat cools the body through evaporation, drawing heat away from the skin. “Humans have just gone wild with those glands,” says Lieberman. Chimp skin comprises roughly two eccrine per one apocrine, but ours is almost all eccrine. The disparity is partially explained by relative abundances of two types of sweat glands: eccrine, the source of watery sweat exuded through pores, and apocrine, which secrete viscous liquid from within hair roots. On a hot day, an average Joe can sweat 12 liters maximum rates for humans are over four times that of chimpanzees. Homo sapiens also stand out as the most perspiring primate. “Humans can dump heat … whereas other mammals, when you chase them, overheat,” says Harvard University evolutionary biologist Daniel Lieberman. Reduced body hair enhanced the cooling capacity of sweat, a crucial adaptation in our ancestors’ hot, savanna-like environments. They contend fur loss was not for sex, but survival - specifically, survival of the sweatiest.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |