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May 15 - May 30, 2022
“Why” questions make for great exercises in hypothesis generation and experimental design.
Why do three-toed sloths come down from their trees to defecate? Sloths risk their lives to make a dung nursery for the moths on whom they depend for fertilizer to grow the algae they not only use as camo but also eat from their own fur for an extra shot of nutrition.
matters here is to understand that jaws and teeth have independent evolutionary origins.
Heterodont dentition, meaning having different types of teeth, is a hallmark of mammals—it allows mammals to eat a diet unparalleled in its diversity.
new-world monkeys (golden lion tamarins and howler monkeys are nice examples), ditched one of the incisors and one of the premolars from each quadrant to cut down the number of teeth to 36.
The other primate lineage, the old-world monkeys (like baboons and macaques) and the apes, also shed an incisor. In addition, they lost two of the premolars, leaving the standard adult complement of 32 teeth.
Given the option, all of the other great apes (chimpanzees, bonobos, gorillas, and orangutans) prefer cooked meat over raw.
The most convincing evidence suggests humans first made pots around 20,000 years ago in modern-day China.
the process of evolution does not plan for the future.
When vertebrates started living out of the water 375 million years ago, they already had eyes that had been around for 100 million years.
Tear ducts are drains at the inner edges of the eyes. Under normal conditions tears flow through the drains and down into the nasal cavity. The nasal cavity connects to the oral cavity and throat (as adventurous children discover creatively with a long piece of spaghetti), and most of those tears end up getting swallowed. At a total of around 300 milliliters (~10 oz) per day, it is not an insignificant amount of fluid. That is almost a Coke can full of tears every day.
Emotional tears are also a different blend from those used for run-of-the mill eye wetting or for reflex crying. The emotional, sniffling variety contain hormones like adrenocorticotropic hormone (ACTH) and prolactin. ACTH is a stress hormone, and prolactin is most commonly associated with the ability of female mammals to produce milk, though it has a wide range of functions in both sexes. No one knows exactly what those hormones are doing in tears, but don’t worry, the blink scientists are working on it.
Even before a few fish up and crawled out of the water, many of them had developed tetrachromatic (four-pigment) color vision.
Lungs emerged in very limited groups of fishes from outpocketing of the digestive system.
In other words, swim bladders and lungs are variants of the same basic structure.
crouching. Yes, crouching. The simple process of bending down to pick something up can lead to a tear in the meniscus. People with a meniscus tear often end up going under the knife because the body is lousy at self-repair of the knee, for reasons we’ll explore later in the chapter. The elderly are not the only victims of crouching injuries. Squatting was the “most frequent cause of a major meniscal tear in patients less than 30 years in the non-sporting injuries group.”
The incredible footprints preserved at the Laetoli site in Tanzania show that by 3.6 million years ago, the big toe was getting in line with the rest of the foot. The footprints unequivocally show the impression of the big toe next to the other digits, allowing for the push-off in the final part of the hominin gait, which is a quintessential feature of modern bipedalism.
I guess the girl just has a thing for cryptozoological animals descended from ungulates.
In a confusing bit of terminology, the natural curve is called lordosis and the condition where the curve arches too much is called...lordosis (or swayback). Too little lordosis = back pain. Too much lordosis = back pain.
In females, the lordotic lumbar wedging reaches up to include an additional vertebra. It might not seem like much, but the difference is significant. Having one more wedge-shaped vertebra allows females to mitigate the effects of shearing and stress caused by the extreme degree of lordotic curvature assumed during pregnancy.
instead of professing his love of big butts, it would have been more accurate for Sir Mix-a-Lot to say, “I like 45-degree lordotic curves and I don’t know why.”
Having taken place hundreds of millions of years ago, it is difficult to know exactly why notochords developed, but some scientists have suggested the notochord provided a rigid structure for the attachment of developing muscles.13 If you roll
the clock back far enough, some of the most primitive ocean organisms could swim only by ferociously beating their cilia and/or flagella, the microscopic hair-like projections found on nearly all cells. The development of a stiff beam along the long axis of an animal gave muscles something substantial to push against, which would have improved mobility.
As with the length of a period, the amount of blood lost during one cycle was highly variable. Light cycles were ones in which women bled fewer than 36.5 milliliters (ml). The medium tertile was for cycles between 36.5 and 72.5 ml of blood loss, and the heavy tertile was for cycles where there was more than 72.5 ml of blood lost. For the one-third of cycles defined as light, the average amount of blood lost was 15.2 ml.
Over roughly 40 years of menstruation, that adds up to 23.7 liters (more than six gallons) of blood lost over the course of the reproductive years. That is a staggering amount of blood loss. There are only five liters of blood in the average adult. A woman loses the equivalent of all the blood in her body almost five times over.
MOST MAMMALS DO NOT MENSTRUATE!!!!!! Most mammals reabsorb the excess blood and tissues, like a sponge soaking up extra fluid.
The most authoritative published list of mammals includes a total of 5,416 species.7 The only ones who menstruate are the 19 apes (including us), 132 old-world monkeys, half a dozen or so new-world monkeys (there are still gaps in the menstruation data for new-world monkeys), four species of bats, a rodent called the spiny mouse, and elephant shrews.
Mammals who experience spontaneous decidualization menstruate. Mammals with fetus-induced decidualization do not. In order
But if you’re a woman reading this, maybe it will help to know you are not alone in the animal kingdom. Somewhere out there in the wild there is a baboon, an elephant shrew, and a leaf-nosed bat having their period.
The title of Miller’s paper is “Ovulatory Cycle Effects on Tip Earnings by Lap Dancers: Economic Evidence for Human Estrus?”
When given 60 seconds to name as many words as they could starting with a given letter, women who were around their ovulatory window could name more words than they were able to in the period outside of their fertile time.
One testicle tends to hang lower than the other, and some have suggested this is because it allows for more exposed surface area for heat dispensation.14 If the boys are all snuggled up next to one another, it keeps the heat trapped, or so the thinking goes.
Tiny gorilla dicks and chimpanzee orgies aside, the important thing to remember here is that human males make unfathomable quantities of sperm—200 million sperm per ejaculate is a lot of swimmers.
Pregnancy resets a woman’s tolerance for what her body considers fresh. An aversion to meat is the most common type of aversion experienced by pregnant women, and the aversion is strongest during the first trimester.
Altricial infant animals are those with limited to no skills; infants who are more mobile and mature are called precocial. Those two terms are not discrete options but rather two ends of a spectrum.
Natural selection is not going to smooth the edges of our anatomical imperfections if those features play little to no role in who lives and who dies and how we choose our mates. In addition, there is no stopping new mutations from cropping up in the human genome. Some mutations do lead to improvements, but most genetic mutations either cause no effect or have a deleterious outcome. Whereas natural selection may have previously filtered out mutations with a negative impact on our anatomical features, in the more modern scenario many of those mutations persist within the genome.
