43

It's an interesting question and one that has been asked before. NPR did a story in 2013 on this topic, but their question was a bit more focused than just "why are so many black people good runners?" The observation that led to their story wasn't just that black people in general were over-represented among long-distance running medalists, but that ...


37

Short answer Shedding or reabsorbing the endometrial lining is energetically advantageous to the female.The advantage of shedding over re-absorption may be that sperm-born pathogens are removed from the uterus. A more parsimonious explanation, however, is that the endometrium in primates has developed into too large of a structure to be completely reabsorbed ...


34

Hair actually does have a limit to its growth. All hair cycles between periods where it grows, and when a new stand appears, which pushes the older, long hair out. Hairs that are generally shorter, like eyebrows or arm hairs, have a shorter growth period before a new hair pushes the old one out. The hair on your head actually grows much faster than many ...


25

Consumer water is not flavorless. Sources of flavor include (1) the chemical and microbial content, which is most influenced by geology and ecology; (2) chemicals added or removed during water treatment, and (3) inputs and reactions that occur during distribution and storage (Dietrich, 2006). Two examples of ecology-related flavors are geosmin and 2-...


23

An older answer that referred to the physiological feats of ancient humans, and why modern humans are wimps made me look up a couple of papers on running speeds a while ago. One of the examples used to support the statement that modern humans are "wimps" is a study of ancient fossilized footprints from Australia, which claim that the individuals making the ...


23

Short version The heart has the ability to beat independently of the brain as long as it has oxygen. The heart will eventually stop beating as all bodily systems begin to stop working shortly after brain death. Remember the heart can beat, but your diaphragm and lungs wont. hence the cardiac muscles undergo asphyxiation and die off. However, immediately ...


20

Hair grows from the follicle; there is no way for the follicle to determine if the hair tip is trimmed or not. This is unlike plant shoot/root growth that happens at the tip. Also there is no signaling from tip to follicle. Hair growth has four stages: Anagen (Initiation), Catagen, Telogen (resting) and Exogen (falling off). Initially the primary follicle ...


17

Short answer Between 62,000 and 63,500 feet (18,900 and 19,350 meters) blood begins to boil at body temperature. This altitude, referred to as the Armstrong limit, is generally considered to be the absolute limit compatible with life. At this point, humans cannot survive without pressurization measures. Background Atmospheric pressure drops at higher ...


12

Yes, bones too bleed if they get damaged (break or bruise). This is because bones are highly vascularised organs and breaking of bones will indeed rupture the blood vessels causing bleeding. Main artery which supplies blood to bone is nutrient artery , others are epiphyseal, metaphyseal and periosteal arteries. Skeletal system receives about 15.6% of cardiac ...


11

Take a look at Will Grover's answer here, I will cite the genetic diveristy explantion here, I think that sounds the most logical: Genetic Diversity This is my favorite answer, and the one that makes the most sense to me: Africans are more genetically diverse than other groups; in fact, they find that the further you are from Africa, generally the less ...


11

Because of the Orbicularis oris muscle, it's a complex of muscles in the lips that encircles the mouth, It forms the greater part of the substance of the lips, lying between the skin and the mucus membrane, and extending from the edge of each lip to its root.


10

Sydney Ringer showed in 1882 that when the heart, when separated from the body and immersed in lactated Ringer's solution, or even isotonic saline solution, will beat because it has its own pacemaker systems at the level of the Sinoatrial node and Atrioventricular node. This activity will continue until there is insufficient ATP to support it energetically. ...


10

Aspirine irreversibly inhibits the enzyme cyclooxygenase. This enzyme facilitates the reaction from arachidonic acid to prostaglandin G2/H2. The further reaction leads to the generation of Thromboxane A2 which is important for the activation and aggregation of platelets. See the figure (from here) for an overview: Thromboxane A2 usually stimulates the ...


10

Vitamin B12 (cobalamin) is a cofactor required by the enzymes methionine synthase (MTR) and methylmalonyl-CoA mutase (MUT). These are the only known enzymes that use B12 in humans, and are abundant in the liver. Since it is a cofactor, B12 is not consumed by any reactions, and hence there is no need to store large amounts of B12 beyond that bound to MTR and ...


8

Arterial Baroreceptors felling the pressure. Arterial blood pressure is normally regulated within a narrow range, with a mean arterial pressure typically ranging from 85 to 100 mmHg in adults. It is important to tightly control this pressure to ensure adequate blood flow to organs throughout the body. This is accomplished by negative feedback systems ...


8

Reticulocyte stage is when the ribosomes are still present and after that no new protein synthesis occurs. However RBCs have a lot of proteins and major proteins other than haemoglobin are cytoskeletal proteins and ion channels/pumps (In fact, cytoskeletal proteins are more abundant than haemoglobin). It is the Na+-K+-ATPase that consumes most ATP. As you ...


8

Sugar (be it sucrose, glucose, fructose or honey) does not have emetic properties in any concentration, unless there is a personal (and highly individual) psychological adverse reaction to sweet substances. Sugar is not a local gastric irritant (like dishwashing detergent, or syrup of ipecac, copper sulphate, zinc sulphate; yellow mercuric sulphate, ...


8

The issue is complicated. In general it depends on the specific spinal reflex and on the specific anaesthetic. But it seems that the modern general anaesthetics usually do NOT block monosynaptic spinal reflexes (such as knee-jerk). Here are two figures from Baars et al. 2009 that show that propofol and sevoflurane strongly inhibit withdrawal reflex (spinal ...


8

After we have eaten... the maximum blood supply is transferred towards the digestive system so that digestion is done, and therefore the brain to does not get adequate blood supply. Am I right about this? This is a very, very common myth, but it is a myth. Because blood flow and oxygen delivery to the brain is critical for survival, cerebral circulation is ...


8

I also found this hypothesis from a scientific paper which suggests that asian and white people have a lower center of gravity than black people. See the general explanation: Blacks tend to have longer limbs with smaller circumferences, meaning that their centers of gravity are higher compared to whites of the same height," said Adrian Bejan, Jones' co-...


8

You seem to have many misconceptions about how we see and how that relates to light. I'll address them one sentence at a time: Why are we able to differentiate between colored objects without the presence of light? Answer: the premise of the question is wrong: we aren't able to differentiate between colors without the presence of light, because we aren't ...


8

I will try to keep the answer as simple as possible, but feel free to point out if I make this too simple. Well, you are not alone with this observation. This is quite a common, but rather complex, phenomenon which controls our apetite and causes us to not feel hungry after waking up. The feeling of being hungry is under constant regulation by two ...


8

[D]o homeothermic and poikilothermic have the same meaning as endothermic and ectothermic respectively[?] No. Once you are referring to the source of the heat, while the other time you are referring to whether the internal temperature varies through time. Source of heat endo = inside exo = outside Variance in internal temperature Poikilo = varies homeo ...


8

This is an excellent question. You are on the right track with the random match idea. B-cells (as a group) develop receptors that bind every possible antigen and then get rid of the receptors that match antigens in our body. Some textbooks are a little more careful in their language, though, and say almost every possible antigen. See Alberts The ...


7

The eminent @JanDvorak has basically provided the full answer, but yes, it is possible. You can easily try this yourself, just lean off a bed and swallow something (small) and see what happens. Peristalsis in the esophagus is responsible for moving food down into the stomach. The big proof of this is that astronauts can eat when in space, when weightless. ...


7

Medical science has reached the point where it is able to consider performing uterine transplants in genetically female (cis-female) patients born without a uterus. In the MedlinePlus report, First Uterus Transplant Planned in U.S. doctors at The Cleveland Clinic have plans to perform the first uterus transplant in the US sometime in 2016. The article ...


7

Scanning various reviews it seems that everyone who mentions the possibility of a human chymosin refers to a single paper. So for example this 2014 review has a single reference to a human chymosin: Henschel et al. detected a protease in the gastric aspirates of newborn infants within 6–10 h postpartum that was not pepsin [62]. The electrophoretic ...


7

The endometrium changes throughout the menstrual cycle in response to hormones. During the first part of the cycle, the hormone estrogen is made by the ovaries. Estrogen causes the lining to grow and thicken to prepare the uterus for pregnancy. In the middle of the cycle, an egg is released from one of the ovaries (ovulation). Following ovulation, levels of ...


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