Biology pertaining to humans.

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The genetic and physiological origins of laughter?

This Wikipedia article defines laughter in many terms, such as... "a visual expression of happiness, or an inward feeling of joy" and "a part of human behavior regulated by the brain, ...
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1answer
500 views

Is it true that newborn babies don't produce tears while crying? Why?

Well, I was just going through an article on eye, where in fun facts it was mentioned that newly born (for initial 1 to 3 months) babies do not produce tear while crying. Actually, I have found this ...
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325 views

How did the human brain evolve?

A common question posed is, "how did the eye evolve?", because the eye is so complex. However, this has been answered rather clearly and there are several examples around the world of animals in ...
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1answer
169 views

Why is the Patellar reflex not triggered when the tendon is extended slowly?

I have been previously told that the Patellar reflex (knee-jerk-reaction) exists to prevent the hyper-extension of the patellar tendon. Yet if the impact to the tendon is delivered slowly - i.e. by ...
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637 views

Is there an evolutionary advantage to crying when sad?

It seems as though the act of crying when sad does nothing to relieve that sadness. Is there an advantage to crying from an evolutionary perspective, or is it the end result of a different process? ...
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2answers
2k views

Will humans and animals be harmed by frequencies outside their hearing range?

The human ear (for example) is sensitive to frequencies from 20Hz to 20kHz. Any sound beyond that limit would not be heard by us naturally. Will it harm us (effect our ability to hear) when we hear ...
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3answers
955 views

What happens to dextrorotatory amino acids in humans?

As indicated by this question, most of the amino acids in the human body have the L-chirality. As enzymes also have handedness, what happens to the D-amino acids that end up within the human body? Are ...
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1answer
194 views

In which order did the cells of the immune system evolve?

Thinking about how complex the interactions between different types of immune system cells (T-helpers, T-Killers, Phagocytes, B-Cells etc.) are, it's fascinating how they all combine to get the ...
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128 views

Does muscle growth trigger angiogenesis?

So heavier people generally have more blood than lighter people (this is why heavier people generally need to take higher doses of medication for the same effect of medication). They also have more ...
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129 views

Relationship between our microbiome and personalized nutrition

Recently, it has been asked whether there are 'metabolic types' between humans that can benefit from a sort of personalized nutrition. One answer suggested that one discerning factor could be the ...
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220 views

Is there such thing as a generic “metabolic type”?

A while ago I picked up a book called "Eat right for your metabolic type". The book discussed the effects of the endocrine system on the overall shape and the speed of metabolism. The book outlined ...
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1answer
535 views

What happens to a human body once a sugary snack is consumed?

I'm looking to understand the effects of sugary snacks and/or drinks on a human body. I'm particularly interested in the timing of the ingestion versus various hormonal levels that may be circadian in ...
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193 views

What can the timing of human urination tell about the human's physical condition and circadian rhythms?

I've noticed a peculiar phenomenon. A subject drinks 400 ml of water, then observes time until the urge to urinate is felt. The time is 15 minutes. The subject releases water. 14 minutes later another ...
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4answers
4k views

How many genes do we share with our mother?

Somewhere I have read we share more than 99% of our genes with every other other person and 98% of our genes with chimpanzees. What does this mean? Don't we share 50% of our genes with our mother and ...
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176 views

During famine, does the human body do anything to prioritize which organs receive nutrients?

When food is scarce, the body slows its metabolism. Are there any other systems or processes that encourage prioritization of organs?
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196 views

What is the biology behind a skin “mole”?

Are the dark marks aka "moles" on our skin a patch of dead cells? If so, why is it not cleared over time? In a (probably) similar vein, why do scar marks from injuries remain long after new cells ...
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130 views

How was the guided daily amount (GDA) calculated?

We are constantly shown nutritional information on food packaging stating this food contains "x" amount of your guided daily amount. A linked to the values is here. How were these values calculated? ...
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471 views

When to measure resting heart rate and blood pressure for following day-to-day trend?

I'd like monitor my resting heart rate and blood pressure to see how they are affected by regular cardiovascular training and other events in life. When should I take the measurements in order to ...
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11k views

Possible? When a pregnant woman suffers an organ damage, fetus would send stem cells to the damage organ to help repair it?

I am quite sure that there is this blood-placental barrier between the mother and the baby so that nothing (except a type of antibody) can pass through it. But I remember reading somewhere that when ...
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218 views

Weighing 2 vertical halves of the human body

I had this thought while bathing: Assume a perfectly developed physical human body and anatomy in terms of size, dimensions and proportions. In theory, if I cut the body vertically into two exact ...
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2answers
586 views

Do probiotics survive digestion?

Pretty much this. I've been wondering if any of the yogourt and other "health" foods containing living probiotic cultures survive digestion to populate our intestines? If so, is there peer-reviewed ...
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2answers
2k views

What actually happens when my leg 'falls asleep'?

Most people have experienced the temporary loss of feeling and tingling in their leg resulting from sitting in an abnormal position for a short while. Usually you get a loss of feeling in your leg ...
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2answers
420 views

Why is rabies incurable?

I'm still not sure about the mechanics that lead to rabies being incurable. I know that it can be treated before any symptoms show up, but why is it that once symptoms show the person is a dead man ...
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636 views

Why do people say that trans fatty acids are bad for your health?

I've heard from several sources that trans FAs are bad for you and their consumption will lead to cardiac problems, and that they are indigestible. But I also learned from biochemistry that they are ...
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446 views

What causes a 'stuffy' or 'runny' nose when you have a cold?

When humans get the common cold, a common symptom is a stuffy or runny nose. Is that the body's immune response or is that the virus's doing?
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2answers
364 views

Is the 'fluttering feeling' when under stress neurological or physical?

I'm sure that everyone is familiar with the sensation commonly known as "butterflies in the stomach". It is commonly experienced during periods of anxiety or stress (e.g. before high stakes job ...
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535 views

Why are goosebumps so ineffective at keeping us warm?

If the purpose of "goosebumps" is to keep us warm, why is it so ineffective? Or are the changes subtle, but important?
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289 views

Where do the bacteria within the vagina originate from?

I understand that it's feasible the bacteria within the gastrointestinal tract originate from the food we eat and air we breath, but where does this population of microbes originate from?
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Origin, or source, of rhesus negative in human blood

This is my first post here, so please be gentle. I recently learned that I have Rh- blood (I'm A-), and was idly looking into blood types on Wikipedia. I was surprised to find that relatively few ...
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410 views

What conditions are necessary for HPL (human pancreatic lipase) to activate?

What conditions are necessary for human pancreatic lipase to activate? Is there an optimal temperature or pH? How quickly does it take effect?
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524 views

Does testosterone increase female sexual behavior?

According to my lecture notes testosterone generally increases sexual behavior. Given that it's generally thought to be the male hormone I'm not quite sure whether they mean that it also increases ...
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2answers
127 views

Does age affect the frequency of flatus?

Is there any relation between age and the frequency of flatus? I often have this feeling that older people f*** more often than younger ones. Is this feeling scientifically correct?
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3answers
1k views

How does the human body metabolize gasoline?

A Chinese man has been drinking gasoline to relieve his pain for 25 years. How does the human body metabolize gasoline? Also, what are the side-affects to gasoline?
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2k views

What is the role of acetylcholine in blood pressure regulation?

What is the role of acetylcholine in the cardiac cycle and in blood pressure regulation?
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106 views

What is the number of cells in a line of a fingerprint?

I have been reading a little about the size of cells and was curious as to how small they really were. I have noticed that on my finger, the outlines of the fingerprint are made up of thin lines. In ...
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191 views

What causes light to be brighter in the corner of the eyes?

I have noticed when in a dark room light and color seem to be brighter and more intense in the corner of my eyes. For example the light that comes from my digital clock seems like a dark pink when I ...
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2answers
304 views

Does arterial blood always flow away from the heart?

Is there a negative net flow of blood in human arteries at any point of the cardiac cycle? I realise that blood flow can be turbulent, e.g. in the aorta or around stenotic arteries, but then the ...
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4answers
3k views

Do white Australians have a distinct look?

Background I've heard from many people working in tourism or similar industries that, white Australians can be recognized as Australian solely by their facial features. Being Australian myself I've ...
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1k views

What influences the timing of human bowel movements in the morning?

I'm trying to understand if the timing of human bowel movements in the morning is associated with the circadian rhythm, and can thus be used to make predictions about the circadian rhythm. What ...
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1answer
238 views

Human sleep cycles and dream times, what influences the timing and intensity? Sleep history included

I'm doing sleep and dreams research and have developed an iPhone application to help me track my bedtime, rise time, sleep onset and also mark dreams. The app also monitors overall activity overnight ...
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1answer
344 views

Which human body hormonal systems exhibit 24 hour diurnal cyclical activity?

I'm researching the possible connection between the dream content and the activity of various organ or hormonal systems within the human body. I'm looking for information on biological cycles within ...
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465 views

What forms the human amniotic sac?

I am trying to understand the formation of embryonic disc for human and chick so the following question is related to here about formation of embryonic disc. I had thought that the amniotic sac forms ...
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3answers
980 views

Fetal development, gastrulation and embryonic disc

I am completely confused by the images circulating on the internet of human gastrulation. First, lets see how it happens in deuterostomes. This image depicts the process: (image is from Wikipedia) ...
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1answer
583 views

Do eye muscles relax when you close your eyes?

I wonder whether the eyes muscle relax when you close them. Common knowledge told us the eyes muscle get tense when you stare at nearby object. If you close your eyes, you eye lids have 0 distance ...
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3answers
5k views

What causes fingerprints to form and why is the pattern formed unique?

I've found research that suggests that the reason we develop fingerprints is because they aid us with feeling surfaces (Scheibert, et al. 2008) and not to increase friction and help with the gripping ...
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4answers
1k views

Can two humans with 44 chromosomes produce viable offspring?

It is known that there are very few individuals having 44 chromosomes, not the usual 46 chromosomes. One example is a male in China: the first article, the second article. The other is a female in ...
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3answers
11k views

Why do mammalian red blood cells lack a nucleus?

How did the red blood cell in humans get to lose its nucleus (and other organelles)? Does the bone marrow just not put the nucleus in, or is it stripped out at some stage in the construction of the ...
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2answers
4k views

Mitosis in human body

I've heard that stomach lining has the fastest reproducing cells and the brain has the slowest. Where in the human body does mitosis occur and at what rates do these cell reproduce? Is there a chart ...
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1answer
330 views

Why do people look different after a long sleep?

What happens during a long sleep that makes people look odd when they have just woken up? Why doesn't the same phenomenon occur in the case of a person who lies down for an extended period of time, ...
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1answer
2k views

What are differences between formation of embryonic disc in chick and mammal embryo?

Exam question which got lowest average points in my university: 1/5 average. No markscheme available so my attempt below. I assume that embryonic disk prefers to germ disk such that Formation prefers ...