35
votes
4answers
108k views

What's the maximum and minimum temperature a human can survive?

This is a question that has been in my mind since I was a kid. I'm not a doctor, nor even a biology student, just a curious person. What is the minimum and maximum temperature a human body can stand ...
23
votes
4answers
976 views

How many times did endosymbiosis occur?

According to the endosymbiont theory, mitochondria and chloroplasts originated as bacteria which were engulfed by larger cells. How many times is it estimated that this occurred in the past? Are there ...
21
votes
5answers
10k views

Why do the two hemispheres of the brain control the opposite sides of the body?

Why does the left hemisphere control the right and the right hemisphere control the left? I googled it but didn't find a good answer regarding this. Could someone explain? Does this adaptation help ...
20
votes
3answers
457 views

Good source that explains the evolution of single-celled organisms “from scratch”

Are there any books or sites that detail, step-by-step, the evolution of the first single-celled organisms (bacteria, archaea) from a Miller-Urey-like beginning? That is, assumes only amino acids, ...
15
votes
4answers
4k views

Height and natural selection in humans?

I watched the documentary "Evolve" recently and in the segment on "size" Scott V. Edwards, Harvard evolutionary biologist mentioned the idea that humans might evolve to be 7' tall in 'hundreds of ...
14
votes
4answers
3k views

If body temperature is 37°C (98.6°F), why are most people more comfortable at around 21°C (70°F)?

It may be different for other people, but for me, anything above 32°C (90°F) is very uncomfortable, and my body is inclined to seek cooler temperatures. But I would think that at 32°C, the body would ...
14
votes
1answer
2k views

Why does hair turn grey or white, and why does it happen later for some?

The question is pretty simple: what is happening molecularly when hair turns grey or white? I would imagine that it is due to the lack of a particular compound. I'm also interested in why some ...
14
votes
4answers
99k views

Why is DNA replication performed in the 5' to 3' direction?

DNA replication goes in the 5' to 3' direction because DNA polymerase acts on the 3'-OH of the existing strand for adding free nucleotides. Is there any biochemical reason why all organisms evolved to ...
13
votes
3answers
5k views

When has an organism evolved enough to be called a new species?

Imagine that we take a population of horses, split them in half and place them in completely different environments. The two species will evolve separate from each other and because the environment is ...
12
votes
3answers
2k views

What does irregular heartbeat mean in simple language?

I bought a blood pressure monitor (A&D UA-851) which has the option to measure irregular heartbeat. I do understand what 'irregular' means, but why do irregular heartbeats happen and what are ...
11
votes
3answers
17k views

Do apes and humans share 99% of DNA or 99% of genes? What is the difference?

I made an answer on the Scifi.SE that can be read here. It is about how the characters in the story Jurassic Park might have gotten DNA for all the species shown. In my answer, I said this: Apes ...
8
votes
1answer
2k views

why is DNA antiparallel? Can it be parallel?

My biology textbook mentions that DNA is antiparallel and it got me wondering... Can DNA be parallel? What would happen if it was parallel? could DNA still replicate right?
8
votes
2answers
473 views

Do immortal organisms exist?

Do organisms exist that are able to live indefinitely if they are not killed by external factors? Under external factors I would consider things like predators and natural disaster but not illness by ...
7
votes
2answers
274 views

How does Natural Selection shape Genetic Variation?

Background Importance of the additive genetic variance As stated here, the fundamental theorem of Natural Selection (NS) by Fisher says: The rate of increase in the mean fitness of any organism ...
6
votes
1answer
2k views

Are sensory receptors neurons?

Background There are many receptor types in the body, with various functions and various mechanisms of transduction. Receptor cells are considered to be part of the peripheral nervous system, as they ...
6
votes
1answer
175 views

The origin of molecular machines

DNA holds genetic information and holds the key to the evolution of living organisms. Transcription and translation mechanisms enable living cells to process information encoded in DNA. To that end, ...
5
votes
1answer
653 views

Is there any size limit to the amount of information a human (or other) brain can hold

Im not sure how this would ever be tested but is there a limit to how much the brain can 'hold' before it reaches capacity ? I guess this could also be interpreted in terms of memory, as how well ...
3
votes
1answer
142 views

What in neurons and their connections changes during the process of learning?

I'm not sure if this question belongs more in physics or biology (or maybe even computer science)... but biology seemed to fit more. What changes in the state of our brains when we learn things? ...
3
votes
2answers
1k views

What are gram negative and positive bacteria?

I've just finished a course of double antibiotics for Helicobacter pylori in my stomach. I looked up H. pylori and found that it was a gram-negative bacterium. I looked up gram-negative and didn't ...
18
votes
3answers
511 views

Are human fetuses more likely to be male? [duplicate]

Question: From a physiological point of view, when sex is determined in a human fetus, is it equally likely to be male or female? Studies in this area typically measure age at birth, where the data ...
17
votes
3answers
4k views

Are humans the only animal that requires “clean water”?

I've seen a number of animals - dogs, cats, squirrels, ducks and geese, etc drink from puddles, some of them were muddy, others had green flora growing under water. Same goes for lakes and rivers. A ...
17
votes
2answers
45k views

How many human cells are there in our body, on average?

How many human cells are there in our body, on average? Wikipedia says 1013: Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in ...
17
votes
3answers
451 views

Why would diffusion be faster across a non-specialised tissue?

The standard protocol for a person experiencing chest pains is to chew a 300mg aspirin tablet, the argument being that chewing rather than swallowing the tablet results in the aspirin entering the ...
15
votes
3answers
1k views

Why do some trees have a life span, while some don't?

I have heard that there is no limit on the growth of trees, but then why do some trees, such as boxelders and poplars, tend to live shorter than redwoods, for example? Some advertisements for improved ...
14
votes
5answers
458 views

Is it the case that all changes in phenotype during life are not inheritable?

This came up in a talk with a friend. I wanted to clear this doubt. I've read about it before and did again after her remark (my thoughts didn't change: her concept is Lamarck's, not Darwin's), but ...
11
votes
1answer
12k views

Why is ATP the preferred choice for energy carriers?

Why is ATP the most prevalent form of chemical energy storage and utilization in most cells?
11
votes
2answers
2k views

Why does strenous exercise cause vision of “lights”?

I had a hard climb a week ago. I got so tired then any time I closed my eyes I saw these lights inside my head. I see these lights almost every time that I run fast or some thing like that. What are ...
10
votes
3answers
1k views

Why did humans become bipedal?

Somewhere in evolutionary history homo started walking upright and became bipedal. You hear these hypotheses that, by walking upright, they could see better across the grassy savannas to escape ...
10
votes
1answer
315 views

Is it a limitation of the eyes, or the brain, that we can't see a moving bullet?

Are the photoreceptors in our eyes not fast enough to register the fast moving bullet, or is the brain not powerful enough to make sense of something happening that fast?
9
votes
1answer
128 views

What are the survival limitations of alcohol?

This question was inspired by watching one of the Pirates of the Caribbean movies; particularly where Jack Sparrow allegedly survives on a desert island by finding an unlimited supply of rum. I've ...
9
votes
3answers
7k views

Why can all animals swim in water without learning to swim but humans cannot?

I had a question since I was a child. I was always curious about the fact that all animals can swim in water. They don't need any training or to learn swimming. But humans need to learn to swim. Why ? ...
9
votes
2answers
171 views

What role does a protein's size have on protein-protein interactions?

Protein-protein interactions are when two or more proteins bind together, possibly for some important biological function. Recently, I'm starting to look more into proteins, and in particular, ...
8
votes
3answers
7k views

Why doesn't recombination occur in male Drosophila?

"Males do not show meiotic recombination, facilitating genetic studies." For a while I have known that this phenomenon occurs, this quote comes from the Wikipedia page on Drosophila melanogaster, ...
8
votes
1answer
1k views

Does extracted DNA degrade after a certain time period?

For direct use as template in PCR runs. Chelex 100 5-10% w/v extraction. Without listing the whole protocol, in the end the supernate is decanted off and then stored at 4°C. I was under the impression ...
8
votes
2answers
1k views

How does an inhibitory synapse communicate to the cell body of a neuron?

I picture a neuron as having multiple trees of dendrites attached to the cell body with a single axon leaving the cell body. I believe the cell body near the axon root makes the decision to fire or ...
7
votes
3answers
135 views

How is genetic speciation defined?

What determines speciation at a molecular level? At what point does a scientist determine two lineages are different enough to be considered separate species? Does it have a margin of error?
7
votes
2answers
431 views

Why sleep? No, actually, why wake?

I was just reading the sleep threads, and I wondered, why is the body so constructed so that sleep is necessary? (Is it just a design error?) But then, how do things come to be awake at all? How did ...
7
votes
2answers
142 views

Why is there no way to remove an immune response?

We've known for a long time now how to "add a new entry to the database," as it were, of immune responses. It's called vaccination, and it's been one of the greatest success stories in the history of ...
7
votes
1answer
5k views

What are the advantages and disadvantages of being ambidextrous?

Most of us have one dominant hand. We find it nigh on impossible to do very delicate or dextrous activities with our other-hand. This seems like an apparent weakness, and a rather odd one when you ...
7
votes
4answers
714 views

Suitable introductory book on Bioinformatics for a computer scientist?

Do you have any suggestions on a suitable introductory text on bioinformatics for a computer scientist? Any recommendations with pros and cons of different books would be appreciated. I'm mainly ...
6
votes
1answer
1k views

Why does a light object appear lighter in your peripheral vision when it's dark?

So, I am not sure I can reproduce it via images, but the steps are: 1) At night, open a window and have a look at the surface of the earth 2) Suppose there's an object that reflects a tiny amount of ...
5
votes
1answer
277 views

How does a fetus retain a blood group different from its mother?

It's a well-established fact that blood group is decided by genotype. But, when a new child starts its journey in the womb, the mother's blood (along with it's agglutinins and agglutinogens) flows ...
5
votes
2answers
533 views

How long can the brain survive during ongoing cardiac arrest?

There was this interesting discussion on CPR and defib in response to the question "Why can't we defibrillate the heart within 1 minute after ventricular fibrillation by electroshock?". Now I was ...
5
votes
1answer
340 views

What is a Mitochondrial Eve and Y-chromosomal Adam

I've read this question: What kind of event would cause the current Mitochondrial Eve to be replaced by a new one? And the values in Wikipedia about Mitochondrial Eve and Y-chromosomal Adam and I am ...
4
votes
1answer
124 views

What effects does being cryogenically frozen have on a person's body? [closed]

I'm wondering what effects are known to happen to a person's cells when a person is cryogenically frozen, especially those that need to be overcome in order to "bring them back to life." From a ...
4
votes
2answers
540 views

How does the brain know where a signal came from? What is the addressing system

I am an electronic engineer so I am thinking about this from an electronics outlook. How does the addressing system work, As I see it, the nervous system is small parallel branches attached to larger ...
4
votes
2answers
271 views

Book recommendations for algorithms used in evolutionary biology

Do you have recommendations for a book that presents the different algorithm used in theoretical evolutionary biology? I don't mean evolutionary or genetic algorithms (otherwise this question would ...
4
votes
3answers
1k views

Chromosome 2 fusion?

I read this article by Jeffrey Tomkins and Jerry Bergman claiming to debunk chromosome 2 fusion. Is there anything wrong with these conclusions? " 1.The reputed fusion site is located in a ...
3
votes
1answer
279 views

Elevated position effect on recovery times from upper respiratory infections at rest?

In nursing school, they advice for people with upper respiratory infections to be in a slightly elevated position at the head region when sleeping. My intuition of the reason is that the lymphatic ...
3
votes
1answer
276 views

Ventral stream pathway and architecture proposed by Poggio's group

Please can you give me a very brief explanation about all functions in the ventral stream architecture summarized in this figure: This figure is from Serre et al.'s A quantitative theory of ...

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