All Questions

268
votes
3answers
237k views

Why do I only breathe out of one nostril?

I was just sitting with my hand next to my nose and I realized that air was only coming out of the right nostril. Why is that? I would think I would use both, it seems much more efficient. Have I ...
176
votes
3answers
29k views

Why are so few foods blue?

Although blue foods exist, they're rare enough compared to other foods for food preparers to use blue plasters as a convention. The natural colour of a given food is due to pigments that have some ...
144
votes
2answers
5k views

How many times did terrestrial life emerge from the ocean?

Evolution is often mistakenly depicted as linear in popular culture. One main feature of this depiction in popular culture, but even in science popularisation, is that some ocean-dwelling animal sheds ...
143
votes
7answers
14k views

Does DNA have the equivalent of IF-statements, WHILE loops, or function calls? How about GOTO?

Does DNA have anything like IF-statements, GOTO-jumps, or WHILE loops? In software development, these constructs have the following functions: IF-statements: An IF statement executes the code in a ...
124
votes
1answer
14k views

Do bacteria die of old age?

I know that the cells of mammals at least stop dividing when they are old, and then die a programmed cell death. Then other cells have to replace them. But in a bacterial colony, each cell ...
118
votes
4answers
5k views

Is there a reason why human eyesight and plants make use of the same wavelength of light?

The accepted range for the wavelengths of light that the human eye can detect is roughly between 400nm and 700nm. Is it a co-incidence that these wavelengths are identical to those in the ...
110
votes
3answers
105k views

Why is thymine rather than uracil used in DNA?

What is the advantage gained by the substitution of thymine for uracil in DNA? I have read previously that it is due to thymine being "better protected" and therefore more suited to the storage role ...
104
votes
3answers
23k views

Are male and female brains physically different from birth?

Male and female brains are wired differently according to this article: Maps of neural circuitry showed that on average women's brains were highly connected across the left and right hemispheres, ...
101
votes
8answers
17k views

Why do plants have green leaves and not red?

I know plants are green due to chlorophyll. Surely it would be more beneficial for plants to be red than green as by being green they reflect green light and do not absorb it even though green light ...
95
votes
2answers
11k views

Can HIV be transmitted via mosquitos?

It is known that HIV is usually transmitted by direct blood or body fluid contact between an infected individual and a healthy person (like blood transfusion or needle sharing): Suppose a mosquito ...
94
votes
3answers
10k views

What is the effect of non-vaccinated people on vaccinated people?

Many times have I heard that anti-vaccine people are dangerous even to the vaccinated population. Is that true? If so, how can it be? People say that germs will attack them, and soon they would ...
91
votes
6answers
20k views

Do beneficial viruses exist? If so, what examples are there?

Typically, people call viruses some kind of organic compounds that cannot reproduce autonomously and which lower the fitness of their hosts. Even the word "virus" means "venom" in Latin. But from the ...
87
votes
4answers
15k views

Does the string “…CATCAT…” appear in the DNA of Felis catus?

In Hofstadter's Gödel, Escher, Bach: An Eternal Golden Braid (GEB), the following claim appears: ...in the species Felis catus, deep probing has revealed that it is indeed possible to read the ...
86
votes
3answers
6k views

Why did the process of sleep evolve in many animals? What is its evolutionary advantage?

The process of sleep seems to be very disadvantageous to an organism as it is extremely vulnerable to predation for several hours at a time. Why is sleep necessary in so many animals? What advantage ...
83
votes
6answers
27k views

Are humans the only species who drink milk as adults?

I was drinking a glass of milk the other day and that got me thinking that no other animal to my knowledge drinks milk past their infant stages. One could argue that cats might but it isn't good for ...
81
votes
3answers
14k views

Is there an RGB equivalent for smells?

Millions of colors in the visible spectrum can be generated by mixing red, green and blue - the RGB color system. Is there a basic set of smells that, when mixed, can yield all, or nearly all ...
80
votes
5answers
24k views

How could humans have interbred with Neanderthals if we're a different species?

To be clear, I'm not doubting that homo sapiens and homo neanderthalensis did interbreed: of that much I'm convinced. Within the past few years I've seen an upcropping of pop-sci articles discussing ...
79
votes
4answers
96k views

Death because of distilled water consumption

One of my friends said that I would die if I drank distilled water (we were using it in a chemistry experiment) I gave it a go and surprisingly did not die. I did a bit of Googling and found this ...
79
votes
3answers
18k views

Why 20 amino acids instead of 64?

This question got me thinking about amino acids and the ambiguity in the genetic code. With 4 nucleotides in RNA and 3 per codon, there are 64 codons. However, these 64 codons only code for 20 amino ...
77
votes
2answers
19k views

Why is the heart not in the middle of the body?

All mammals that I can think of have a high degree of bilateral symmetry (In fact, almost every animal I can think of is like this). So why is the human heart not exactly in the middle of the body? ...
73
votes
3answers
15k views

How does the brain's energy consumption depend on mental activity?

What is the impact of mental activity on the energy consumption of the human brain? I am most interested in intellectually demanding tasks (e.g., chess matches, solving a puzzle, taking a difficult ...
70
votes
3answers
14k views

Why shouldn't dogs eat chocolate?

I was wondering why dogs shouldn't eat chocolate. Can't dogs just excrete the indigestible component in their droppings? It's common knowledge that dogs shouldn't eat chocolate. What I don't know is ...
69
votes
4answers
7k views

Why are there no wheeled animals?

In physics, "almost everything is already discovered, and all that remains is to fill a few unimportant holes." (See Jolly.) Therefore, on Physics SE, people are veering off into different directions: ...
69
votes
1answer
44k views

Why do Humans not produce Vitamin C like other mammals?

Why do most mammals produce their own Vitamin C? Why do Humans not?
68
votes
8answers
13k views

Why do some bad traits evolve, and good ones don't?

If a trait would be advantageous to an organism then why hasn't it evolved yet? Conversely, if a trait is not advantageous or mildly disadvantageous, why does it exist? In other words why does ...
67
votes
2answers
5k views

Do animals exhibit handedness (paw-ness?) preference?

I have been observing my cat and found that when confronted with an unknown item, she will always use her front left paw to touch it. This has me wondering if animals exhibit handedness like humans ...
65
votes
2answers
18k views

What is the evolutionary advantage of red-green color blindness?

Red-green colorblindness seems to make it harder for a hunter-gatherer to see whether a fruit is ripe and thus worth picking. Is there a reason why selection hasn't completely removed red-green ...
63
votes
2answers
3k views

Is there any evidence that sexual selection may lead to extinction of species?

Darwin suggested that sexual selection, especially by female choice, may counter natural selection. Theoretical models, such as a Fisherian runaway process, suggest that evolution of preference and ...
62
votes
4answers
8k views

Are there organisms with fewer than 1000 neurons?

I'm developing neural networks comprised of just 3 to 10 layers of virtual neurons and I'm curious to know if there are any insect brains out there with fewer than a thousand neurons? Are there any ...
62
votes
2answers
9k views

Do ants or other insects sleep, and if so why?

I was thinking yesterday about insects (as there was a spider in the house, and I couldn't help but think of anything else, even though they aren't insects), and I started to wonder if ants sleep? ...
62
votes
2answers
10k views

Can a woman give birth to twins with different fathers?

Is it possible for a woman to conceive from two different men and give birth to half-siblings?
61
votes
2answers
7k views

Why does it hurt the next day after doing significant exercise?

I think this is a fairly common observation that if one does some significant amount of exercise, he/she may feel alright for the rest of the day, but it generally hurts bad the next day. Why is this ...
61
votes
1answer
5k views

What could cause a forest of bent trees?

While hiking on the northern Idaho-Montana border, I encountered a large area where virtually every tree is bent at the base in the downhill direction. Only the very largest and very smallest trees ...
59
votes
8answers
10k views

Why does evolution not make our life longer?

Why does evolution not make life longer for humans or any other species? Wouldn't evolution favour a long life?
59
votes
4answers
7k views

Why do smaller mammals move intermittently?

I was watching a nice little video on youtube but couldn't help but notice how snappy smaller animals such as rats and chipmunks move. By snappy I mean how the animal moves in almost discrete states ...
58
votes
1answer
6k views

A new species of small bird?

This picture is take from my village in Gujarat, India. I think it is a small bird which I have never seen before. It is smaller than an Indian hummingbird and even smaller than a neem tree leaf. You ...
57
votes
4answers
12k views

How come large herbivores have such thin legs?

Edit: This question is very similar to this and related to this one (though the latter focuses on homology instead of scaling laws). However, the answer to this question is far more comprehensive, in ...
56
votes
5answers
33k views

Why don't mammals have more than 4 limbs?

Arthropods have 6 or more limbs and arthropods with 6 limbs appear to move faster than arthropods with 8 limbs so I wonder whether this might have something to do with fast and efficient locomotion. ...
55
votes
5answers
10k views

Life without DNA?

I'm by no means an expert in the field, merely a curious visitor, but I've been thinking about this and Google isn't of much help. Do we know of any lifeforms that don't have the conventional double-...
54
votes
4answers
34k views

Why do the fastest runners tend to be black?

If you watched the last Olympics like me you probably also observed that most medallists in running events were black. Why is that? I discussed this with university grad friends and researchers and we ...
52
votes
4answers
6k views

Why do men have nipples?

I'd be tempted to call nipples in men vestigial, but that suggests they have no modern function. They do have a function, of course, but only in women. So why do men (and all male mammals) have them?
52
votes
2answers
9k views

What is the benefit of fever during infections?

When people get sick, they often develop a fever. What is the effect of an increased body temperature on viruses and bacteria in the body? Is it beneficial to the infected body? Importantly, often ...
50
votes
11answers
22k views

Can humans survive without consuming life? [closed]

Some people say that it's awful that humans eat animals. They feel that it's barbaric, because you're killing life and then on top of that, you're eating it, and that you should eat vegetation ...
50
votes
4answers
8k views

What is the longest-lasting protein in a human body?

Protein life times are, on average, not particularly long, on a human life timescale. I was wondering, how old is the oldest protein in a human body? Just to clarify, I mean in terms of seconds/...
50
votes
3answers
4k views

Why does cracking a joint make noise?

What causes the noise when you crack a joint? Is joint cracking harmful?
49
votes
2answers
8k views

Why does cutting onion cause tears?​

When I looked on a couple of sites, I found that it is because of sulfuric acid produced by onions. But I could not find more details. What is the biochemical pathway by which onion causes tears? Also,...
49
votes
5answers
2k views

Human perception of time depending on age

From what I can tell and what thus far all people with whom I discussed this subject confirmed is that time appears to "accelerate" as we age. Digging a little, most explanations I found basically ...
49
votes
1answer
56k views

Why Does Salt Water Help Sore Throats?

I am having some trouble understanding how salt water, a simple solution, could so effectively remove the pains of a sore throat. I do believe that the answer is closely related to hypo/hyper-tonic ...
48
votes
9answers
10k views

Why are there no organisms with metal body parts, like weapons, bones, and armour? (Or are there?)

Reading this question, Why are there no wheeled animals?, I wondered why no organisms seem to make use of the tensile and other strengths of metal, as we do in metal tools and constructions. I am ...
47
votes
3answers
2k views

Can scientists create totally synthetic life?

This particular question has been of a great deal of interest to me, especially since it dives at the heart of abiogenesis.

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