99 votes

Can a person survive on blood in place of water?

Blood is not a good source of water. 1 liter of blood contains about 800 mL of water, 170 grams of protein and 2 grams of sodium (calculated from the composition of lamb blood). When metabolized, 170 ...
Jan's user avatar
  • 8,059
75 votes
Accepted

Are humans the only species who drink milk as adults?

Good observation! Gene coding for the lactase Gene LCT Mammals have a gene (called LCT C/T-13910) coding for the lactase enzyme, a protein able to digest lactose. ...
Remi.b's user avatar
  • 68.1k
70 votes

Can the dead be brought back to life by viruses?

You must tell facts from fiction; viruses need living cells to replicate because they do not have the molecular machinery at hand to generate energy and construct building blocks essential to life. So ...
AliceD's user avatar
  • 52.4k
53 votes

What makes a cancer contagious?

There are two relatively common contagious cancers: Tasmanian Devil Facial Tumor, and Canine Transmissible Venereal Tumor. Both are truly contagious cancers, in that the cancer cells themselves are ...
iayork's user avatar
  • 14.2k
49 votes

Do we know all the possible human hair colors?

Melanin is the only biologically coded for pigment amongst mammals and most animals broadly speaking. Some birds are exceptional in this case where reds and greens can be seen (in which case often ...
小奥利奥's user avatar
43 votes
Accepted

Why do human females have periods?

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 ...
AliceD's user avatar
  • 52.4k
43 votes
Accepted

Why do diseases in the tap water of developing countries affect people from developed countries more?

You can expect that someone drinking from a water source regularly will develop immunity to the pathogens in that water source by being repeatedly exposed to them. However, it's not quite right to say ...
Bryan Krause's user avatar
  • 45.3k
42 votes
Accepted

Why do the fastest runners tend to be black?

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?" ...
Forest's user avatar
  • 1,879
42 votes
Accepted

How can the organic mercury compound Thiomersal be not dangerously toxic?

Thiomersal is broken down into two compounds, thiosalicylate and ethylmercury (Ensink 2015). The thiosalicylate it is relatively non-toxic, and there is even some evidence that this compound could ...
rotaredom's user avatar
  • 2,711
41 votes
Accepted

Why is it advised that infants are fed mother's milk?

The phrase "Breast is best" is a hotly debated one (source: The Guardian and personal communications with many folks). The reason why we don't want to feed infants cow's milk is, however, anything but ...
AliceD's user avatar
  • 52.4k
40 votes

Is it possible that by mutation a human could see infrared or other 'colours'?

Yes. Far-red vision (>700nm) The ability for retinal-binding proteins to absorb far-red (between 700nm-850nm) light has been experimentally confirmed in this paper. While the authors did not attempt ...
March Ho's user avatar
  • 9,442
40 votes

Can humans ever directly see a few photons at a time? Can a human see a single photon?

A single molecule of rhodopsin (actually the cis-retinal bound to it) can and actually does react to one photon (Purves et al. Chapter: Phototransduction in Neuroscience). It has been estimated ...
WYSIWYG's user avatar
  • 35.5k
39 votes
Accepted

Why did scientists state that the Omicron COVID-19 variant was a reason to get a booster?

(note: I'm simplifying things a bit here by only talking about antibodies; I don't mean to downplay other aspects of the immune response, just to keep it focused for a lay audience) Natural antibody ...
Bryan Krause's user avatar
  • 45.3k
38 votes
Accepted

Are there biological reasons why life expectancy is lower for men in most countries of the world?

There are both biological and social factor for that: Biological Females have two X chromosomes. When mutations in genes of the X chromosome occur, females have a second X to compensate. Males, on ...
Thai's user avatar
  • 647
36 votes
Accepted

Can Biologists identify all viruses?

Do physicians/biologists not know all the different types of viruses out there? No, Biologists don't know all the viruses that exist out there. There's a lot! We do know many of the ones infecting ...
YviDe's user avatar
  • 2,258
36 votes

Are red blood cells prokaryotic?

When differences between prokaryotes and eukaryotes are taught in an introductory biology course, a generic prokaryotic cell and a generic eukaryotic cell are typically compared. Cells in a complex ...
De Novo's user avatar
  • 8,801
36 votes
Accepted

Can a cancerous cell from outside cause cancer in a healthy person?

Can a cancer cells from someone else's body cause cancer in a healthy person? No. Cancer cells from another person cannot cause cancer in a healthy person. The rare cases of transmissible tumors all ...
De Novo's user avatar
  • 8,801
36 votes
Accepted

What is the human energy consumption by organ?

Percent of basal metabolic rate by organ (BC Campus Open Education): Liver and spleen : 27% Brain: 19% Skeletal muscle: 18% Kidneys: 10% Heart: 7% Other tissues (lungs, intestine, skin, bone, fat ...
Jan's user avatar
  • 8,059
35 votes

Are humans the only species who drink milk as adults?

The problem with this question is 1) wording and 2) access. "Drink" and "digest thoroughly" are two different things. The latter does not prohibit the former. It is only lactose that is not tolerated;...
anongoodnurse's user avatar
33 votes
Accepted

Do men and women have the same number of genes?

It is true that the Y chromosome is shorter than the X chromosome and that there are more genes on the X chromosome. Do men have fewer genes? One could (mis)understand three things in the ...
Remi.b's user avatar
  • 68.1k
32 votes
Accepted

How is heavy water detrimental to the human body?

The question is already answered by Armand. I am just going to elaborate on that by referencing the paper. Different isotopes of chemical elements have slightly different chemical behaviors, but for ...
Nilay Ghosh's user avatar
  • 1,213
28 votes

Can a cancerous cell from outside cause cancer in a healthy person?

Before OP edited his/her question, it was a little unclear whether the question was only about humans. The following answer is more general than asked as it also considers cancers in non-humans Most ...
Remi.b's user avatar
  • 68.1k
28 votes

Can humans ever directly see a few photons at a time? Can a human see a single photon?

A recent study published in Nature by Tinsley et al. Direct detection of a single photon by humans found that it is possible for dark-adapted humans to respond to a single-photon stimulus, but only ...
llama's user avatar
  • 439
27 votes
Accepted

Cells of umbilical cord - mom's or son's?

Cells of umbilical cord - mom's or son's? Answer: Son's. The interface you are looking for is in the placenta. https://en.wikipedia.org/wiki/Placenta Formally the fetal side of the placenta is ...
JayCkat's user avatar
  • 2,916
26 votes

Is sex a spectrum?

Short answer: it's messy, and probably no answer will satisfy everyone. I'm only going to consider sex (I'm not going to mess with "gender") in humans. It's reasonable to consider sex as ...
Ben Bolker's user avatar
  • 5,344
24 votes

Can Biologists identify all viruses?

It's a cost/benefit situation. Yes they could have taken samples, processed them, teased out the virus, and eventually identified exactly what virus (sort of*) that your girlfriend had by its gene ...
Nathan's user avatar
  • 1,152
24 votes

Are humans the only species who drink milk as adults?

Just to point out an exception, adult cows sucking other cows' milk are not uncommon. At least, it's common enough to be a concern in dairy farms and for simple fixes to have been developed. The usual ...
Pere's user avatar
  • 586
24 votes
Accepted

Can UV radiation be safe for the skin?

You're talking about long-wave UV, or UV-A radiation. In the 80s, experts claimed that this was a safe wavelength. Protection against UV-A was not part of sunscreen in the early days. Consequently, UV-...
S Pr's user avatar
  • 6,202
23 votes
Accepted

Is monogamy a human innate behaviour?

Humans are believed to be mostly serial monogamists with a noticeable components of secret cheating. Serial monogamy means most will have a single partner at a time but will likely have several ...
John's user avatar
  • 14.6k

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