Human beings have evolved from their ancestors to their modern forms adapting many changes in structure and I would assume that every change has a significance.  So, what is the cause of our hair turning white at old age? Was it meant for frightening away predators at old age when our body is weak? Or what is it actually?
122672
A vast majority of humans get at least some grey hair as they age. As far as I know this applies to both genders and all races. Presumably this means that at least some grey haired humans have noticeable reproductive advantage, or maybe they had it in the recent past.  Theoretically, because this feature is so prevalent, there must be a strong evolutionary pressure to keep it. Am I right? If so, what is it?
91323
Many older movies seem to have vivid reds and particularly realistic or noticeable skin tones (they certainly seem to stand out from typical skin tones on TV or the majority of movies). This applies even in DVD or online versions and is not, given the range of material I've noticed the effect in, an artifact of special post processing or deliberate colour manipulation.  All the movies I've noticed the effect in are from the film era, especially from when colour became common to the late 1960's. I used to think it was just Technicolor but I've seen things recently that don't claim to be Technicolor that also show the effect.   claims the effect was due to the final print being constructed late in the process for separate black and white film strips for each primary colour allowing the final dyes to be very vivid and clear:     The rich colors that the Technicolor process gave came in part from the fact that the color was not added to the process until the final stages. The color information was recorded and processed as separate black and white images which were relatively easy to control and preserve.   Is this a good explanation?
13795
Some hair especially body hair regrows after trimming but stops growing after a while. What is the mechanism behind control of hair growth and how is the length limit determined?
14279
Why does evolution not make life longer for humans or any other species?  Wouldn't evolution favour a long life?
89123
The question "why do we age" has been asked numerous times. But why are we young? The cells of the adult human being are an age (time>0), but how can old cells create new cells that are younger than themselves?  I.e, how are young people made from the cells of old people?  I realize that senescence, the act of a cell aging, has to do with the shortening of telomerase over time which puts a limit (the Hayflick limit) on the life of an autosomal cell. So in theory, because cells only make direct copies of themselves but the telomerase shortens with every division, each new daughter pair would be as old as the parent and would continue aging. But how come new people start senescence at time t=0?
123602
I am not even remotely an expert in this field; I just got curious, so help me.   First of all, let us remove all human sentimental attributes from this question (such as connotations of  or emotional reactions thereof) and ask it from a purely scientific point of view. The typical facial feature of a West/Central African person (the so-called ) exhibits a wide nose, a lack of nasal bridge projection (similar to many Asian noses) and a prognathous skull shape that resembles more closely to our ancestor Homo Heidelbergensis than many other indigenous phenotypes from other parts of the world do.  I agree that this claim sounds anecdotal, and is certainly not true of all Africans (for example, Ethiopians), but one cannot dismiss it simply on grounds of ethical policing. I cannot help but notice that many of my African friends remind me of our shared ancestry (with no disrespect meant whatsoever), as is clear from the photographs below, one of a supposed Homo Heidelbergensis and one of a random African Homo Sapiens of today.     My question is the following. What is the reason behind this seeming resemblance? Is this appearance an illusion and possibly a construct of a prejudiced mind, or does this have a valid scientific answer? For example, are most Africans closer to our ancestors than the rest of humanity is? How does evolution answer this question?  Thank you for your help.
108544
My question here is about evidence for evolution from Embryology and from Genetics.  Mammals do have similar Embryos, but is it the case that for each species there is an embryonic development that occurs in earlier species, has such relationship been observed? What I mean for example if we generally conceive of having species$Sp_1,Sp_2,...,Sp_n$ where each $ Sp_{i+1}$ being evolved from $Sp_i,$ then is it the case that the embryonic development stages of $ Sp_{i+1}$ contains some of the embryonic development stages of all of its ancestor species.  Similar question to 1 but regarding Genetics, is it the case that every species has a genetic thumbprint of its ancestors that lie there in the non-functional sections of its DNA, i.e. is it the case that all the genetic history of our evolution is recorded in the non-functional section of our DNA. So do human DNA have some portions of the DNA of some dinosaurs for example?
45851
When I watch wilderness specials for more than a few minutes, I notice a familiar pattern: predators are depicted as being alerted by the scent of blood. Wounded animals seem to make the best prey and predators seem to have a heightened awareness for the smell of blood.   It would seem that it would then be a disadvantage to evolutionary survival for female organisms to menstruate. How do females of a species not attract predators to the signal of menstrual blood?   Do female organisms in the wild actually menstruate? If so, is there a difference in the composition of menses that does not alert predators? How would this not at the very least give predators an idea of the general vicinity of the female?  If wild animals excrete their menses, do they have ways in which they are able to mask the evidence of its release or are they somehow internalizing the tissue so that they are not released?  If female organisms in the wild do menstruate, then why is this not a survival disadvantage?
118823
I'm Soumya, an author from India.  A reader has challenged me about the use of the word 'hairs' in my book. I have used, 'a few hairs' and that's justified, as hair is a countable noun in that very phrase. But I'm at a confusion for some other sentences. Could you kindly tell me if I'm wrong grammatically?   "The evening zephyr ruffled their long flowing hairs - the Indian village girl's shiny, black hair, and Audrey's curly blonde hair." "They had golden or brown or ashen hairs." "His black and white hairs had now turned into complete white."   Could you please help? Thank you!
47327
I remember reading a story once where we had all interbred such that there were no longer any blacks, whites, Asians, etc.  We were all 'brown'.  Somehow they 'found' 5 children that were purebred 'races', and I don't remember much else.
87614
As the title says, when and what made Voldemort look the way he does (pale, snake-like etc) as opposed to how we've seen him in his earlier years as Tom Riddle? Is it just a side effect of his unnatural resurrection? Before he died attacking Harry as a baby did he look like a normal guy?
37423
Just wondering ; I get the impression a large number of multicellular organisms are multi-lateral in their physical structure. Why would evolution/mutation have retained multi-lateral symmetry in an organism? What advantage/s does symmetry provide an organism?  EDIT:  By multi-lateral symmetry I mean at-least bi-lateral symmetry (as in the case of many beings such as elephants, crabs and fishes), but perhaps more than bi-lateral too (starfish come to mind)  END EDIT:
70019
I've been looking around and cannot find a definite answer on what it is that tells trees to change their metabolism and drop leaves. I see that such activity is called .  What interests me are the specific mechanisms by which a tree knows that it's time to drop leaves. Is it photoperiod shortening (day duration?) Is it temperature changing metabolism? Is it build up of some toxic compound?  Thank you for your input!
73494
Given that the mechanism of natural selection is sensitive, how do species survive in an evolutionary midway? The ability to breath in air requires complex protein systems. An animal that is developing these organs would not be able to utilize its function until it fully evolves. While it doesn't, wouldn't the wasted resources used in growing half-developed lungs be.. wasted? Or is all evolution continuous?
51432
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 did it give the individuals that evolved to have it as an adaptation? When and how did it likely occur in the evolutionary path of animals?
55402
There seem to be a number of ideas about why we age. Hypotheses include the gradual accumulation of cell metabolic products affecting organism function and the reduction of  during cell division. My hand-wavey idea would be "wear and tear".  Are we anywhere near a consensus theory of senescence?
112166
The answer can be "Because it doesn't!" or "It wasn't needed!" in short but there might be a historical or linguistic explanation behind this. (Of course, every language might be lacking a word that another language has and you can give the meaning in a context.)  This question came up mainly because there are several languages which has separate words for head hair and body hair. For example, head hair is capelli in Italian, saç in Turkish, cheveu in French and kopfhaar in German. But in English, hair is like a hypernym for head hair and body hair.  When we check the , the origin is related to the German word haar. And interestingly, German language came up with kopfhaar which literally means headhair.     Old English hær "hair, a hair," from Proto-Germanic *khæran (cognates: Old Saxon, Old Norse, Old High German har, Old Frisian her, Dutch and German haar "hair"), perhaps from PIE *ghers- "to stand out, to bristle, rise to a point" (cognates: Lithuanian serys "bristle;" see horror).    When we dive into , we can see that there are structural differences between body hair and head hair but they are composed of the same substance, keratin. Though, there is a distinction in terminology:     Androgenic hair, colloquially body hair, is the terminal hair that develops on the human body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color.   And a twist ending: Wiktionary has a definition (and even an etymology) for "":     From Middle English *heed-heer, from Old English hēafodhǣr (“hair of the head, headhair”), equivalent to head +‎ hair. Cognate with Dutch hoofdhaar (“headhair”), German Haupthaar (“headhair”), Danish hovedhår (“headhair”), Swedish huvudhår (“headhair”).   I can see that "" is used in a few sources but it is not common. Personally I haven't encountered this word before I did this research.    How come both "hair" and "headhair" emerged (for the same meaning)? Why didn't "headhair" gain a common usage? What happened in the history? Does "headhair" have a current usage? (only in technical sources?)     Note: Just to emphasize, the question is not only about finding words, its about the history and origin of the words as well. Also, the question can be: "Why doesn't English have a common separate word for “head hair”? (head hair vs. body hair)"