Wikipedia:Reference desk/Archives/Science/2014 February 11

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February 11

Megalodon shark

What is the likely hood of a shark evolving into a previous form, if the conditions of today's planet were similar to previous atmospheric state would a evolutionary step reappear? IE a great white evolving into a form of megladon. A backwards evolution if you like. watched a documentary on the tv about a giant shark and thought rather than it being an extinct dinosaur it could be a new species as whale populations grow or a backward step due to conditions. Chromagnum. — Preceding unsigned comment added by Chromagnum (talk • contribs) 14:19, 11 February 2014 (UTC)

I do not think anyone can predict the likelihood. I just thought I would mention that if the relevant original genes from the original species were still present in the present day DNA, then there are such examples. I recall a frog i South America that evolved into a infant looking baby frog species, simply because there was a not enough of some kind of nutrition in its surroundings to let it grow to a healthy grown up frog. But such cases seem to be exceptions. Evolution , generally speaking does not go backward, see Devolution_(biology). DanielDemaret (talk) 15:13, 11 February 2014 (UTC)

Thanks. Chromagnum. — Preceding unsigned comment added by 41.254.1.240 (talk) 15:37, 11 February 2014 (UTC)

There are a few examples of evolution seemingly reversing direction. An absolutely classic example is the Peppered moth - which turned from a predominantly white moth into a predominantly black one during the industrial revolution in the UK when soot darkened the trunks of the trees that they settled on and light colored pepper moths became easier for predatory birds to find. When the Clean Air Act 1956 suddenly reduced the amount of sooty pollutants, the moths turned white again.

However, that is a slightly debatable matter - it's likely that there were a few black moths within the initial pre-industrial population - and it's known that a few white ones survived the industrial revolution. So this may simply reflect a shift in the relative numbers of two sub-species rather than an actual genetic change that became permanent and was subsequently 'reversed'. We don't have an occasional, very rare, Megaladon-like shark in modern populations - so there is no way for some small numbers of them to 'rebound' in the way that the light-colored pepper moths did.

According to the Florida Museum of Natural History, "Megalodon became extinct 2 mya. It is believed that during the rapid climate change of the Ice Age, there was a dramatic reduction in the number of large whales that Megalodon fed upon. This, along with competition from other predators (sharks) eventually led to the demise of the Megalodon." - so at the very least it would take an increased whale population and a new ice-age to favor that kind of large predator. Since whale populations are depressed due to human predation - and we're heading into global warming rather than a new ice-age, it seems dramatically LESS likely that giant sharks might again appear than it ever was in the past.

Whether that reverse-evolution is even possible depends on many things - do the genes for hugeness still exist in shark DNA? If they do - and are merely being suppressed by some other, more modern, gene - then it's possible for genetic defects in the modern gene to result in an occasional giant shark - and that could result in a reversal of evolution. However, if Megalodon just went extinct - without evolving into a more compact body plan...or if the way they survived was by losing the gene that made them huge - then the Megalodon is gone forever. Of course it's possible that some environmental pressure could force sharks to get larger - but they'd be unlikely to be Megalodons because evolution doesn't generally take the same exact path on more than one occasion.

Bottom line is "probably no".

SteveBaker (talk) 15:46, 11 February 2014 (UTC)

Also note that if any shark species regularly preyed on people, they would be quickly wiped out by us. Existing species of sharks rarely attack people, despite movies like Jaws. But, if it became unacceptably dangerous to swim in the ocean, then people would exterminate them, maybe keeping a few in aquariums. StuRat (talk) 18:40, 11 February 2014 (UTC)

Evolution of a similar form under similar conditions isn't unlikely at all. See convergent evolution. μηδείς (talk) 21:26, 11 February 2014 (UTC)

Ice on car windows

Why is making it cold inside the car more effective than making it warm in the car in melting ice. 82.132.214.146 (talk) 21:15, 11 February 2014 (UTC)

Give up! What's the answer?--Aspro (talk) 21:23, 11 February 2014 (UTC)

It isn't. If you have a source that says otherwise, please provide a link. μηδείς (talk) 21:25, 11 February 2014 (UTC)

I wonder if this is the result of chinese whispers of the advice to use cold water instead of hot water to defrost windscreens. I too call bunk, I don't believe making it cold is more effective then making it warm. Raising the temperature increases the rate at which ice melts. Vespine (talk) 21:45, 11 February 2014 (UTC)

Makes some sense though; the specific heat of water is high enough that even cold water will readily melt ice, and it's less likely to cause cracking due to a quick expansion of the glass in just one spot. various irreliable sources. μηδείς (talk) 21:56, 11 February 2014 (UTC)

This might just be a misunderstanding. The fastest defrost comes from directing all the heat to the windshield, and shutting off the heat to other parts of the interior. So making it cold doesn't help, but keeping it cold does, in a sense. Looie496 (talk) 21:51, 11 February 2014 (UTC)

Note: many cars turn on the A/C when defrosting the windshield. I noticed that for the Jetta, the A/C light goes on (most other cars, the A/C gets turned on without notification). The manual has an asterisk which explains: "*The AC is used to dehumidify the air." [1] -So, apparently, this is not to make the air colder. ~E:71.20.250.51 (talk) 22:26, 11 February 2014 (UTC)

Dehumidifying helps to stop moisture condensing, and sometimes freezing on the inside of the cold windscreen (even in the UK this can be an additional hazard), but warm air and warm water will melt the ice on the outside more quickly. Just don't use boiling water on a very cold windscreen because of the risk of cracking, but start with tepid water. I find that it can take several applications on a very cold morning to get rid of a thick layer of ice and to warm the windscreen sufficiently to avoid subsequent re-freezing before the car heater becomes effective. My favourite method is to put a (mains-powered) electric fan heater inside the vehicle half an hour before setting off. Not only does it clear all the ice and snow from all the windows, but it warms the inside of the car too, providing a much safer and more comfortable start to the journey. Dbfirs 22:38, 11 February 2014 (UTC)

Related article:  "Volkswagen testing ice and fog-free windshield coating" ~:71.20.250.51 (talk) 23:51, 11 February 2014 (UTC)

Note that the defrost setting also usually disables recirculate mode, to prevent moisture buildup from people's breath, etc. That is, it pulls in cold outside air, heats it, then blows it on the windows. When the car is first started, the heating part is rather minimal, until the engine warms up. So, it can literally be blowing cold air on the windows, at first.

I find I need to alternate between defrost mode, to clear the windows, and recirculate mode, to warm the interior of the car. Recirculate mode also stops exhaust from other cars being pulled in, so makes most sense when stopped at intersections or traffic jams, where exposure to bad air is more likely. I wish my car could detect bad air and switch to recirc mode automatically, then back to defrost mode when the air clears. (Of course, I'd want the ability to override it.) StuRat (talk) 14:41, 12 February 2014 (UTC)

That's why turning the A/C on with recirculate works best. The A/C gets the moisture out of the incoming air - and if you use recirc, it'll remove moisture from the air that's already inside the car too. Using recirc also prevents most of the new (possibly moist) air from entering the vehicle. Most people assume that turning on the A/C will also cool the air unpleasantly - but it's easily overpowered by the heat from the engine if you turn the temperature up. Of course if you don't have A/C - then this advice is of limited help! SteveBaker (talk) 16:09, 12 February 2014 (UTC)

I don't think the A/C removes moisture from the air as effectively as blowing it right out of the car and replacing it with dry outside air. In winter in my climate the outside air is very dry, while the inside air gets moist quickly from my breathing, etc. Also, A/C can put quite a load on a small engine, so you want to avoid using it when not needed. StuRat (talk) 18:13, 12 February 2014 (UTC)

Link on "Leuprorelin" page goes to wrong info

Hi,

Wanted to know if someone could please fix a wrong link on your "Leuprorelin / leuprolide" page. In "Links" section, the "National Women's Health Network's (NWHN)" article on Lupron is referenced and linked. But the link only brings one to Wikipedia's NWHN page, and does *not* provide the NWHN article on Lupron/leuprolide.

The correct link to the NWHN's Lupron article is as follows: http://nwhn.org/lupron%C2%AE-%E2%80%93-what-does-it-do-women%E2%80%99s-health . Can someone make this correction?

Thank you.

108.20.242.221 (talk) 21:48, 11 February 2014 (UTC) ==

This is not the right page to make such requests. Here we provide links and references to answer user questions. You should leave your message on the article's talk page (linked at the top of that article), so that people familiar with the subject will be notified. μηδείς (talk) 22:03, 11 February 2014 (UTC)

need help on homework because I am stuck on it

Why is Newton's first law sometimes called the law of inertia? — Preceding unsigned comment added by 173.81.163.73 (talk) 22:09, 11 February 2014 (UTC)

We don't do your homework for you, but you might like to read the articles on Newton's laws of motion#Newton's first law and Inertia and ask if there is anything that you don't understand. Dbfirs 22:30, 11 February 2014 (UTC)

Can you help me answer this? Use what you know about inertia to explain why you feel pressed back into the seat of a car when it accelerates. — Preceding unsigned comment added by 173.81.163.73 (talk) 22:14, 11 February 2014 (UTC)

The term "inert" means "inactive". The link mentioned above should answer your questions, but if it still doesn't make sense, come back and tell us what the stumbling block is. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:44, 11 February 2014 (UTC)

you need to understand the concept of inertia,acceleration and force. Then you need to read the Newton First Law. It's pretty basic. 202.177.218.59 (talk) 22:46, 11 February 2014 (UTC)

... and Newton's laws of motion#Newton's second law for your second question. Dbfirs 00:19, 12 February 2014 (UTC)

Modes of transmission of non infectious diseases

Header added: 23:25, 11 February 2014 (UTC)

modes of transmission of non infectious diseases its causes , causative agents and treatment.2.49.2.24 (talk) 22:58, 11 February 2014 (UTC)

See: Vector (epidemiology) — If you still have any specific questions, feel free to ask. ~:71.20.250.51 (talk) 23:25, 11 February 2014 (UTC)

But a non-infectious disease, by definition, is one not spread by vectors. I suppose genetic diseases can be said to be transmitted to offspring, even though not infectious. Gene therapy is one way to treat those.

Many diseases are also caused by environmental factors, which can be passed onto others. For example; smoking, eating unhealthy foods, living in polluted areas, etc. See memetics. Behavior modification therapy is one way to treat those.

Poverty can also be considered a cause of disease, and is passed down. Reducing poverty requires a sustained effort to educate, train, and employ people at a living wage. Providing free healthy foods, homes/utilities, child care, and medical/dental/vision care would also help. To deal with the lack of incentive to work, those things not needed for optimal health, like TV, video games, computers, fancy clothes/shoes, eating at restaurants, vacations, cars, jewelry, etc., should only be available by working for them (so don't just give people on welfare cash, as they might spend it on these things). StuRat (talk) 14:50, 12 February 2014 (UTC)