Wikipedia:Reference desk/Archives/Science/2010 April 24

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 24

Energy used in travel

How many joules of energy are expended by each of the following 16 entities? (Additional details for each of the 16 entities: Please deal with entity variations by providing minimum and medium and maximum values; or please specify a typical specimen and provide a value for that specimen. Please assume that there is no wind in the air and no current in the water.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC)
[I am inserting the underlined text. -- Wavelength (talk) 03:34, 24 April 2010 (UTC)]

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.. --Jayron32 03:34, 24 April 2010 (UTC)

None of these questions is a homework question. I am simply curious about all of them. -- Wavelength (talk) 03:39, 24 April 2010 (UTC)

In that case, these are insansely complex problems anyways. The work done by each body in traveling one kilometer. Its a rather complicated problem, since in a perfect frictionless system, the work = 0 if the movement is at a constant velocity. So the work done in traveling one kilometer is the work done overcoming friction. These systems are fantasticly complex; you could calculate joules of energy consumed in traveling that distance for some of these. For example, given a car with a fuel efficiency of 30 km/gallon of gasoline you could calculate the mass of gasoline burned and then the joules of heat released in burning that gasoline from the Heat of combustion value for gasoline. For the human examples, there are ways of calculating "food energy" consumed per minute for various activities, but these are usually pretty inaccurate measurements. Still, you can find calculators online that will do this for you. Then you just need to convert from food calories to joules. --Jayron32 03:49, 24 April 2010 (UTC)

Remember that in both air and water, drag is really important as speed increases (drag increases with the square of the speed). So the speed needs to be known for all the mechanical systems. There are also questions of efficiency. Some engines are more efficient at high speed -- airplane engines are more efficient at the low temperatures of high altitude. The air is also much thinner there. At 1 km altitude, air friction would be quite high and the engines not as good. An aircraft blog I visited earlier gave an economy of ~2.7L/100km/passenger for a Boeing 777-300ER and ~3.1L/100km/passenger for an Airbus A330 and that's overall with most of the flight at ~10km altitude and Mach 0.82 or so (see comment 9 here). -- Flyguy649 ^talk 04:28, 24 April 2010 (UTC)

Also, another difficulty is that airplanes weigh anywhere from a couple hundred pounds to over a million pounds. The An-225 would use an absolutely incredible amount more energy than the CriCri, and the engines are optimized for completely different altitudes. The same (in terms of the weight) goes with automobiles (though not as extreme) and the other things you mention. Even amongst airliners, there will often be a significant difference between types. Falconus^{p t c} 05:02, 24 April 2010 (UTC)

My clarification about "entity variations" applies to all those variations. -- Wavelength (talk) 21:31, 24 April 2010 (UTC)

Extended content

Energy used in travel: by a man walking How many joules of energy are expended by a man walking along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man running How many joules of energy are expended by a man running along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man bicycling How many joules of energy are expended by a man bicycling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man swimming How many joules of energy are expended by a man swimming along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man pedaling a pedal boat How many joules of energy are expended by a man pedaling a pedal boat along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man rowing a rowboat How many joules of energy are expended by a man pedaling a rowboat along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a horse with a rider How many joules of energy are expended by a horse carrying a rider along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a horse with a carriage How many joules of energy are expended by a horse pulling a carriage along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a motorcycle How many joules of energy are expended by a motorcycle traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by an automobile How many joules of energy are expended by an automobile traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a bus (omnibus) How many joules of energy are expended by a bus traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a ferryboat How many joules of energy are expended by a ferryboat traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a steam locomotive How many joules of energy are expended by a steam locomotive traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a diesel locomotive How many joules of energy are expended by a diesel locomotive traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by an airplane (aeroplane) How many joules of energy are expended by an airplane flying along a distance of one kilometer in a straight line at an altitude one kilometer above sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a helicopter How many joules of energy are expended by a helicopter flying along a distance of one kilometer in a straight and horizontal line at an altitude one kilometer above sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC)

16 questions from Wavelength collapsed, all identical except for the vehicle. Comet Tuttle (talk) 06:30, 24 April 2010 (UTC)

Could they please be removed? They're screwing up the Table of Contents 82.43.89.71 (talk) 23:41, 24 April 2010 (UTC)

They were not a problem to the Table of Contents until they were collapsed in a recent revision. If they are removed, the discussion will be hanging without the complete context. If the collapsing is not going to be undone, the main heading can be reworded to say "Energy used in travel (collapsed subheadings non-functional in links)", that is to say, including the links in the Table of Contents. But However, I prefer that the collapsing be undone. -- Wavelength (talk) 05:45, 25 April 2010 (UTC)

[I am revising my post of 05:45, 25 April 2010 (UTC). -- Wavelength (talk) 15:31, 26 April 2010 (UTC)]

Are you sure this is what 82.43 is referring to? My guess is the complaint is about the very large TOC due to the 16 additional items (that's aboutmore then the average, and possibly median, of a whole days worth), not the inability to navigate to the individual sub-questions; and that problem occured both before and after the collapsing Nil Einne (talk) 06:35, 25 April 2010 (UTC)

See Bicycle_performance#Energy_efficiency for figures for three of the above. 89.243.216.99 (talk) 13:11, 25 April 2010 (UTC)

You'll be able to find some details for cars, planes etc in Part I of Without Hot Air by David MacKay. 131.111.30.21 (talk) 16:14, 26 April 2010 (UTC)

Thank you, 89.243.216.99 and 131.111.30.21, for your replies and those links. -- Wavelength (talk) 22:10, 26 April 2010 (UTC)

Why no plastic beer bottles?

Why do I never see beer in plastic bottles sold anywhere? Why are they either in aluminum or glass? --70.179.176.30 (talk) 04:09, 24 April 2010 (UTC)

Beer is often sold in plastic bottles at punk/skinhead/metal/etc. gigs. It hurts the singers and band members less when people hurl the bottles at their heads. Also makes it harder to use bottles as weapons when the crowd start beating on each other. :) --Kurt Shaped Box (talk) 04:20, 24 April 2010 (UTC)

(edit conflict) Well, not demonstratably true. For over a decade Anheuser-Busch has sold beer in plastic bottles, and they weren't the first, Miller started some time before they did. Plastic bottles are not as popular as beer sold in cans or glass, tradition being what it is, but they certainly exist. You see them a lot more at major events like ball games or rock concerts, where glass is a concern for safety reasons. However, you can find them in grocery stores and other places where you can buy beer. --Jayron32 04:22, 24 April 2010 (UTC)

I'm pretty sure that I've bought plastic 500ml bottles of Bud in England before, FWIW. --Kurt Shaped Box (talk) 04:29, 24 April 2010 (UTC)

Aye, well, most bottled water is sold in plastic. :) --KägeTorä - (影虎) (TALK) 18:18, 24 April 2010 (UTC)

http://www.packaging-gateway.com/features/feature79/ has some comparisons and consumer info. You can do your own research with Google on beer plastic bottles. PrimeHunter (talk) 04:38, 24 April 2010 (UTC)

Interesting link — it seems to claim the major reason is that more oxygen gets into the bottle while it's on the shelf; but I thought plastic was airtight, and don't particularly see why the cap on a plastic bottle would let in more oxygen than the cap on a glass bottle. Comet Tuttle (talk) 06:28, 24 April 2010 (UTC)

Interesting enough, it also mentions cost. I presume this is in comparison to aluminium cans rather then glass bottles but don't really know. This [1] mentions cost as a factor in 2001. As an aside, plastic bottles are common in stadiums as has been mentioned, but while not as dangerous as glass, they still pose a threat, particularly of course when full and sealed. Stadiums sometimes limit bottle size (even for brought in bottles) as a result. Similarly, tap beer with paper or plastic cups for the beer [2] Nil Einne (talk) 07:24, 24 April 2010 (UTC)

The plastic is not airtight! The plastic allows diffusion of gas, depending on the exact material this diffusion is varying. The oxygen diffuses into the beer and changes the taste by oxidation reactions. There are certain surface treatments necessary for beer bottle to lower this diffusion. There is a book about the properties of polymers which has a good introduction [3] --Stone (talk) 08:12, 24 April 2010 (UTC)

For me, drinking beer from a plastic bottle would be like drinking water from a muddy puddle. It's just not preferred, when inert glass is available. Vranak (talk) 14:25, 24 April 2010 (UTC)

Glass and aluminium cans are much more recyclable than plastic - going to plastic bottles would be a retrograde step. SteveBaker (talk) 18:04, 24 April 2010 (UTC)

To me the Q shouldn't be why beer isn't commonly sold in plastic bottles, but why soda-pop is. It goes flat much faster in plastic, because the plastic isn't airtight, and the bottle may also leach chemicals out of the plastic, into the contents. StuRat (talk) 18:18, 24 April 2010 (UTC)

Similar question: Why in the US is water not sold in 2 liter bottles? This came as a shock to me when I tried to buy it, and had to settle for two 1 liters. Staecker (talk) 22:43, 24 April 2010 (UTC)

Because it comes in gallons. Like milk. How it's decided what is sold in gallons and what is sold in liters is one of the great mysteries of life.

Of course ...while I can understand a single serving, it feels pretty crazy to buy an entire gallon of tap water that someone has put into a bottle. I get that stuff literally piped into my house! APL (talk) 03:15, 25 April 2010 (UTC)

I suspect that the answer is that US manufacturers tend to stick with traditional units (ounces, pints, quarts, and gallons; in this case), until they reduce the size and want to hide this fact from consumers. Then they switch to metric to maximize deception and confusion. This happened with car engines, where a muscle car engine went from 455/460 cubic inches to 5.7 L, so nobody would notice that it was now 3/4 as big. This prevented consumers from trying to pay 3/4 as much. I wonder if any company has then done the reverse, and switched back to traditional units, when they next need to deceive consumers about another decrease in size. StuRat (talk) 07:18, 25 April 2010 (UTC)

Well it's easy to buy 1 liter of water (or soda), even though this is slightly more than a quart. Staecker (talk) 11:59, 25 April 2010 (UTC)

But were the previous bottles a quart (32 ounces), or maybe 36 ounces, slightly larger than a liter ? StuRat (talk) 15:00, 25 April 2010 (UTC)

Catabolic breakdown of muscles

Hello. I've heard many a bodybuilder say that catabolism starts breaking down muscles after about six hours of fasting. However, it seems quite exaggerated to me, so I've come here to seek a scientific answer. For an average person, how much time without eating does it take for the body to start breaking down muscles noticeably to feed itself?

(By "noticeably", I mean to the point that the bodybuilder may lose the muscle mass he has gained by working out during the day, or more). Thank you guys! --95.120.13.224 (talk) 08:35, 24 April 2010 (UTC)

Since they aim to get their fat to muscle ratio to the minim I expect their energy reserves are low. This is an area that the military have long been interested in, maybe another wikipedian knows of a good s reference. You might find of interest some of the things gone into on this site [4]. Fasting adds a complication because metabolism tends to slow down under these conditions.--Aspro (talk) 09:39, 24 April 2010 (UTC)

We may simplify anabolic/catabolic relationships as follows (for an average adult): 1. For about 3-4 hours after a mixed meal, glucose and amino acids and free fatty acids are coming from the gut into the blood; insulin levels are high and glucose is actively moved into liver, kidneys, and muscle, where it is stored as glycogen in all three, and amino acids are moved into muscles and incorporated into protein. From about 4 to 16 hours after a meal, insulin levels fall gradually, and blood glucose levels are maintained by glycogenolysis from liver and kidneys (not muscle), and there is little net uptake or output of amino acids from the muscle. By 16 hours (with wide variation), liver and kidney glycogen is depleted (not entirely gone) and insulin levels are low enough to allow catabolism of both fat and muscle for purposes of making glucose by gluconeogenesis. This is also when ketogenesis from fat breakdown begins. See Cori cycle. This is somewhat oversimplified, as there is considerable overlap between end of glycogenolysis and start of gluconeogenesis, but perhaps is a useful way to think about it for clinical and physical culture purposes. alteripse (talk) 11:13, 24 April 2010 (UTC)

It seems to me that the time frame would change dramatically based on activity levels, with each step taking far longer when asleep than while running a marathon. So, what activity levels were assumed for those values, Alterprise ? Also, doesn't the nature of the last meal matter, with sugars being digested far quicker than fats ? StuRat (talk) 11:19, 24 April 2010 (UTC)

Overnight resting. The major fuel source for muscle activity is muscle glycogen, which is used in muscles during exercise, and not for ordinary between-meal blood glucose maintenance. This partial separation reduces the exercise effect on whole body metabolic balance but amplifies it for in-muscle glycogen balance. Speed of digestion has an early effect which is why I specified mixed meal, but has little effect on the timing of the later stages. We use cornstarch to prolong digestible glucose intake in people whose glycogenolysis and gluconeogenesis is defective but it only adds a couple hours at best. So does a huge high fat meal. alteripse (talk) 11:27, 24 April 2010 (UTC)

Number of cells in a human body

How many (approximately) cells are there in a (an average, adult) human? RJFJR (talk) 13:10, 24 April 2010 (UTC)

Close to 50 trillion cells. However, that conflicts with Human_flora#Gut_flora which declares it to be about 10 trillion cells and Cell (biology) at a 100 trillion. Is this assuming a standard human of 70 kg I wonder? Looks like we will have to do a little proof correcting on these articles. --Aspro (talk) 13:38, 24 April 2010 (UTC)

Do you mean total number of cells, or number of Human cells? I've read somewhere (sorry, no reference yet) that the number of non-human cells (for example, bacteria in the gut and on the skin) out-number the cells that actually have your own human DNA.24.150.18.30 (talk) 15:11, 24 April 2010 (UTC)

The OP's word "in" an average human must include gut flora. Cuddlyable3 (talk) 15:39, 24 April 2010 (UTC)

And do we include dead cells ? A good portion of the skin is dead, so that makes a diff. StuRat (talk) 15:20, 24 April 2010 (UTC)

This must be a harder thing to estimate than it at first appears, as I can't find any references to this in my human physiology text books nor on any of the human genome sites, etc. To give the OP a figure could we say: The average human adult is composed of cells numbering between the magnitude of 1 x 10^13 and 1 x 10 ^14. --Aspro (talk) 16:10, 24 April 2010 (UTC)

Well, Human_flora#Gut_flora and Cell (biology) are compatible, as there are indeed roughly 10 times more non-human than human cells in a human. So Cell (biology) apparently counts all the cells that are inside a person. --Stephan Schulz (talk) 20:06, 24 April 2010 (UTC)

What is strange here is that humans are colonies of cells. So, you have intelligent colonies of cells that have difficulties estimating how many cells they themselves consist of :) . Count Iblis (talk) 20:46, 24 April 2010 (UTC)

Katla

Hi. If Katla were to erupt, how much water vapor would be released into the atmosphere and how much sea level rise would occur from the melted glacier (I previously calculated a figure of 0.3 mm)? Considering both the vapor released into the troposphere and stratosphere, what would be its equivalent CO₂e warming effect as an increase in equivalent carbon dioxide concentrations in ppm? Finally, would the net result from the combination of the ash, sulfur, and vapor ejected from the volcano produce net warming or cooling of the Earth globally in terms of surface temperature, or is this indeterminate? Thanks. ~AH1^(TCU) 13:43, 24 April 2010 (UTC)

I believe volcanoes typically cool the Earth, since the additional sunlight and heat reflected back into space from the ash clouds outweigh all the other factors. StuRat (talk) 15:17, 24 April 2010 (UTC)

I agree. To get a significant warming effect, you need to have an enormous eruption in which huge quantities of CO2 are emitted. Then, because of the long atmospheric lifetime of CO2 (far longer than that of the dust and aerosols), you can get a warming effect. Note that H20 only has a short atmosheric lifetime. I think that even supervolcano eruptions are not large enough; they will still produce a net cooling effect. But large flood basalt eruptions, such as the one that formed the Siberian Traps, will lead to a net warming effect. Count Iblis (talk) 15:52, 24 April 2010 (UTC)

CO2 lives in the upper atmosphere for thousands of years. So I'd expect there to be a short-term cooling effect due to the light colored clouds produced by the volcano - but that effect can't last for more than a year - so the longer term effect can only be to contribute to global warming. SteveBaker (talk) 01:15, 25 April 2010 (UTC)

Stratified Italian soda + cold cream => Salt fingers??

A fluid mechanics professor and myself are a bit stumped on this question:

Go to your local cafe, order an Italian soda. Make sure the barista/server pours the soda in very gently so that the syrup & soda remain as stratified as possible. Now get the carafe of cold half & half & pour in 1-2 tablespoons. The cream is significantly denser than the soda and sinks quickly. However, the syrup is denser than the cream and so the cream is stopped abruptly at the syrup/soda interface. (Side note: the breakdown of large -> small turbulent structures at this point is really cool!)

After ~10 seconds, small fingers of cream appear to drop into the syrup layer ... and look a LOT like salt fingers (see wiki article + links on those). Salt finger theory relies on the lower layer being cold and the upper layer being warm such that thermal diffusivity causes displacement instability (i.e. a bit of warm upper fluid is randomly displaced downward, quickly loses its heat to the ambient cold layer, and continues to fall downward because its density just increased through loss of heat).

In the case of the Italian soda, the cream (upper layer) is COLD and the syrup (lower layer) is warm/room temperature. This SHOULD be a STABLE configuration provided that the syrup is indeed denser than the cream, because any parcel of fluid that falls into the syrup should get warmer, lose density, and rise back to the point of equilibrium. Yet these fingers clearly fall into the syrup.

I thus present this conundrum to the reference desk. I highly recommend you try it!

128.193.45.125 (talk) 20:46, 24 April 2010 (UTC)

I'm afraid I haven't been able to get you a complete answer. Poking around the web, I find these figures for the specific gravity (density) of

• Half and half: 1.031 g/cc at 4.4°C, and 1.024 g/cc at 20.0°C;
• Pure water: 1.000 g/cc at 4°C, and 0.998 g/cc at 20°C;
• The densities for the flavor syrups will depend on the manufacturer and the particular syrup. For Torani brand, there appears to be between 15 and 23 grams of sugar per 30 mL (1 fluid ounce) serving; you'll have to find the tabulated densities for sucrose solutions (the primary contribution to the sugars is cane sugar: sucrose.

Hopefully you'll find what you're looking for. TenOfAllTrades(talk) 21:30, 24 April 2010 (UTC)

Here's my guess: the syrup curdles the cream, creating globules (curds) that are denser and therefore fall into the syrup until the density finds an appropriate equilibrium. Any chemists out there know if syrups are acidic enough to do this?128.193.45.125 (talk) 22:11, 24 April 2010 (UTC)

You might be right - but I suppose there is another possibility. I suspect that the syrup and the cream are very similar in density - with the cream being very slightly the denser. As the cream descends through the liquid, the density gradient will reduce the downward force on the cream to the point where there isn't enough density difference to provide a force that will overcome the viscosity of the liquid. Hence, I'd expect the cream to stop moving just before it's at the right density level. What we have now is a slightly unstable situation - but without enough energy in the overall liquid to overcome the viscosity barrier. But there is still small-scale random motion going on - so it's only a matter of time when two or three streams of liquid flow that happen to be heading in the same direction join and together provide enough energy to overcome the viscosity of the syrup. Hence, the cream breaks through in these "fingers" that appear more or less at random. Once they get started, they can be self-sustaining and will eventually allow the cream to flow to the very bottom.

It would be interesting to get an accurate measure of the densities of syrup and cream...but because either can absorb water and other 'stuff' in this complex mixture, it may be that they absorb other parts of the liquid at different rates. Any system as complex as this is going to be very tough to analyse.

SteveBaker (talk) 00:32, 25 April 2010 (UTC)

Salt fingers require Double diffusive convection. You have to consider both the diffusion of the heat and the diffusion of salt (or sugar in this case). These problems are not trivial even with knowing all the properties of all the components. I went to a course on DDC (and started the Wikipedia article on it) but it was too long ago. --BozMo talk 19:55, 26 April 2010 (UTC)

First human

This may sound oversimplified, but evolutionarily speaking, would the mother of the first homo sapien have been a different species than her offspring? Spellcast (talk) 20:49, 24 April 2010 (UTC)

Strictly speaking no. Because to breed, both parents would need to be of the same species in order to produces fertile offspring. Yet, I have this feeling that some one will post... Yeah But !... --Aspro (talk) 22:14, 24 April 2010 (UTC)

Here is the Yes But bit Neanderthal#Interbreeding_hypotheses. --Aspro (talk) 22:24, 24 April 2010 (UTC)

Yeah but "able to reproduce with fertile offspring" isn't really a satisfactory definition of species. See Species#Definitions_of_species for 14 different definitions of what constitutes a species, of which "fertile offspring" is just one. Most of these definitions would say that the mother was indeed the same species as her child, assuming that she was pretty much like her child in most respects. Which would make the child not the first homo sapien, leading to a paradox. Conclusion: there is no single definition of what exactly constitutes a species, and you have to be comfortable with some blurry boundaries between one species and another. Staecker (talk) 22:41, 24 April 2010 (UTC)

Species is a fuzzy, fluid concept, so there's really no point in trying to establish a final cut-off on who was human and who was just a dirty ape. Vranak (talk)

Interesting argument by Dawkins here Count Iblis (talk) 23:21, 24 April 2010 (UTC)

Ah yes, I'm glad you linked to that interesting article, which I now recall reading years ago. Dawkins' mention of ring species is quite useful in applying here. Spellcast (talk) 01:30, 25 April 2010 (UTC)

Yes, an excellent article by Dawkins. Thanks Count Iblis. It reinforces the notion that a new or different species is identified in retrospect rather than at its first appearance. When a number of creatures are determined to be different to other similar creatures we say they represent separate species of the same genus. It won't necessarily be unambiguous so there is likely to be learned debate about where the boundary lies between the two species. (Genetically, there are millions of differences within any one species.) There is also likely to be speculation about how many thousands of years ago the two species diverged. It certainly won't be possible for the mother of a new-born to say Whoops, I've given birth to the first member of a new species. Dolphin (t) 07:00, 25 April 2010 (UTC)

If we had a solid definition of what is a human - some kind of a bright-line measurement (or set of measurements) - then you could say that the mother of "the first human" was (by definition) not human. However, we don't have a measurement like that. When we look back through the hominid fossil record, we see slow, continuous, change from something that's clearly an ape-like non-human to something that clearly is human with perhaps a couple of million years between those two fossils. We cannot put a stake in the ground and say that at on April 12th on 2123456 BC there was a sudden change between the "obviously not human" and the "obviously human" in the fossil record.

Evolution isn't like that...well, mostly it's not like that. If we look at a specific attribute of what makes us what we are, there are abrupt changes. The one I usually trot out at times like this is the evolution of lactose-tolerance in adults. There is a very specific change on chromosome 2 that flips a switch between lactose tolerance and lactose intolerance - there is no halfway house here. You are either one or the other. So we know for sure that the first lactose-tolerant human child was born of a lactose-intolerant human mother (probably around 4,000 to 6,000 years ago in some part of the world where people started to farm sheep and goats on a large scale).

So if you found some single, special feature of humanity that was controlled by an "on/off" gene like that - then you'd be able to point to that specific baby that had that specific gene and say "definitely human" - and to the mother of that baby and say "definitely not human". But we don't have such a specific gene...if we did, we'd probably be able to point to a specific skull in a long line of them in a museum someplace - and say "that one is human - that one isn't" - but we can't do that, so there is no single gene that we've chosen to mean "human" or "non-human".

That's not to say that we couldn't do that - we could look at our nearest relatives (chimps, gorillas, etc) - find a gene that we have that the chimps and gorillas don't have - and label that "the human gene". But doing that would be extremely controversial. Suppose we picked a particular gene on the long arm of chromosome 7. A child born with a rare genetic condition called "Williams disease" might well be missing that gene. Are we then going to label that child "not-human"? Of course not! But if we picked a bright-line definition of "human" then this kind of thing would happen all the time. I don't think we have the cold-hearted scientific rigor to do something like that.

Our modern definition of "human" is something like "born of a human mother" (although "born from an egg produced by a human mother" might be a better choice if we were to develop artificial wombs or something in the future). But that definition leaves us with a very definite "chicken and egg" problem.

So we have to accept that "humanity" isn't a black-and-white thing. There have been animals around in the past that have been "almost human" and others that are "somewhat human" - but nowhere has there been a step where a "definitely not human" gave birth to a "definitely human" child. What happened was that a "49.9% human" mother gave birth to a "50.1% human" child, the child looked, behaved and performed more or less identically to his/her brothers and sisters - looked like his/her mommy - maybe was slightly better at the "walking upright" thing - maybe fractionally more intelligent - maybe a tad less hairy...but not so much that you'd notice.

In the end, like so many RD:Science questions, this is not about science - it's about the definition of a word. What the OP is asking is a matter of linguistics. I recommend reading Chicken or the egg - an odd article - but actually very meaningful in the context of this question.

SteveBaker (talk) 00:13, 25 April 2010 (UTC)

Since lactose tolerance in adulthood is determined by a single gene, as you say, it probably occurred multiple times spontaneously, which complicates it. --Tango (talk) 01:13, 26 April 2010 (UTC)

The current evidence is unclear but it's possible only one lactase persistence mutation persisted, see Lactose intolerance#History of genetic prevalence and also [5] [6] [7]. Nil Einne (talk) 14:26, 26 April 2010 (UTC)

I think Tango was (pedantically) commenting on Steve's statement that the first lactose tolerant person was born while people were farming goats for milk. Since it (ie lactose tolerance) is determined by a single gene, it quite likely randomly came up at a previous time when there wouldn't have been any selective pressure to support it. 41.213.125.249 (talk) 15:17, 26 April 2010 (UTC)

See http://www.onelook.com/?w=homo+sapiens&ls=a. - Wavelength (talk) 00:25, 25 April 2010 (UTC)

...and in what way does that help? All of those dictionaries say things like "The primate species of mammal to which modern humans belong. Homo sapiens is Latin for knowing man or wise man."...but that completely fails to draw a bright line between this species and other, older species. It also fails in that the word "species" is a totally fuzzy, inadequate term. There is nothing in any of these definitions that would allow you to say "This creature is a human...that one isn't"...and that's what it would take in order to provide a "Yes" answer to our OP's question. Without such a 'bright line' definition (which would undoubtedly have to be genetic in order to be useful) - the answer is a clear "No" - there is no small step along the way from ape to human at which you could say that the mother was non-human and the child was human. SteveBaker (talk) 06:59, 25 April 2010 (UTC)

While there have been good answers, no one has linked to Speciation which discusses the general concept. Nil Einne (talk) 16:29, 25 April 2010 (UTC)

The question is invalid, like the one about chicken and egg (you can find that article on Wikipedia, too). Also consider that the brown bear and the polar bear routinely mate in the wild, when they are obviously on diverging evolutionary paths. Imagine Reason (talk) 11:52, 26 April 2010 (UTC)

Indeed - and if you need an example that's from a pair of animals that have diverged a little further than that, consider the situation with horses and donkeys (which produce mules) and between lions and tigers (which produce tigons and ligars). In those cases, the divergence produces offspring that are generally infertile. (I believe the offspring of brown and polar bears are fully fertile). As divergence increases still further, producing live offspring from mating becomes impossible - and with yet more divergence, even mating becomes impossible. Like so many things in biology, there is a rather smooth/continuous variation between "same species" and "different species" and coming up with useful, firm definitions for words like "human" and "species" is impossible. SteveBaker (talk) 12:36, 26 April 2010 (UTC)

And you have the "humanzee", the mythical human-ape hybrid- In 2008 a Scottish scientist wanted to give it a try [8]. Ethical problems abound. From the last link "The Human Fertilisation and Embryo Bill prohibits the placement of animal sperm into a woman The reverse is not prohibited. It's not even mentioned.".

We don't an article on blynxes, a hybrid of bobcat and lynx: "In 2003, DNA analysis confirmed that five odd-looking felines found in Maine and Minnesota were bobcat-lynx hybrids, dubbed blynxes."[9] --Enric Naval (talk) 15:54, 26 April 2010 (UTC)

A better latter link would be to Canadian lynx (Lynx canadensis), since the bare 'linx' links (ha!) to the Genus, which of course includes the bobcat (Lynx rufus). 87.81.230.195 (talk) 20:15, 26 April 2010 (UTC)