Wikipedia:Reference desk/Archives/Science/2013 October 7

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October 7

Fossils in antartica

Are there human fossils or gorilla fossils that have been found in antarctica? How about ruins? — Preceding unsigned comment added by 128.214.166.6 (talk) 09:10, 7 October 2013 (UTC)

No, Antarctica's geographical isolation and glaciation predates humanity's existence. Plasmic Physics (talk) 09:32, 7 October 2013 (UTC)

Elder Things, though—that's a different matter. Deor (talk) 09:59, 7 October 2013 (UTC)

Scarely any more credible that the fictious scribblings on those hellish Archaean organisms is the real Piri Reis map which - if you squint your eyes just so and really really believe - shows a prehistoric Antarctic coast, free of ice, and full, perhaps, of ancient astronauts and maybe Elvis. I mention this only because there are occasional "documentaries" about this, which may linger in the back of one's mind. -- Finlay McWalterჷTalk 11:52, 7 October 2013 (UTC)

Let's take this Q a step at a time:

1) Will there be any fossils in Antarctica ? Yes, because it was once a lush tropical land, in the era of dinosaurs.

2) Will there be any primate fossils ? No, as noted above, because Antarctica was much as it is now during the era of primates, and thus not suitable for primates. However, there might be human mummies, of early explorers, whalers, etc., who died there and were freeze dried.

3) Will there be many accessible fossils ? No, because of the conditions in Antarctica now. Most of it is covered by steadily moving glaciers, making it quite difficult to dig through. There are occasional rock outcrops, though, and excavation could occur there, however, the weather and distance still makes any such mission rather difficult and expensive.

4) Will those fossils be more accessible in the future ? Sure, due to improved technology, perhaps allowing us to scan and find fossils before we start to dig, and also maybe due to global warming, which may melt off some of the glaciers in the way. StuRat (talk) 12:01, 7 October 2013 (UTC)

The British Antarctic Survey website has a database of Antarctic fossils, including some pictures. 'Abundant finds of fossil leaves and wood point to the existence of extensive forestation in earlier geological periods, even to within a few degrees of latitude of the South Pole itself. Dinosaurs, and later, marsupial mammals once roamed across its surface.' AndrewWTaylor (talk) 12:36, 7 October 2013 (UTC)

Note that this doesn't mean the dinos lived within a few degrees of the South Pole, as Antarctica has moved over time, as all the continents have, due to continental drift. StuRat (talk) 12:50, 7 October 2013 (UTC)

See also Geology of Antarctica. Count Iblis (talk) 13:55, 7 October 2013 (UTC)

• Actually the ice cover of Antarctica only dates back about 15 million years, while primates first appeared around 50 million years ago -- so time alone is not decisive here. But Antarctica split off from Africa around 150 million years ago, and its most recent linkages are with Australia and South America. Like Australia, its isolation caused it to never gain land mammals more advanced than marsupials. Looie496 (talk) 16:26, 7 October 2013 (UTC)

• "...OTHER than mammals" may be better language. Words such as "advanced" are problematic when speaking of evolution. And of course the marsupials in Australia continued to evolve after their separation from those places where non-marsupials evolved. HiLo48 (talk) 22:22, 7 October 2013 (UTC)

Yes, the platyrrhine monkeys originated in South America 40 million y/a. It is possible they colonized Antarctica. μηδείς (talk) 16:47, 7 October 2013 (UTC)

What's the likelihood of a disease occuring by means of a french kiss?

What's the likelihood of a disease occuring by means of a french kiss? 140.254.70.33 (talk) 20:47, 7 October 2013 (UTC)

Depends on the disease and the contact. If you've got a specific concern, see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:17, 7 October 2013 (UTC)

Oral ecology and more specifically diseases transmitted through Saliva have a partial answer. 23:05, 7 October 2013 (UTC)

Note that diseases can be transmitted from one person to another by kissing, but the act of kissing doesn't create the disease. A person has to be carrying the infection in order to pass it to someone else. thx1138 (talk) 16:11, 8 October 2013 (UTC)

Could we eat grass?

Can we process (break it down) cellulose to make it edible for humans? OsmanRF34 (talk) 22:01, 7 October 2013 (UTC)

No. People eat it when they are starving because it is filling, but you cannot survive on it. See Irish potato famine. μηδείς (talk) 22:30, 7 October 2013 (UTC)

Medeis, I mean could we eat it, after we have processed it biochemically (with some enzyme, bacteria or whatever) outside our body. OsmanRF34 (talk) 22:53, 7 October 2013 (UTC)

(ec) Cellulose is broken down by bacteria in our hindgut, but to a very limited extent. Humans have an ensyme that helps break down starch into sugars, so we derive nutrition from starchy foods. However, humans lack an ensyme to break down cellulose into sugars. In general, animals that can derive nutrition from cellulose are either monogastric using Hindgut fermentation, or ruminants. Cellulose structure does not change in cooking, either. If you were to "digest" cellulose outside the body, using some microorganisms such as Weizmann organism for example, you'd end up with sugar or alcohol molecules (some of which have, indeed, substantial nutritional value).--Dr Dima (talk) 22:34, 7 October 2013 (UTC)

The best way to process grass chemically is with a cow. Fermented cellulose yields wood alcohol, which is poisonous. The problem is you either run into toxins or huge waste--otherwise people would be doing it now, rather than feeding it to their livestock. μηδείς (talk) 23:07, 7 October 2013 (UTC)

And using bacteria to break down cellulose is one method of producing methanol now under research and development. The hope is to provide a car fuel by using farm waste, without the downside of making food more expensive, which happens when you make ethanol from corn, or any other food. StuRat (talk) 00:00, 8 October 2013 (UTC)

No, Medeis, the cow is not the best way to process grass. In fact, it takes 20 pounds of grass (or 7 pounds of feed) to make 1 pound of beef; see Environmental impact of meat production. Most of the grass / feed is wasted as CO2 and methane of cow respiration and flatulence. I cannot find numbers for how much sugar or ethanol can be made out of a given amount of straw or grass, but I really hope the ratio is higher than 1:20. (I'm aware it's not an entirely fair comparison, though, as there are large additional costs involved in both beef and bio-ethanol production). In any case, the grass is not meant for eating; it is meant for playing soccer :) . If you want a better intermediate between sunlight and food, try spirulina. --Dr Dima (talk) 00:20, 8 October 2013 (UTC)

Okay Dima, you can recommend eating fried termites rather than some bovine equivalent if you like, but neither does Spirulina 'eat' grass. In the meantime, I will take my grassfedcowproducts. μηδείς (talk) 00:30, 8 October 2013 (UTC)

I don't think that 20:1 ratio is relevant. It's the calories in the 20 pounds of grass that should be compared with the calories in the pound of beef, not the weight. Or perhaps we could compare the protein or some other nutrient. Now, I agree that feeding cattle with food that humans can eat directly is a poor choice, in comparison with feeding that food directly to the people, but in the case of grass, using animals to convert it into something edible to humans, like milk or meat, isn't a bad choice. Of course, we can choose to grow food crops instead of grass, in some places, but not all places where grass grows are suitable for other crops. StuRat (talk) 00:27, 8 October 2013 (UTC)

You both are certainly right in that beef provides more calories (than grass) and tastes much better than the alternatives; I am not arguing for switching from eating steaks to eating sugar, ethanol, or cyanobacteria :) I do however think that, as far as the answer to the original question goes, fermentation outside the cow is a more promising method of cellulose processing than fermentation inside the cow. --Dr Dima (talk) 00:56, 8 October 2013 (UTC)

Grass carp are much more efficient than cattle for converting cellulose to human-edible nutrients. Roger (Dodger67) (talk) 09:09, 8 October 2013 (UTC)

People might have a beef with that and carp about your plan. StuRat (talk) 14:03, 8 October 2013 (UTC)

Can we process (break it down) cellulose to make it edible for humans?

Yes, in theory. And there are rudimentary efforts to develop an efficient chemical process to convert cellulose to starch for human consumption, as discussed in this paper (non-technical overview: Let Them Eat Wood!). The process though is currently wildly uneconomical:

Zhang estimates that, given the current price tag of the enzymes that his team used, it would cost about $1 million to turn 200 kilograms of crude cellulose into 20 kilograms of starch, about enough to feed one person's carbohydrate needs for 80 days.

Also note that while using cellulose as a food substitute is improbable in the near future, cellulose is already used extensively as an "external energy source" after conversion to Cellulosic ethanol. Abecedare (talk) 01:14, 8 October 2013 (UTC)

I think "extensively" is a bit of an exaggeration when talking about Cellulosic ethanol. Rmhermen (talk) 01:39, 8 October 2013 (UTC)

You are right. I should have said that it is much closer to mass commercial exploitation than cellulose-derived-food but had a brain freeze at some point. :) Abecedare (talk) 02:37, 8 October 2013 (UTC)

Yes, I had mentioned this above. Note that this could increase food production, indirectly, if we return to using corn exclusively as food and cattle feed, rather than to produce ethanol. StuRat (talk) 14:01, 8 October 2013 (UTC)

Many animals besides cattle convert cellulose into tasty meat, and some produce milk and textiles as well. Rabbits eat a lot of grass and other plants and need less management than cattle. I have several in my yard most days managing their own affairs quite well. Edison (talk) 14:36, 8 October 2013 (UTC)

Yes, but try catching them and eating them. First, I bet it will be harder than you think. Second, after you catch 1 or 2, you might find the rest move elsewhere. So, if you actually want to use rabbits as a food source, you would likely need to keep them in cages, which is at least as much work as managing a cattle herd. StuRat (talk) 12:15, 10 October 2013 (UTC)

Brain wrinkles

Why are our brains wrinkled? The standard explanation is that it's to do with size- but this doesn't make sense. Doesn't volume matter more than surface area for the brain? Is there some kind of neural activity that can only take place on the surface? 68.0.144.214 (talk) 23:11, 7 October 2013 (UTC)

[1] Plasmic Physics (talk) 23:18, 7 October 2013 (UTC)

Completely SWAG here: more surface (which implies less volumen), and that's helpful because it can get more glucose or oxygen. OsmanRF34 (talk) 23:29, 7 October 2013 (UTC)

• The appropriate (if not helpful) articles here are gyrus and sulcus. The size explanation does make sense, you just have to see it from an evolutionary/developmental point of view. It's specifically the outer layer of the brain, the neocortex, which expanded the most during human (and other higher mammals) evolution. The embryonic development here is important, like all mammals, the cortex develops in a flat, layered structure during early embryogenesis. The thickness and order of these layers is crucial for the correct functioning of the cortex later on. This is why you can't just make them thicker, rather than fold them up. In lissencephalic animals, the cortex remains flat. In humans however, by the 5th month, the cortex grows too large to remain in a flat layer, in essence it outstrips the growth of the underlying deeper brain structures. Hence the giri and sulci, just a means to fit an excessively large neocortex in a finite volume of skull, without distorting the organisation within the cortex. Fgf10 (talk) 23:39, 7 October 2013 (UTC)

• Surface and volume both matter, but in different ways. The cerebral cortex consists of gray matter on the surface and white matter underneath. The cell bodies of neurons are almost entirely in the surface layer of gray matter, and there is no way of making that layer thicker without massively changing its architecture. So the only simple way to increase the number of neurons is to increase the surface area. The white matter is mainly filled with axons that connect neurons to each other. So, an increase in connectivity would generally imply an increase in white matter, and therefore an increase in volume. The factors that result from all this are pretty complex to work out, but if you would like to read more, you might look at http://www.pnas.org/content/97/10/5621.full for a starting point. Looie496 (talk) 23:42, 7 October 2013 (UTC)

Brains of several types of mammals, with labels in French

• How do you fit a cloth napkin into a wineglass? μηδείς (talk) 00:33, 8 October 2013 (UTC)

Make the napkin smaller than the wineglass, of course. That rationale isn't convincing unless you explain why the napkin needs to be larger than the wineglass. For the cerebral cortex the answer isn't obvious, because the general principle is that the cortex of small-bodied animals such as a rat tend to be smooth, whereas the cortex of large-bodied animals such as a whale or elephant tend to be very convoluted. Looie496 (talk) 01:17, 8 October 2013 (UTC)

Does it not occur to you that making the neocortex smaller means making the processing area less powerful? The chimp's cortex is about 1/4 the surface area of ours, and the difference is largel due to wrinkling. Human brains have a mechanically limited volume, and folding allows more surface within the same volume. The surface structure of the cortex is vital. Jeff Hawkins covers this in On Intelligence. This is all comparative mammmalian intelligence 101, not speculation. Carl Sagan covered it way back in his Dragons of Eden. μηδείς (talk) 01:53, 8 October 2013 (UTC)

Human brain addresses the folding and gives the reason for it. As Fgf10 implies, we don't seem to have any one article that addresses this directly, fully, and concisely. μηδείς (talk) 02:49, 8 October 2013 (UTC)

Of course packing more surface area into a given volume is part of the story, but a full understanding would mean being able to explain the differences in convolution patterns for various species, as in the picture I've added. And that's not so easy to do. Looie496 (talk) 03:59, 8 October 2013 (UTC)

That PNAS reference is really a nice exposition, except.... it argues that a simple scaling law requires the amount of white matter to grow at a 4/3 power law faster than the amount of grey matter. Which means that if an animal were large enough, the existing grey matter ought to be stretched taut, doesn't it? Also, the humans are right dead center on the line they draw through all the species. [2] Which leads me to think that the convolutions actually have nothing at all to do with the grey/white matter ratio, at least within the existing range of sizes; they incorporate both white and grey, as we know from images. And yet... well, something has me badly confused on this point. Wnt (talk) 04:03, 8 October 2013 (UTC)

Hmmm, some more clues: Echidna helpfully points out that its brain is far more folded than that of the platypus, with a thinner grey matter layer; and lissencephaly mentions that some persons with the condition have 'near normal intelligence'. It represents a failure of neuronal migration, but with relatively trivial causes (viral infection). So what we're looking at here is a reorganization of the grey matter to make it thinner (but wider) that somehow is advantageous, which makes it fold up. Wnt (talk) 04:14, 8 October 2013 (UTC)

OK, [3] is a good one. It explains the conventional justification for increased folding with increased size: the head can't scale at the same rate as the body and still be feasible to hold up. So there's this pressure to have a number of grey matter cells proportional to the cells (and presumably sensory cells, muscle fibers, etc.) of the body, versus this other scaling law of grey/white matter. The result is that there are lineages that undergo lissencephaly with miniaturization (mice, marmosets). Then there are sirenians, which apparently have a tendency to this, especially manatees (but then again, those critters are ... not persuasively functional neurologically, as critters go). I didn't quickly find information in NCBI for the claim that lissencephalics can have normal intelligence; I found the claim from Wikipedia at [4] but it isn't clear in this context whether this refers to mild losses of folding as well as mild losses of intelligence. I'll leave this point open for now. Wnt (talk) 04:28, 8 October 2013 (UTC)