Wikipedia:Reference desk/Archives/Science/2019 November 4

= November 4 =

Smallest animal with red blood
Which is the smallest animal which has red blood along with bones — Preceding unsigned comment added by 42.110.198.41 (talk) 06:21, 4 November 2019 (UTC)


 * I understand that fish have red blood, with a few exceptions, so look at our list of smallest fish for some possible contenders for the title. SinisterLefty (talk) 06:41, 4 November 2019 (UTC)


 * The smallest vertebrate, according to Wikipedia, is the tiny frog Paedophryne amauensis. The article doesn't address whether it has red blood, but nearly all vertebrates do, so that seems likely.  Dragons flight (talk) 10:36, 4 November 2019 (UTC)


 * The frog may be slightly shorter, on average, but some of the fish in the list above appear to have the lower volume/mass/weight. SinisterLefty (talk) 14:20, 4 November 2019 (UTC)
 * Cochineal?--Shantavira|feed me 17:19, 4 November 2019 (UTC)


 * I don't think that's blood per se (insects don't have circulatory systems), and of course cochineal isn't a vertebrate. --jpgordon&#x1d122;&#x1d106; &#x1D110;&#x1d107; 17:30, 4 November 2019 (UTC)
 * Hmmm? -- Jayron 32 19:00, 4 November 2019 (UTC)


 * That link says it's more like lymph than blood. SinisterLefty (talk) 21:23, 4 November 2019 (UTC)


 * That link says that there's a circulatory system, which contradicts the statement "insects don't have circulatory systems". The problematic statement wasn't "I don't think that's blood per se", which is correct, it isn't blood, it's hemolymph.  However, insects do have a circulatory system that pumps the substance around their bodies.  -- Jayron 32 12:07, 5 November 2019 (UTC)


 * Thanks for the clarification. However, it would be helpful if you initial responses would be clearer. SinisterLefty (talk) 14:33, 5 November 2019 (UTC)


 * Fair point. I will work harder to be a better person in the future.  -- Jayron 32 14:35, 5 November 2019 (UTC)


 * Cochineal don't have blood or bones. "The insect produces carminic acid that deters predation by other insects. Carminic acid, typically 17-24% of dried insects' weight, can be extracted from the body and eggs, then mixed with aluminium or calcium salts to make carmine dye, also known as cochineal". Richerman  (talk) 17:37, 4 November 2019 (UTC)
 * I squished a couple a week ago. It sure leaves a nice stain on the skin. --jpgordon&#x1d122;&#x1d106; &#x1D110;&#x1d107; 17:46, 4 November 2019 (UTC)
 * Are there smaller ones with red blood and no bones? Sagittarian Milky Way (talk) 19:09, 4 November 2019 (UTC)ll
 * Earthworms have hemoglobin in their circulatory system, and so have red blood. Not all annelids use hemoglobin, some use chlorocruorin, which isn't red (it's amazing how a small change to the conjugated pi system can have such a drastic change in color). Some echinoderms have hemoglobin as well, at least sea cucumbers. --OuroborosCobra (talk) 21:42, 4 November 2019 (UTC)
 * Apparently planorbidae, unlike other mollusks, also have hemoglobin, and red blood, as opposed to green copper based blood. Several forms of crustaceans use hemoglobin. I would bet there is where you will find the smallest organisms with red blood. --OuroborosCobra (talk) 21:49, 4 November 2019 (UTC)

Offsprings and mutations
I've heard a concern which says that because insects on average produce more offsprings than many other mammals, including humans, their adaptive radiation should have progressed faster due to higher probability of mutations in every generation. Yet, despite their species diversity, the insects remained basically the same on average as they were millions years ago whereas most mammals evolved noticeably faster despite less offsprings (in case of human evolution, on the order of "some 15–20 million years ago" starting from the divergence of the Hominidae). The number of orders in insects also stays roughly similar to that of mammals (around 30 vs 26). Why is that? Thanks. 212.180.235.46 (talk) 17:33, 4 November 2019 (UTC)
 * why do you say that "insects remained basically the same"? Because a few insect species you know (that is, very successful) appeared long ago? Rest assured that quite a number were wiped out. Or because the differences between, say, a Macrotermes and a Nasutitermes mean less to you that the difference between, say, a chimpanzee and a gorilla?
 * see also: Evolution of insects
 * The number of order is not relevant, there are so much more species in each order of insects that in orders of mammals Gem fr (talk) 18:25, 4 November 2019 (UTC)


 * Humans are still far from knowing all species. Especially small species like Insects are often overlooked and unknown ones are frequently revealed, simply because anyone would report a "new" 4 m high ape species but hardly anyone would even notice an unknown 0,2 mm ant. --Kharon (talk) 20:56, 4 November 2019 (UTC)
 * Note that morphology similarity does not denote biochemical similarity. So-called "living fossils" such as the pycnopodia have preserved their structure, but it is more than likely that the biochemistry changed, to ward off parasites if nothing else. Take for example the jellyfish in "Jellyfish Lake": the lack of evolutionary pressure to produce venom gave advantage to those that invested less in venom production. The result may look similar to other species, but the biochemistry went a long way. אילן שמעוני (talk) 11:43, 6 November 2019 (UTC)


 * The rate of mutation is independent of the taxa or of any life history character. All life has basically the same rate of mutation, dependent only on the passage of time. See Molecular clock. Abductive  (reasoning) 05:04, 7 November 2019 (UTC)


 * That's not exactly true. See mutation rate. The genetics influence the mutation rate, along with the environment. For a single organism the mutation rate does tend to average out, over time. Organisms that have many offspring can tolerate more defective offspring, in order to increase the chances of a helpful mutation, so will generally be genetically predisposed to a have higher mutation rates. SinisterLefty (talk) 05:11, 7 November 2019 (UTC)

Tree(g) numberphile video
In a recent numberphile video "Tree vs Graham's number", rates of growth of series are compared to a hierarchy of functions called f0(x) defined as x+1 and then fn(x) defined by applying f{n-1} x times.

Do these functions have a name that I could look up?

2A01:E34:EF5E:4640:6450:7CCB:76D1:CFE1 (talk) 17:53, 4 November 2019 (UTC)
 * Consult large numbers and Names of large numbers Gem fr (talk) 18:05, 4 November 2019 (UTC)
 * found it by indirection from that article: Grzegorczyk hierarchy. Thanks.
 * 2A01:E34:EF5E:4640:6450:7CCB:76D1:CFE1 (talk) 19:23, 4 November 2019 (UTC)
 * TREE probably refers to the function described at Kruskal's tree theorem. 173.228.123.207 (talk) 11:36, 7 November 2019 (UTC)

What is the accuracy of a lodestone on a string or a temporarily magnetized needle floating in a cup at different Earth field strengths?
Are these sensitive enough to show magnetic north till magnetic reversal temporarily causes more than two poles? I've made a non-magnetic needle work by rubbing it 100 times in the same direction with a small and weak permanent magnet, how much could Earth's field weaken before you'd need a stronger magnet, longer pointer or a more magnetizable material? Sagittarian Milky Way (talk) 18:23, 4 November 2019 (UTC)
 * It works fairly well. I am a science teacher who sometimes teaches a class called "Physical Science" where we discuss magnetism at some point.  I have, for years, had a magnet hanging from a string attached to my ceiling.  It has been pointing at magnetic North for at least 6 years at this point.  At no time has it suddenly stopped pointing north.  In general, any magnet will, if properly suspended and without too much friction to overcome, align itself with the local magnetic field and will point at magnetic north.  In a frictionless (ideal) environment, every magnet will align itself with the magnetic field; it is only when friction prevents it that it doesn't.  -- Jayron 32 18:56, 4 November 2019 (UTC)


 * Also note that the magnetic north pole isn't exactly at the geometric north pole, and it also moves around and isn't exactly on the opposite side of the Earth from the magnetic south. So, all magnetic compasses could be off at some time in the future, prior to magnetic reversal. To some extent, we can compensate for the difference between magnetic north and true north (or the two south poles) if we know approximately where on Earth we are. Of course, these days we have many other options to use satellites and such, so putting too much effort into regularly adjusting magnetic compasses may not make sense. SinisterLefty (talk) 21:13, 4 November 2019 (UTC)
 * If the friction was low enough for it to not get stuck off azimuth your compass wouldn't be off, your map's declination would be. Sagittarian Milky Way (talk) 21:43, 4 November 2019 (UTC)


 * Lodestones were not widely used directly for making a compass. For one thing, they were too expensive to travel with. More commonly, a steel compass needle would be magetised with a lodestone in a workshop, then that would be used.  This was also lighter, so responded more quickly to movement.  Although you can use a suspended lodestone as a compass, they're very inconvenient on any sort of moving ship - mass and inertia swamps the magnetic effects.
 * It was recognised early on that iron and steel behaved differently as magnets, see remanence. An iron compass needle worked fine, but would lose its magnetism over a voyage (some well-funded ships carried a lodestone, and could use this to restore the magnetisation). This was even seen as a test of the quality of the steel. The traditional association of compasses and needles comes about not just from their shape, but because a sewing needle was often the only commonly available source of high-quality steel with good remanence, and they were also a convenient size and shape.
 * For a static compass, such as in surveying, a weakly magnetised needle will eventually settle. For use on ship, the more magnetic field it can produce gives more restoring torque, thus less sensitivity to interference from movement. Andy Dingley (talk) 11:14, 5 November 2019 (UTC)