Wikipedia:Reference desk/Archives/Science/2016 January 12

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January 12

Intra-species violence

Which species is believed to be the most cruel to its own kind? (E.g. chimpanzees are known for genocidal behavior toward their own kind; lions sometimes kill their cubs; black widows and praying mantises eat their mates; any other examples?) 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 02:28, 12 January 2016 (UTC)

Adult crocodiles are known to eat other crocodiles, especially young crocs. In the case of males fighting for mates which can be quite fierce, including to the death, that's done by what are called Tournament species. Vespine (talk) 02:39, 12 January 2016 (UTC)

Thanks! So, of all these and other species, which is currently believed to have the highest level of intra-species violence? 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 02:41, 12 January 2016 (UTC)

I don't know how easy that's going to be to answer. There are animals that fight for territory and for mates, there are animals that perform Infanticide_(zoology), there are animals that eat their mate after courtship. I'm not sure there is any particular one that stands out more than any others. One thing to consider is that there is a very real limiting factor to being too aggressive and "killing" members of your own species, do it too much and you risk wiping your self out.. In that respect and really it should have been my 1st answer, THE species which is far and away the most cruel to its own kind is clearly homo sapiens. Vespine (talk) 04:03, 12 January 2016 (UTC)

I don't think so. Only a small portion of humans die of homicide. I'm sure that one of the categories listed above would have a higher rate of death from their own species. One other category is that some spiders, I think, eat their own mother alive. Although, if that is the "plan", not sure that it counts as cruelty, as it's functionally similar to salmon dying after spawning, to leave their bodies for the next generation to eat. Then there's birds which have two nestlings, and the strongest one kills the weaker. StuRat (talk) 04:28, 12 January 2016 (UTC)

Other examples of animals that have been observed killing their own species- rabbits, hippos, chickens, dolphins, dogs. Greglocock (talk) 05:37, 12 January 2016 (UTC)

To me, "cruel" is a human moral judgement that can't really be applied to the actions of non-humans. Your immune system is pretty "cruel" to pathogens. You're a nice big yummy salty meat bag, and you won't share even a little with them! --71.119.131.184 (talk) 05:48, 12 January 2016 (UTC)

Bingo. Animals do what they do by instinct. Pathogens and the immune system are not "cruel", they do what their DNA tells them to. With humans, aside from the occasional acts of the criminally insane, most violence against other humans is by choice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:08, 12 January 2016 (UTC)

• Also, I'm not sure (even if we could validly apply human morality to non-human animals, which has it's own sort of intellectual problems) we could quantify a concept like "cruelty". If we can't assign a numerical value to "cruelty" (what is zero cruelty? What is negative cruelty? What does it mean to be twice as cruel as something else; or 1.37 times as cruel, etc.), then concepts like "the most" are meaningless as well. --Jayron32 17:12, 12 January 2016 (UTC)

In the follow up, OP discusses violence. I think that concept is also nebulous, but slightly more objective than cruelty. We could in principle watch a bunch of animals and count up how often one makes another bleed, breaks a bone, blinds, etc. OP may be interested in watching elephant seals fighting, they do so rather violently and bloodily: [1]. Another animal that gets pretty rough is the hippo [2] (fair warning: both videos show graphic intra-species violence). So while we can't give any good scientific rationale for "most cruel" animal, I get the idea OP is basically looking for information/references on animals that often engage in bloody/damaging fights. Some animals, mostly insects, also get pretty violent during mating. For example, some dragonfly females take a lot of damage during copulation, as the male has all kinds of barbs and brushes that attempt to remove prior sperm and prevent future mating. Sometimes females end up with holes in their eyes or wings. Some info on that here [3], [4], [5]. A key factor influencing this violent mating is that many insects are semelparous, not itoparous, so as long as the female can manage to lay eggs, it doesn't matter much from an evolutionary perspective if she dies soon after. SemanticMantis (talk) 17:32, 12 January 2016 (UTC)

The argentine ant may be a candidate for species that kills the most individuals of its own species. In their introduced range (e.g. California), different colonies get along, because they are all closely related (a evolutionary bottleneck or founder effect). But in their native range (and some other places), each colony fights for territory with the neighbors on a nearly daily basis, with many outright deaths. Again, this works a bit different from an evolutionary perspective, mostly because the ants are eusocial, and have haplodiploid sex determination. This means that from the superorganism perspective, a bunch of workers/soldiers killing each other doesn't have the same impact as if mammalian species often fought to the death. This page [6] has some nice video and discussion of how/why some argentine ants fight a lot while others don't. SemanticMantis (talk) 17:39, 12 January 2016 (UTC)

Whether the argentine ant or another species, I think it's a fair guess that if you are trying to answer this question on the basis of the volume/proportion of members of the same species killed (and you disqualify microbes) ants are going to be your prime exemplars. I may be missing something obvious is marine life, but ants are definitely the most continuously warlike terrestrial creatures, by and large. Of course, as SM alludes to, species differentiation with Formicidae is a very nuanced issue, in a way rather pertinent to the OP's question; the degree to which warring populations constitute the same species is not always an easy issue to make a firm determination on. Snow ^{let's rap} 18:52, 13 January 2016 (UTC)

Wiktionary defines cruelty as "an indifference to suffering or positive pleasure in inflicting suffering.". At the very lowest levels of brain power found in animals like black widows and praying mantises - I don't think they have emotions like "indifference" or "pleasure" - and it's not particularly clear that their tiny victims can truly "suffer". I recall seeing a demonstration on TV of a house fly who's abdomen had been completely severed - and which was still eating some sugar water placed in front of it. It didn't seem like the fly was "suffering" despite this horrendous injury.

So this leaves us with two possible standards to meet:

1. Behavior which would be cruel if a human were to do it or to suffer from it.
2. Behavior which actually reflects cruelty on the behalf of the animal inflicting it.

It's easy to say that a black widow spider is unutterably cruel by eating it's mate right after intercourse - by human standards, that's quite spectacularly cruel. But neither the female nor the male spider expects anything different to happen - the female doesn't take pleasure and the male probably doesn't even understand the concept of pain. So by the standards of the spiders themselves, this wasn't "cruel" at all.

On the other hand, if a lion takes down a gazelle by gashing it with claws, forcing it to the ground and crushing it's windpipe until it suffocates...we know that the gazelle is indeed feeling pain at the time - and the lion is either indifferent or taking pleasure in the kill. So we'd be tempted to say that this was "cruel" - even from the perspective of the lion.

Yet we must be careful. Does the lion know that the gazelle is suffering? We humans would know that because we have empathy - but do we think that lions have empathy? The human brain has a specific set of cells called Mirror neurons - which fire both when we act and when we observe the same action performed by another. We literally 'feel' the pain in that gazelle. But those neurons have only been shown to exist in primates...and possibly (maybe) in some birds. If the lion doesn't have mirror neurons, then it doesn't feel what the gazelle is feeling - so how does it infer that there is suffering? If it can't infer the suffering, how can we say that it's taking pleasure in it? It's taking pleasure in having food - but it's not taking pleasure in the suffering. You could certainly argue that it's indifferent to the suffering - but not by choice - by biology.

Humans take cruelty to another level - in everything we do, we have full understanding of our ability to inflict suffering - and to empathize with the victim. We even try to take some measures to try to avoid it (eg by humanely killing animals for food). But it's hard to find any instance of a cruel-by-our-standards act in animals that we aren't also guilty of in some regard.

But even then, it's tough to measure. Many of us go through our entire lives without directly inflicting pain on anything with a sizeable brain - so are we to conclude that humanity as a whole is cruel just because some number of us are? 100% of lions take down gazelle cruelly - but probably only maybe 1% of humans have ever intentionally/cruelly killed something with a high level intelligence. So are we judging the average behavior of an entire species - or the most cruel individuals - or the least cruel?

Because of the mirror-neuron thing - I think it's entirely unreasonable to attach the term "cruelty" to non-primates. So now we're down to humans, moneys, apes, lemurs and so forth. Certainly chimps are not beyond hunting down and killing monkeys by tearing them limb from limb while still alive. Equipped with mirror neurons, they ought to be wondering how the monkey feels about that - and their thoughts on the subject ought to be pretty similar to humans. But I think it would be hard to find chimpanzees who'd be prepared to perform cruelty on the scale that (some) humans do.

SteveBaker (talk) 18:09, 12 January 2016 (UTC)

Most of your discussion seems to be about interspecific conflict, while OP is interested in conflict between individuals of the same species. SemanticMantis (talk) 20:04, 12 January 2016 (UTC)

It was a simpler statement that way - however, the same arguments surrounding what constitutes "cruelty" in non-humans, and the lack of mirror neurons in non-primates - applies to intra-species as well as inter-species violence. SteveBaker (talk) 14:50, 13 January 2016 (UTC)

Well, mirror neurons are not the only neurophysiological structures implicated in empathy, nor do we know that they are confined to primates. The general observation (going back to Darwin's The Expression of the Emotions in Man and Animal and continuing through the most contemporaneous behavioural and cognitive research) is that most mammals do possess some sense of empathy (or at least emotional/mental connection or attachment), though in many cases it may be only readily in evidence with regard to parents, offspring and/or mating partners. Still, many species have shown a propensity for expanding this circle of empathy to others, both within and even without their species, as humans do. Snow ^{let's rap} 19:04, 13 January 2016 (UTC)

Flies definitely have nocireceptors and are adverse to sensations likely to indicate damage to their bodily integrity. How much this resembles human pain is (like any issue surrounding variant perception) a deeply complicated empirical and philosophical issue. But I think it's probably safe to say they can "suffer" to some degree. Snow ^{let's rap} 18:52, 13 January 2016 (UTC)

• By the way, the mantis thing is mostly a myth. It is true that female mantises sometimes eat male mantises after sex, but that happens almost exclusively in captivity! Sexual cannibalism among mantises is rare in their natural environment, though there is one species (out of thousands) that seems to require it. Also males sometimes eat females, and that makes even less sense. See Mantis#Sexual_cannibalism, and some further info here [7] [8] [9]. SemanticMantis (talk) 20:04, 12 January 2016 (UTC)

Where sexual cannibalism does exist in species (normally where males do not survive the winter), there is a trade-off calculation. How much more likely is it that (a) the male will find another mate, and (b) how much more likely is it that if his only mate eats him, the extra nutrients will result in more healthy offspring than the chance that he might be lucky enough to mate with multiple females, and produce even more healthy offspring.

For example, the male mates with and allows the mother of her offspring to eat him. Given the bonus of protein and fat he provides, she produces 1,000 healthy eggs. Or, the male quickly escapes, and the female lays 450 not-so-healthy eggs. He repeats this, and mates with another female (if he is so lucky) who also produces 450 mediocre eggs, and escapes. He then dies from the first frost, before mating again. In that scenario, allowing oneself to be eaten is the better strategy. μηδείς (talk) 21:09, 12 January 2016 (UTC)

Aye, some of this is covered at nuptial gift, including evolutionary perspectives. While sexual cannibalism is a bit different, it's basically just a rather extreme nuptial gift in terms of evolution and maintenance of the behavior, provided that it is the female eating the male. SemanticMantis (talk) 22:42, 12 January 2016 (UTC)

Speaking of nuptial gifts, consider the recipients of this beauty. You Always Hurt the One You Love... Matt Deres (talk) 03:47, 13 January 2016 (UTC)

does degeneracy in antibonding orbitals (e.g. dichloromethane) affect reactivity?

A few years ago, an organic chemistry teaching lab professor told me one of the reasons dichloromethane is unsurprisingly unreactive is because of the symmetry (degeneracy) of the C-Cl antibonding orbitals (in addition to the fact that C-Cl bonds are hard to displace). That is, a component of dichloromethane's unreactivity (as opposed to chloroform or chloromethane) is its symmetry. I can't remember what he exactly told me, but years later in my mind, his explanation is somehow jumbled up in my mind as "the attacking nucleophile finds it hard to choose" (which antibonding orbital to attack). Of course, molecules can't really choose anything, but the overall impression I got in my mind is that degeneracy increases orbital energy (in antibonding orbitals), but decreases orbital energy in / stabilizes bonding orbitals. Years later, I'm not exactly sure what he meant, which makes it hard to find a reference for this phenomenon, so I can actually document it in dichloromethane. Is there actually any basis to my interpretation of what he said?

Unfortunately, looking at degenerate energy levels has a lot of matrix mechanics and linear algebra on eigenstates and such, but not a lot of explanations on how degeneracy affects the thermodynamics/kinetics of bond formation / bond-breaking.

I'm actually trying to improve an article here so help appreciated! Yanping Nora Soong (talk) 11:08, 12 January 2016 (UTC)

Am I right this is related to the phenomenon of avoided crossing and quantum resonance? Yanping Nora Soong (talk) 11:21, 12 January 2016 (UTC)

It's been a while since I studied things like this directly in organic chemistry, but IIRC, Bent's rule comes into play here somewhere, and researching "bent's rule" and "dichloromethane" brought up this article which discusses the situation in some detail. Maybe that will help... --Jayron32 00:21, 13 January 2016 (UTC)

Bent's rule is a succinct description of coulombic relationships in polyhalocarbons and similar molecules - just using the old orbital model. While I think it has a certain quick-and-dirty usefulness, this article in the same Web site describes what's actually going on. loupgarous (talk) 02:55, 13 January 2016 (UTC)

That article didn't really explain what was really going on, at least not to my ears. I mean, it seems to come down to an argument that p orbitals are "not real". If you want to explain that water is 104 degrees rather than 109, Bent's rule is one option; the other is the "lone pair". Is a lone pair more real than an orbital? All these things are just ways to try to approximate Schroedinger equation solutions without doing the math, because, well, you need to do serious number crunching to do the math, but nowadays I wonder how hard it would be to get us to just bite the bullet... you probably have enough processing power on a watch, right? There ought to be an app for that... :) Wnt (talk) 14:43, 14 January 2016 (UTC)

Why do dead bodies get swollen?

Why do after people die, their bodies get swollen? Is it true? and if so, Is it a physiological process? 92.249.70.153 (talk) 12:24, 12 January 2016 (UTC)

See Decomposition#Bloat. Mikenorton (talk) 12:39, 12 January 2016 (UTC)

Thank you, it's very interesting article. This step could take place in body alive or just in dead body? 92.249.70.153 (talk) 13:09, 12 January 2016 (UTC)

I'd think that the immune system and biological conditions of a living body would tend to keep such microbial populations in check while a human is alive. Otherwise, we'd all be bloated. --OuroborosCobra (talk) 14:17, 12 January 2016 (UTC)

That's basically what flatulence is (although the bacteria are eating food waste, not usually the body itself). Smurrayinchester 14:54, 12 January 2016 (UTC)

The type of bacteria which predominate in the body changes after death, with the body's chemistry. Of course, the immune system ceases to work after death, and with death, oxygen no longer is part of the human body's ecology. So aerobic organisms die off (both aerobic bacteria and human body cells) and anaerobic organisms multiply with nothing to stop them, as long as there is still tissue or fat to feed them. loupgarous (talk) 02:44, 13 January 2016 (UTC)

I believe that Herod the Great's body was decomposing before his death and Elizabeth I of England 's corpse actually exploded from bloat while lying in wait. --Dweller (talk) 15:05, 12 January 2016 (UTC)

The body of Pope Alexander VI(Rodrigo Borgia) is reputed to have decayed extremely quickly after his passing. According to our article Pope Alexander VI, "The next day the body was exhibited to the people and clergy of Rome, but was covered by an "old tapestry" ("antiquo tapete"), having become greatly disfigured by rapid decomposition. According to Raphael Volterrano: "It was a revolting scene to look at that deformed, blackened corpse, prodigiously swelled, and exhaling an infectious smell; his lips and nose were covered with brown drivel, his mouth was opened very widely, and his tongue, inflated by poison, fell out upon his chin; therefore no fanatic or devotee dared to kiss his feet or hands, as custom would have required."[54] The Venetian ambassador stated that the body was "the ugliest, most monstrous and horrible dead body that was ever seen, without any form or likeness of humanity.""

To answer the OP's question, this is a physiological process. After the human body dies, its chemistry changes. The metabolism of glucose and oxygen to power body cells ceases. The human body becomes anaerobic and a host for anaerobic bacteria, and fermentation of the body's dead tissue and fat causes gases to form within the body. As long as the dead body's skin remains intact, it swells as the gases of fermentation expand within the body. That's why dead bodies bloat. loupgarous (talk) 02:30, 13 January 2016 (UTC)

How do animal duels (clashing horns or others) and getting the female partners work?

When two male animals enter a duel, how does this work with getting a female?

Is the female around and she chooses the winner? The winner gets more territory, and the female is included? The female is around, but she doesn't choose? The losers get scared and keeps the distance towards the female owned by more powerful animals?--Bickeyboard (talk) 14:37, 12 January 2016 (UTC)

That depends on the animal. Since you talk about "clashing horns", I guess you might be thinking of deer or elk – our article Rut (mammalian reproduction) says that stags normally fight to establish dominance (if they live in herd) or territory (if they live more alone), and doesn't mention much about the females having a choice. In birds, the females watch the contests (which are competitive but not usually violent) and do chose mates - this is called a lek. Smurrayinchester 14:48, 12 January 2016 (UTC)

Lots of different ways, depending on the animal. See Bighorn_sheep#Social_structure_and_reproduction for at least three different ways males of the same species may attempt to secure a mate. SemanticMantis (talk) 17:43, 12 January 2016 (UTC)

More general information can be found by researching the following topics (both inside and outside Wikipedia): Alpha (ethology), Dominance hierarchy, and Sexual selection. --Jayron32 20:04, 12 January 2016 (UTC)

Fair warning, pay attention to the tags in the alpha article, the (at least two) deadlinks and general lack of good refs, and also note that the only recent research article cited that uses the alpha terminology is actually making the claim that alpha status is not as clear and important as previously thought in gorillas. The section on canines is (correctly) backpedaling away from using the alpha terminology for wolves. Long story short, the scientific basis for "alpha" designation in animal social groups has been continually eroding for over a decade now, and some ethologists advocate abandoning the term entirely due to the problems with it. Here's a key paper [10] that discusses (and rejects) the notion of an "alpha" wolf that asserts dominance by violence in wolf packs.

The Dominance hierarchy article is much better, and I'll just add that this theory is on strongest scientific ground when discussing the social insects. In many cases there, full physiological and mechanistic pathways leading from violence to worker sterility are understood, see here for a good overview in bumblebees: [11] SemanticMantis (talk) 20:15, 12 January 2016 (UTC)

Very good information there. I will note that Wikipedia is not the only source of information in the world, and no one will go to the OP's own house and prevent them from researching any term in sources outside of Wikipedia either. The quality of a Wikipedia article is hardly a reason to assume that no information exists in the world on a topic, and the OP is quite invited to read current research outside of Wikipedia, including the state of the concept of the "alpha" and the deprecation of the use of that term in the current academia. --Jayron32 20:21, 12 January 2016 (UTC)

Sure, and in light of that, I'll update my warning to say that all readers should be critical and wary of the "alpha" terminology, especially when searching outside WP. Scientific articles published since the 90s usually use the word with care and discussion of what it means, and why they think it should apply.

But quickly enough a web search can lead to something that seems to be about wolves but is really propaganda written by misogynists. For instance, here are some google hits for /alpha wolf/ [12] [13] that nobody should ever read, because the only information given on wolves is incorrect (and the rest is just pathetic).

Sorry for the derail, but the misuse and misapplication of the alpha concept can be intellectually dangerous, so I thought I should explain a little further. SemanticMantis (talk) 20:42, 12 January 2016 (UTC)

If really no one should ever read the articles, so why link to them? Anyway, I am aware that many people use real or imaginary social structures in the animal kingdom to justify their own "naturalness" of some human structures (as if humans should just mimic other species). Thanks for the information in any case though.Bickeyboard (talk) 22:55, 12 January 2016 (UTC)

Bickeyboard. Two solitary male muskox will do this even when there is no chance of mating. They have already left the herd, too young or old, to be able to win and get a mate. Very impressive to see. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 13:34, 13 January 2016 (UTC)

Thanks for asking, I think this is actually very important. I linked the articles because this is a reference desk, and I believe that we should all strive to support our assertions with references when responding to questions. In this case, I wanted to support my claim that searching for /alpha wolf/ can lead to misogynistic non-science content. Even though I don't think anyone should read the links, I supplied them because giving references is how we (should) operate. Cheers, SemanticMantis (talk) 16:10, 13 January 2016 (UTC)