Wikipedia:Reference desk/Archives/Science/2019 February 12

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February 12

Could it be a biological creature than lay eggs but it soesn't have as sexual reproduction?

Could it be a biological creature than lays eggs but it doesn't have as sexual reproduction? Or in case it has eggs it's necessary to have a sexual reproduction. I'm not sure if in the past I listened to a lecture where the lecturer said that there's a protozoa that has eggs but not sexual reproduction. It was too long ago but I'm trying to understand the principle about the eggs and sexual reproduction anyway. 93.126.116.89 (talk) 12:00, 12 February 2019 (UTC)

Probably not, for the usual definition of "egg". According to the Wikipedia articles, an egg results from fertilization of the female egg cell by the male sperm cells. Mitch Ames (talk) 12:08, 12 February 2019 (UTC)

(edit conflict) Sorry, but wrong. (A RefDesk tip: if you ever find yourself starting an answer with "Probably..." stop and reconsider if you have enough information (or ideally, reference points) to be answering the OP's question in a reliable and useful fashion. I don't meant to be tedious here, but there is currently a WP:VPP discussion in which a number of editors supported closing down the desks, the third such discussion in as many years, with the highest support level to date--and the main gripe of those concerned community members is people throwing out random speculation here, so we need to start enforcing a higher standard to bring this space into alignment with community/policy expectations regarding WP:verification, which is why I am mentioning this openly here rather than on your talk page or Talk:RD. That noted, back to the question).

OP, the answer is yes, it is entirely possible to have an organism reproduce by eggs and still be able to reproduce asexually, and our relevant article is parthenogenesis. There are three main ways in which this can happen:

• Egg-laying species in which the genetics of the egg are typically decided by sexual selection, but in which females (typically when deprived of contact with potential breeding partners for many years) may rarely self-fertilize using a polar body. This happens rarely with many species of reptile, but even with those species where it is known, it is a rare occurrence under extreme conditions and the offspring are often unhealthy, as they are, for all genetic purposes, prone to the same conditions inbred animals are. The offspring resulting from such occurrences are often called "half-clones".
• Some egg-laying species (typically but not exclusively eusocial insects like ants, bees, and wasps) have sexually dimorphic dynamics in their life cycle mechanics by which a majority of their offspring are produced asexually. For example, the queen of a eusocial species usually lays the majority of her eggs without their being fertilized. These offspring then typically grow into drones, the male breeding stock, whereas the eggs which are fertilized become either 1) female "workers" who do most of the labour of the colony and are called "sister clones" of one-another, but are infertile or 2) new queens capable of reproduction (in some species, there is one class of female offspring who begin their lives as workers, but later in life a certain percentage will morph into queens under the right conditions (usually when the season for nuptial flights is approaching and the colony is read to expand or send out new founding queens to create their own colonies).
• Finally, there are egg layers that rely on obligate parthenogenesis, meaning their entire species reproduces in this fashion. There are a fair number of species from all over the eukaryotic branch of the tree of life that do this, from relatively simply creatures like rotifers to much more complex creatures--with reptiles once again representing a large chunk of such species (a well-known example being the all-female whiptail lizard). However, it's worth noting that outside of a small handful of cases, it is typically believed that most such non-microscopic species that rely on obligate parthenogenesis in their egg-laying lifecycle originally evolved from an earlier form in which the progenitor species was sexual in nature; a female at some point in the genetic lineage was born with a propensity to self-fertilize (see group one, above) and because of the ecological niche for that species, and genetics that allowed it to avoid the worst of the drawbacks of such asexual reproduction, she and her offspring became the passthrough for a successful successor species. Even so, some such species are thought to be self-terminating as they will slowly accumulate conditions which would be bred out in their sexual progenitors and close living relatives who remain sexual. It's just that they may still be successful enough to stick around for a long while as this process takes its toll.

Additionally, there are other asexual egg-laying organisms which are not partehnogenetic, but most single-sex species will fall into that class. I highly recommend the first article linked above, as I have only touched upon the diversity of such species and the nature of their genetics and lifecycles in the broad strokes above, whereas the diversity of mixed sexual and asexual species is actually well beyond my ability to summarize here. Snow ^{let's rap} 13:10, 12 February 2019 (UTC)

... stop and reconsider if you have enough information (or ideally, reference points) to be answering the OP's question in a reliable and useful fashion. ... WP:VPP discussion ... people throwing out random speculation – I quoted or paraphrased, and linked to, Wikipedia articles that explicitly define "egg" etc; that's hardly "random speculation". The discrepancy between your answer and mine is in the definition of "egg", hence my "usual definition of ...". The term evidently has different meanings in different contexts. (It's interesting that Egg's lead section doesn't explicitly mention that the word is also commonly used for unfertilised egg cells, eg chicken eggs; that usage is only mentioned indirectly via the hatnote to Egg as food).

Incorrect again, I am afraid. It doesn't matter which definition of "egg" you were using (female gametes in general or specifically eggs which hatch outside the female's body in a non-viviparity fashion), because both are utilized by at least some species that propagate via asexual reproduction. Therefore the reason your response was incorrect was not by any means just because you opted for one meaning over the other...as you would have noted if you had read the remainder of my response to the OP after the portion that offended you (and again, that comment was not intended for the purpose of offending you but rather because we need to get serious about only having well referenced and factual responses rather than speculation. I'm sorry to be so blunt about it: yours is certainly not the biggest mistake ever made on the desks when venturing a guess, but after three VPP discussions to close the desks in successive years, I feel those of us who want to argue that this place can exist within policy constraints need to start promoting approaches that prove that assertion.) Snow ^{let's rap} 13:51, 12 February 2019 (UTC)

Could you explain exactly which part of my reasoning was incorrect? Using the definition of egg (not egg cell) in that article, and subsequent definitions for other linked articles (with my italic emphasis added):

• The egg is the organic vessel containing the zygote ... An egg results from fertilization of an egg cell.
• A zygote is a eukaryotic cell formed by a fertilization event between two gametes.
• Fertilisation ... is the fusion of gametes ... This ... is called sexual reproduction
• A gamete is a haploid cell that fuses with another haploid cell during fertilization (conception) in organisms that sexually reproduce.

Alternatively, are the articles quoted above incorrect, or missing something (eg "an egg can also be the result of [something that is not sexual reproduction])? Mitch Ames (talk) 03:52, 13 February 2019 (UTC)

The point is this: the OP asked a question that was perfectly straightforward, even with the broken grammar: "Are there any egg-laying species that can reproduce asexually?" Your answer was "Probably not, because..." which was both speculative and quite simply factually incorrect. Now, it doesn't matter what definition you were using for "egg" or how reasonable your conclusions were in light of that choice, because we are not here to "reason out" any "probable" answers to the question: if you are tempted to provide what seems like the likely answer from synthesizing disparate facts together, please don't--this is no more the space for that than is any article or talk space on Wikipedia. If you can answer a question with a series of references and a summary of said references which directly answer that inquiry without speculation, go for it. If, however, one cannot answer a question directly without some guesswork and personal attempts to fill in the blanks of knowledge with extended personal reasoning, that person should not be answering that particular question. (And of course, sometimes there are questions that no user can answer without speculation, but that's just the limitation of this space and it's function within the project).

But just to respond to your inquiry quickly since it now includes particular factual requests that you presumably want an actual answer to: 1) yes, an "egg" can be an "organic vessel containing the zygote...result[ing] from fertilization of an egg cell." However, fertilization can occur in some species which lay such eggs, without the benefit of sexual reproduction. 2) It's generally true that a "zygote is a eukaryotic cell formed by a fertilization event between two gametes." However, other types of haploid cells are capable of fertilizing an ovum; it is not always a fusion of gametes from a female and male donor. 3) "Fertilisation ... is the fusion of gametes ... This ... is called sexual reproduction"; this is the crux of where I think your confusion arises (I don't really have time to go back and re-analyze the actual grammar involved from the original sentence you pulled into chunks here such as to qualify whether it became incorrect as a result of the manner in which you quote it or it was inaccurate to begin with, except to say that as you quote it here, it is not a correct statement): "fertilization" is not synonymous with "sexual reproduction"; it is one process in the phenomena of sexual reproduction. It is absolutely a necessary part of that phenomena, but it is not exclusive to reproduction in sexual species; fertilization also takes place in asexual species--including some that "lay eggs"--and in that context the ovum is "self-fertilized" by some form of haploid cell other than a male gamete. I believe the explanation of the fourth quote is subsumed within the answers to the first three, so I won't belabour the point. Snow ^{let's rap} 19:58, 13 February 2019 (UTC)

"Fertilisation ... is the fusion of gametes ... This ... is called sexual reproduction" ... is not a correct statement. – OK thanks for that. I've raised the issue at Talk:Fertilisation#Is fertilisation incorrectly defined as "sexual reproduction"?. Perhaps you could follow up on the matter there, and fix or clarify that article if necessary.

(Note that one of the purposes of the reference desk is to "help the growth and refinement of Wikipedia by identifying areas that may need improvement. If an article that could answer a question is lacking the relevant information [fertilization of an egg can occur asexually], look for a way to work the information into the article. This provides a lasting value to the project.")

Mitch Ames (talk) 02:51, 14 February 2019 (UTC)

(edit conflict) There are not "eggs" in any meaningful sense during asexual reproduction, because by definition, an egg is the gamete of the female sex of a species. Without females (and by contrast males) the concept of an egg really could only be applied to asexual reproduction by metaphor or analogy, not as a real "egg". There are processes like Budding and and some kinds of Spores which could, I guess, maybe, be kinda thought of like eggs. Maybe? --Jayron32 12:12, 12 February 2019 (UTC)

The meaning of "egg" is a little ambiguous as it gets used by laypeople to refer to both fertilized eggs and unfertilized egg cells in animals. Hens lay "eggs" without benefit of a rooster. However, these are technically egg cells. It's the same concept of how a human female lays "eggs" every 28 days (don't call it that); those are, again, only egg cells unless/until they get fertilized. Matt Deres (talk) 12:56, 12 February 2019 (UTC)

Still, the two definitions of egg are 1) the unfertilized gamete produced by a female or 2) the gamete of the female after it has been fertilized by the gamete of the male. Either way, those are close enough to each other that they both require the concept of "female" which requires the concept of "sexual reproduction". Without sexes, you don't have eggs. You have something else. --Jayron32 13:00, 12 February 2019 (UTC)

It's actually not nearly that simple (see my response above). While "egg" is often treated as a synonym for ovum, most working in the biological sciences will use the former only when discussing non-live birth breeding, to avoid that confusion, though admittedly, whenever discussing such terms when there is no chance for confusion (such as with humans) there is a marked propensity to relax that rule and default to simply "egg", especially when talking to a lay person who may not recognize what "ovum" means.

Anyway, more to the point, the statement "Without sexes, you don't have eggs. You have something else." is absolutely false. See our article on parthenogensis for an introduction to the many, many species that produce eggs without the benefit of two sexes (sometimes for sexually dimorphic reasons, sometimes as the standard for producing all offspring). Snow ^{let's rap} 13:18, 12 February 2019 (UTC)

Good point! --Jayron32 13:52, 12 February 2019 (UTC)

You beat me to it. But also, "egg" has a third meaning which is much more common, which is not a cell but an object. A chicken egg, after all, is not just a yolk but also vitelline membrane, albumen, shell membranes and shell. In practical terms anything that can be laid and grow up into an organism is likely to be called an egg by this practical definition, whether it can conceptually be fertilized or not, i.e. whether it contains an oocyte and/or zygote or not. Wnt (talk) 14:47, 12 February 2019 (UTC)

Many worlds interpretation

In the wikipedia article it cites Davies and Brown, as well as Simon, that if two branches merge to become branch, then all memories of the previous split will disappear? Why do they insist on this?Rich (talk) 23:02, 12 February 2019 (UTC)

As the name already hints out, its an "interpretation". Most details are only determined to be logical aka cause no contradictions. That puts such theories close to Self-fulfilling prophecy a priori because of the "i want a theory"-approach aka the self constructed Illusion of validity. --Kharon (talk) 23:51, 12 February 2019 (UTC)

Sometimes the line between science and science fiction is rather narrow. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:26, 13 February 2019 (UTC)

Quantum mechanics is time reversible. To talk out my ass a little, if our universe were to split, in the future, into two or more "many worlds", then we can't tell which one "we" are going to go to, because we go to both. When you point a new super powerful telescope at a section of space no one has "observed" before, conceivably you might collapse not only the photon wavefunction but the actual location and nature of the star at the moment you first do a measurement. Before there was just a smear; now there's a single physical object, or to interpret it differently, a lot of universes with vastly different planets and alien empires on that distant bit of real estate have just been split up. Similarly, one universe might have more than one past, the same way. I mean, if there's one world where Hapshemseput was the father of Tukhanakhman and another where it was the other way around, and everyone forgets which was which (and, more implausibly, all conceivable physical evidence is effaced) then the two become the same world. Maybe, though that may seem a bit ridiculous. It is relatively hard to see situations where entropy decreases, yet here and there it does so long as it increases on average. I'll leave this as an idea for discussion rather than representing it as a factual answer; I've come to disbelieve many-worlds anyway. Wnt (talk) 01:07, 13 February 2019 (UTC)

maybe you believe mwi in other universes.Rich (talk) 02:24, 13 February 2019 (UTC)

Wnt, one should be careful here. The classical Copenhagen interpretation is not time reversible because the concept of wave function collapse is not a reversible process. Mostly since the 1970s/80s, physicists have developed a theory of quantum decoherence that seeks to replace the concept of wave function collapse in quantum mechanics. Decoherence argues that what we generally perceive as wave function collapse is really only an approximation of the true evolution of the system. With decoherence replacing the original wave function collapse, quantum mechanics is time reversible; however, I'm not sure there is an agreement that decoherence is really the right understanding of the underlying measurement process. The many-worlds interpretation was in some ways inspired by the development of the theory of decoherence. Dragons flight (talk) 16:07, 13 February 2019 (UTC)

• Interpretations like Copenhagen and Many-Worlds and the like are not really scientific concepts, because they are not necessarily falsifiable concepts. You can't run an experiment or gather data or make observations to establish which of the competing interpretations is wrong, as such, since you can't falsify it, it's not really in the realm of science. Many physicists are critical of any attempt to introduce woo into an otherwise sound scientific discipline like QM, and see all of these explanations as just so much "take-it-on-faith-because-if-you-think-about-it-this-way-it-makes-more-sense" explanations. Physicist N. David Mermin summed it up well, with his exhortation to "Shut up and calculate" whenever these discussions start up. --Jayron32 15:13, 13 February 2019 (UTC)

The cited article explains that merging of two branches would require "all "memory" of the earlier branching event to be lost, so no observer ever sees two branches of reality." Each observer perceives only a rational history that has credibly led to the post-merge reality on which everyone agrees, and two pre-merge observers simply become a single post-merge observer. The many-worlds interpretation does not actually allow memory of a split to arise, though one might speculate unfruitfully that a living cat is dead or a dead cat is alive. DroneB (talk) 15:22, 13 February 2019 (UTC)

• This plays an important role in a though experiment proposed by David Deutsch to experimentally falsify the Copenhagen Interpretation (CI). This involves an observer implemented in a quantum computer ( Deutsch invented his thought experiment before quantum computers were proposed, he invoked a device with similar properties). The virtual observer can then perform a virtual quantum measurement, the act of making the measurement can then be partially reversed such that the measurement outcome is erased, but the information that the measurement was indeed performed is not lost. One can show that this partial reversal can be implemented using only unitary transforms, and since any arbitrary unitary transform can be implemented by quantum computers, it follows that such a virtual observer can falsify the CI by verifying that after the reversal, the system is in the same state as it was before the measurement was made. CI predicts that due to the collapse of the state after the measurement is made, the reversal operation won't restore the initial state of the system. Count Iblis (talk) 19:15, 13 February 2019 (UTC)

Wnt's statement that entropy "increases on average" can be misunderstood if no link is made to his/her earlier statement that "Quantum mechanics is time reversible". See "Arrow of time" (February 9, above).2A00:23C4:7939:B000:D948:5178:7C4A:A389 (talk) 09:35, 14 February 2019 (UTC)

"the information that the measurement was indeed performed is not lost" That's the key to fixing the apparent paradox you introduce. 1) Observers must always be part of the system they observe. You can't observe a system with which you are not physically interacting with (i.e. you either have to receive a particle from that system, or you have to emit a particle which interacts with that system) which means you are now part of the system. The concept of the isolated system which the observer is not part of does not exist. This is called the Observer effect. 2) Now that the observer is part of the system, we can see how we still cannot get back to the initial state without destroying the information. If we go back to the initial state including the initial state of the observer where the information about the change is stored, then we have undergone an actual time reversal. However, insofar as the observer has stored information about the event (i.e. has memory of the event) then there is a physical difference in the system between the before and the after. You thus have the problem that if the observer returns the system to its initial state, that includes erasing its own memory so that it has no way to compare the second to the first. Either A) You can't return the system to its initial state or B) You can, but you can't provide any evidence that you did, and have no memory of having done so. We have a word for things that we say happened, but have no evidence for, and it's not science. --Jayron32 13:43, 14 February 2019 (UTC)

So, Jayron, are you a Copenhagenist?Rich (talk) 08:26, 16 February 2019 (UTC)

I'm a shut-up-and-calculatist. Aka, an instrumentalist. --Jayron32 13:26, 18 February 2019 (UTC)