外網(wǎng)版知乎：如果你和你的異性兄弟姐妹是地球上僅存的人類， 你會為了拯救人類而繁衍后代嗎? 這在道德上是錯誤的嗎?（上）

Ray Friesenhahn
The question of morality here is really not in regards to the violation of the incest taboo, which becomes somewhat irrelevant in the complete absence of any other humans. Consider the perspective of the male, whose sister is now his sole partner for life and survival. Would you put your sole partner at risk (maternal death rate during childbirth was historically around 1%, but would likely be several times that in such conditions, without any experienced helpers) for an outcome that, as so many others have pointed out, has such low potential for success because of the severe genetic bottleneck? Also, from the perspective of survival, your partner would be dependent upon you and unable to contribute much to your mutual survival for several weeks to several months around childbirth, greatly increasing the risk to the survival of all three of you - if the child survives much beyond birth.But consider that the two of you just survived some unprecedented catastrophe - be it man-made, such as nuclear war combined with biological warfare, or natural, such as an asteroid strike or gamma ray burst, followed by disease and climate disruption. You’ve come out of your deep underground bunker after several years surviving on your stockpiles (probably meant to keep a small community alive, but they didn’t make it), and you find you both have immunity to whatever diseases followed the other catastrophes. What you need to keep in mind is that the world is really a very vast place. Even if you wander for years, and use radio transmitters to try to contact others without success, you cannot possibly be certain that you actually ARE the last people on Earth. If you feel an obligation to repopulate the human species on Earth, then it really becomes your duty to continue seeking any other surviving enclaves. With the size and current population of Earth, and great diversity of geographic and environmental conditions, the fact that you two survived means there is a very high probability that some others did as well. Even if you wander for decades in search of them, beyond the time of reproductive viability for yourselves, you will at least have had a mission to give your existence a purpose. Then, if you do finally find others, you could at least help in the rearing of THEIR children, and help to recreate a society, rather than just a species.

這里的道德問題實際上不是關于違反亂倫禁忌的問題，
因為在完全沒有其他人類的情況下，
亂倫禁忌就變得有些無關緊要了。
想想，從男性的視角看，
他的姐妹現(xiàn)在是他唯一的生活和生存伴侶了，
你會讓你的伴侶陷入危險的境地之中嗎？
（從歷史上看，孕婦分娩時，死亡率為1%左右，在題主設置的這種情況下，沒有任何有經(jīng)驗的助產(chǎn)婆，那么
孕婦的死亡率可能還提升好幾倍的）.
正如許多人所指出的那樣，這么高的分娩風險，是因為遺傳瓶頸嚴重吧？
此外，從生存的角度來看，你的伴侶也依賴于你的.
在分娩前后的幾周到幾個月里，你的伴侶也無法為你們的共同生產(chǎn)做出什么貢獻的.
如果你的孩子生下來后，還存活下來的話，那么，你們3個人的生存風險還變得更大.
不過，想一想，你和你的姐妹剛剛經(jīng)歷了前所未有的災難——無論是人為的，比如核戰(zhàn)爭與生物戰(zhàn)的結合;還
是自然的，比如小行星撞擊或伽馬射線爆發(fā)，然后是疾病和氣候驟變，
你已經(jīng)從地下深處的地堡里活著出來了，
幾年來你一直依靠你的儲備食物生存
(那些食物可能是維持一個小社區(qū)生存的食物，但社區(qū)里的人都死光了)，
你會發(fā)現(xiàn)你們對其他災難之后的瘟疫都有免疫力。
你需要記住的是，這個地球真的是一個非常廣闊的地方。
即使你外出亂逛幾年，使用無線電發(fā)射機試圖聯(lián)系他人卻沒有成功，你也不可能確定你實際上就是這個地球
上最后一個人.
如果你覺得有義務讓地球上的人類重新繁衍生息，
那么繼續(xù)尋找任何其他現(xiàn)存的人類，就真的成了你的責任。
鑒于地球的大小和目前的人口數(shù)量，
以及地理和環(huán)境條件的多樣性，你們兩個幸存下來的事實意味著，其他一些人也幸存下來的可能性非常高的.
即使你花了幾十年的時間去尋找它們，
在你自己的生育能力之外，你至少還有一個使命，
那就是給你的存在賦予一個目的。
然后，如果你最終找到了其他人，
你至少可以幫助他們撫養(yǎng)孩子，重建一個社會，
而不僅僅是一個物種。

Patrick Rannou
Well, how could we be sure we’d the last ones? Let’s assume it is the case.In the first few years, we’d be all focused on BASIC survival. Having enough food on the table, so to speak. Starting a family where instead of 2 persons working their ass off just to survive, suddenly only the male now has to provide for 3 persons, that seems quite dangerous until you reach a setup where you are safe and have plenty of stored food and resources to last you a couple bad crops / bad winters years.We’re not medical experts, and me and my sister would be well over 50 years old. by then. So, the risk of miscarriage or of death on childbirth would be wayyyy huge! Sorry but I guess that’s “it” for humankind, then.Even if a new humanity is born, it would eventually be saddled with the weight of several very bad genetic diseases. Not so good a legacy. It’s not as if me or my sister are the best human specimens possible in the first place.I suppose there would be some weak odds of repopulating, but they’d be very low. More like a crazy gamble, really. We’re just a bit too old to have children safely EVEN with all the modern current tech.As for the moral aspects. Well, morality is defined by social convention. With every else “gone”, the only social conventions would be those that we 2 would mutually decide to agree upon. From, today’s point of view, yes we’d both say it’s morally wrong. But as the 2 only survivors? I guess such a traumatic experience could mean that anything becomes possible.Especially after a few years. Don’t underestimate the human need for love and companionship. Feeling alone can be really THOUGH for some people. Oh, at first everything might look and be the same. But a few years down the line, when the only way to survive a harsh winter would be to share a single bed in order to share body heat as much as possible? Yeah, very possible that eventually the brother/sister dynamics get slowly dropped in favor of a “l(fā)ife partners” one. Who knows? Trying to predict how you will change to adapt to a stressful environment, is kind of hard to do.I’d think it would go more along with the survivors state of sex drive and “carefulness”. i.e. take 2 youngsters brother/sister let’s say 10 years old, after a few years they start having high hormones/libido, they each are the only emotional relief in a very dead world, and they are still learning social conventions, making their own path as they go, and liquor stores can hold “good” alcohol for years and years. Contraceptives wouldn’t even be carried, because after a few years, they would be way too out of date. So, 5 years after the weird cataclysm, when they are 15 years old and hormones REALLY kick-in, they get one random night of way too much drinking … and whoops, “things might happen”. Depends on the people.i.e. I’d say it would come more as an accident, after years of loneliness, than on purpose. And not to everybody. If the siblings eventually start having sex, and are of reproductive age, and aren’t super-careful, then yeah, they’d probably eventually have a tons of more-or-less little genetically defective kids, most of whom will die on childbirth or before reaching a few years old.But at my and my sister’s age, the libido might still be there, but lower than before. And we have much more strongly ingrained social virtues and moral compasses. So, yeah, we’d just let humanity “rest” forever.You can’t live without food or air or water, but living without sex is pretty easy.

如何確定我們是地球上最后的兩個人呢？
讓我們假設一下，
在最初的幾年里，我們都專注于基本的生存而努力，
努力保證桌上有足夠的食物.
然后組成一個家庭，以前為了生存，2個人都努力干活，
現(xiàn)在，建立家庭后，突然就變成一個男人干活，提供3個人的生存物資. 這似乎是很危險的.
除非你們兩個先存儲夠用幾年的食物.
而且，我不是醫(yī)學專家，而我和我妹妹都已經(jīng)50多歲了。
到那時。因流產(chǎn)或分娩時死亡的風險將是非常巨大的!
抱歉，但我想這就是人類的生活.
即使一個新的人類誕生了，
它最終也會帶有一些非常嚴重的遺傳疾病.
我和我妹妹并不是最好的人類標本.
我想，我和我妹妹會有一些微弱的重新繁殖的可能性，
但是，這種可能性非常的低.
我和妹妹要生出一個新人類，那就是一場豪賭，真的，
因為我們太老了，就是有現(xiàn)代這么先進的醫(yī)療技術，
我和妹妹也保證不了能安全地生出一個孩子來.
至于道德方面，道德是由社會習俗定義的.
隨著其他一切都“消失”，
唯一的社會慣例將是我們兩人共同決定同意的那些.
從今天的觀點來看，是的，我們都認為兄妹結婚在道德上是錯誤的。
但作為唯一的兩個幸存者呢?
我想這樣的創(chuàng)傷經(jīng)歷意味著一切皆有可能的.
尤其是這個地球只有兩人，相處幾年后，
就算是親兄妹也會合在一起的.不要低估了人類對愛和友誼的需求.
對有些人來說，孤獨的感覺真的很可怕.
哦，一開始一切看起來都是一樣的。
但幾年后，要想熬過嚴冬，唯一的辦法就是合用一張單人床，
兩人盡可能多地分享各自身體的熱量.
是的，很有可能兄弟姐妹之間的關系會慢慢變成“生活伴侶”.
誰知道呢？預測你將如何改變來適應一個有壓力的環(huán)境，是有點困難的.
我覺得，只有兩人的情況下，由性本能來驅(qū)動，應該更符合幸存者的互相“照顧”的行為.
比如兩個10歲的小弟弟/妹妹，
幾年后他們開始有高荷爾蒙/性欲，
他們每個人都是這個死氣沉沉的世界里對方唯一的情感慰藉者，
他們還在學習社會習俗，走自己的路，
而酒類商店也可以經(jīng)年積月地銷售“好”酒.
避孕用品可能都不需要，因為幾年后，它們就會過時的.
所以，在導致人類滅絕只剩兄妹兩人的災難發(fā)生5年之后，
當他們到15歲的時候，荷爾蒙就開始起作用了，
他們會在某個晚上喝很多酒……嗯，啊，哎呀，
“不可描述”就這樣自然發(fā)生了.
也就是說，我想說，在經(jīng)歷了多年的孤獨之后，
“不可描述”的事更像是一場意外，而不是故意的。
并不是對所有人。如果兄弟姐妹們最終開始發(fā)生性關系，
并且到了生育年齡，而且不小心，那么，是的，他們可能最終會有很多或多或少有基因缺陷的孩子，
那些小孩，多數(shù)會在分娩時就死掉，要不然也是活個幾年就死掉.
不過，以我和妹妹的年齡，我們的性欲可能還在，但比以前低了。
我們有更加根深蒂固的社會美德和道德準則。
所以，是的，我們只是讓人類永遠“休息”。
沒有食物，沒有空氣，沒有水，你無法生存，
沒有性生活死不了人的.

Debdoot Das
The incestuous offspring is not the main concern here. First of all, as you mentioned about the high chances of genetic deformities, let us suppose that the offspring produced as a result of in-breeding among the first generation(me and my opposite sex sibling) be without any genetic deformities(highly unlikely). The next(third) generation of offspring would have to be produced either by intercourse between organisms of the first generation and the second generation, or by intercourse between the second generation. These offspring would have extremely high chances of being deformed. The fourth generation would thus have ever higher chances.Thus, in short reproducing with a sibling would do little to save humanity. Every species needs to have a number of organisms greater than its Minimum viable population so that it can survive.
Anthropologist John Moore has declared this number to be about 150 - 180, for providing 60 - 80 generations of humans beings. A study by Rutgers University has stated that 70 human beings have populated Americas, ie, the MVP is 70. In other words, a population of 2(two siblings) can’t reproduce to save humanity. A Population bottleneck is reached quickly if two people start trying to repopulate the world.Also, the scenario mentioned above was an ideal one. In the real world, there are also other factors, like absence of advanced healthcare and doctors(since only two of the siblings are there, and it is unlikely that both of them are super-specialists in all fields of medicine as well as surgery), resource gatherers, etc.The only reason two siblings would engage in sexual intercourse would be for mutual pleasure, because there are not any other people left to socialize with. And they would have to take strict steps for protection, so that no offspring is born. This might be morally wrong, but then again, no one else is there to question morals!

不！我不要亂倫.
主要問題不是說亂倫就沒有后代，而是，首先，正如您提到的，亂倫的遺傳，很有可能是畸形的.
讓我們先假設第一代近親繁殖沒有遺傳畸形(這可能性很低的).
下一代(第三代)則必須通過第一代和第二代生物體之間的交配來繁殖的，或通過第二代之間的交配來繁殖.
這些后代就極有可能產(chǎn)生畸形嬰兒了.
因此，第四代產(chǎn)生的畸形嬰兒就變得比前面的更高了.
因此，簡而言之，兄弟姐妹交配繁殖是不可能繁衍出人類的.
任何物種，想要繁殖下去，都必需要有一定數(shù)量的個體.
人類學家約翰·摩爾說，這一數(shù)量約為150至180個.
這樣交配出來的后代能達到60—80代.
羅格斯大學的一項研究表明，所有美國人是由70個祖先繁衍下來的.
換句話說，2人(兩個兄弟姐妹)的種群是無法繁殖人類的.
兩個人來繁衍的話，人口瓶頸很快就會出現(xiàn).
此外，上面提到的場景是一個理想的場景。
在現(xiàn)實世界中，還有其他因素，
比如缺乏先進的醫(yī)療保健和醫(yī)生(因為只有兄弟姐妹中的兩個人在那里，而且他們不太可能都是所有醫(yī)學和外科領域的超級專家)、資源收集者等等
兄弟姐妹之間發(fā)生性關系的唯一原因是為了共同的快樂，
因為沒有其他人可以和他們交往。
他們必須采取嚴格的保護措施，這樣就不會有后代出生。
這可能在道德上是錯誤的，但話說回來，沒有人會質(zhì)疑道德的!

Randell Nonya
the likelihood of any child being born with a birth defect between you and your sister/brother would be at maximum 7% so if you and your sibling had 100 children only 7 of them would have any birth defect. and while the danger really increases each successive generation of inbreeding it still would never reach 100%. eventually there would be a margin of separation between genetic similarities

兄妹結婚，生出的孩子，最多只有7%的可能會有先天缺陷.
也就是說，你們結婚的生100個孩子，只有7個殘疾.
雖然每一代近親繁殖生出的孩子，殘疾的可能性在增大
但是，可能性并不會達到100%.
基因相似性之間會有一定的界限的.
原創(chuàng)翻譯：龍騰網(wǎng) http://nxnpts.cn 轉(zhuǎn)載請注明出處

Jim Birch
You can be pretty certain that incest has been practised quite often in past and it is probably the reason you are here. Humans have lived in small groups for most our history. Certainly, consanguineous marriage - ie, between cousins - has been completely normal in the past, and still is in a many places. If you grow up in a tribe of a hundred people you are usually all pretty closely related. In larger and more modern societies it provided a way of keeping property in the family.From a gene pool perspective, attempting to recreate a healthy population from two individuals is problematic. This is because the species has a limited set of genes to draw on, to cope with new environmental conditions, diseases, and so on. However, I doubt it is as impossible as some people are suggesting, especially if the initial brother and sister are in good health and have no serious defects. Obviously this means that human genetics take a different and specific path but there is evidence that this sort of genetic bottleneck has happened before. Certainly, the idea that the kids must be weird looking idiots is a myth. They will look like their parents and be about as smart as them. (While "hybrid vigour" is a genuine effect, hybridization also produce a lot of defective individuals.)From an ethical or religious point of view: whatever. Being the only two people on earth is going to produce some serious problems but being forced into a moral tradition to avoid the approbation of others is not one of them. You are it. You have a cultural history but its hold will weaken over time in a very different world. There appears to be a evolutionary trick that acts against close inbreeding. Animals - including humans - generally don't feel attracted to siblings, or more exactly, the kids they were raised with, even if not genetically related.
This effect is observed in various animals, for example, adolescent female chimpanzees will jump troupes, to join unfamiliar males. (This would be too dangerous for a young male chimp, they would literally tear the new guy apart.) It is also observed in the failure of human child marriages to produce offspring. This is probably the origin of the incest taboo: that it produces asexual, childless unxs, not that it produces defective children. If this applies, you simply may not feel like it, even if you are keen to continue the species for philosophical or other reasons. On the other hand, I would not be surprised to find that, after a while, the effect of limited alternate opportunities and radically changed social circumstances does something to whatever moral indoctrination, ideas or feelings you thought you had, and, as they say, the rest is history.

可以肯定的是，在古代，亂倫是經(jīng)常發(fā)生的，
這可能也是你來這里的提問的原因.
在人類歷史上的大部分時間里，人類都是群居的.
這樣，近親婚姻——也就是堂兄弟姐妹之間的婚姻——在過去是完全正常的，就是現(xiàn)在，在許多地方也是存
在這樣的現(xiàn)象的.
如果你在一個有一百人的部落里長大，你們通常都是近親。
在更大、更現(xiàn)代的社會中，近親結婚也是一種保護家族財產(chǎn)的方法.
從基因庫的角度來看，試圖從兩個個體中重建一個健康的群體是有問題的。
這是因為這個物種只有有限的一組基因可以利用，
只有一組基因來來應對新的環(huán)境條件、疾病等等。
然而，我懷疑這并不像有些人說的那樣不可能，
特別是，如果最初的兄弟姐妹身體健康，沒有嚴重的缺陷的話，
我覺得一對兄妹也可以繁衍人類.
顯然，這意味著人類遺傳學走了另一條不同的道.
有證據(jù)表明，這種遺傳瓶頸以前也發(fā)生過.
覺得近親交配生出的孩子一定是長相怪異笨傻，這種想法一定正確.
亂倫的生出的孩子，他們的長相會像他們的父母，和父母一樣聰明.
(雖然“雜交活力”一種基因組合的效果，但雜交也會產(chǎn)生大量的缺陷個體的。)
從倫理或宗教的角度來看:亂倫沒什么大不了的.
作為地球上唯一存在的兩個人，面臨的問題是很多的，
但是，道德問題并不是其中之一.
如果是你的話，那么，一開始，對于亂倫，你是有思想抵觸的.
但是，隨著時間的推移，整個地球只有兩個人的話，
那么，你的抵觸思想會慢慢減弱的.
抵觸亂倫的思想，似乎是一種保護進化的思想，
這種思想可以防止近親繁殖.
動物——包括人類——通常不會被兄弟姐妹所吸引，
或者更確切地說，不會被和他們一起長大的孩子所吸引，
即使他們沒有血緣關系。
這種效應在各種動物身上也能觀察得到的，
例如青春期的雌性動物黑猩猩不會要自己群體里的雄性猩猩，而是要群體外的陌生的雄性.
(這對年輕的雄性黑猩猩來說是很危險了，雌性猩猩所在的群體坑會把新來的家伙撕成碎片).
在早起遠古時代的人類婚姻中，也能觀察到這種現(xiàn)象
這可能是不可以亂倫的（生物）依據(jù):亂倫會生出無性的后代，而不是生出有缺陷的孩子.
如果地球上只剩下你們兄妹二人，即使你出于哲學原因，想要延續(xù)人類這個物種，你也可能不喜歡亂倫.
不過，另一方面，我覺得，你們兄妹二人在那種徹底不同的環(huán)境中相處一段時間后，你們的道德教化、思想或情感會有改變的，正如他們所說的“世事都是歷史，無關道德”.