科学与数学nautil.us
鸟为什么能飞越珠穆朗玛峰
Why Birds Can Fly over Mount Everest
2020 — 2021，它一次次回到首页
黑点是上首页（≥ 50 分）的那次投稿，空心点是没冲上去的投稿，点越大分数越高。
导读
Nautilus 这篇文章探讨鸟类为何能飞越珠穆朗玛峰，重点介绍鸟类高效的气囊—肺呼吸系统，并延伸到地质历史中的氧气浓度与进化适应。评论补充指出，高海拔低氧下的血液摄氧能力等适应同样关键，而文章对某些历史事件的归因存在争议。
为什么经久不衰：它把生理机制、进化时间尺度和地质变迁串成一个易懂故事，也提醒读者科普叙事中哪些解释可能被简化。
HN 评论精选
文章漏掉血液摄氧适应，气囊系统不能解释低氧下的氧气输送。
文章漏掉了低氧分压以及鸟类在高海拔有效输送氧气的适应。气囊系统适合高需求下的通气，但如果血液根本无法摄取足够氧气，通气率再高也没用，这也是高空需要压力服的原因。恐龙面对 12% 氧气时想必已有特殊血红蛋白等适应，那才是真正原因；高效气囊—肺系统更能解释通气和应对强风。
projektfu查看英文原文
He’s leaving out the bit about the low oxygen tension and what adaptations allow birds to effectively deliver oxygen at altitude. The air sac system is good for high-demand situations, where increased ventilation is needed. But if the blood is simply not able to pick up enough oxygen, the ventilation rate doesn’t matter much. This is why we need pressure suits at high altitude. I’m sure when dinosaurs were dealing with 12% oxygen they had developed adaptations to handle it. Special hemoglobins, etc. Whatever that is, is the real reason. The efficient air sac-lung system is better at explaining how they ventilate well and deal with high winds.
地质渐变给斑头雁逐步适应高海拔的机会。
喜马拉雅山在过去 5000 万年里从无到有缓慢隆起，斑头雁的祖先有机会随着山体升高逐渐适应。并非所有鸟都能做到这一点，即使它们的肺更优越。
wcoenen查看英文原文
It also helps that the Himalayas have slowly grown from nothing over the past 50 million years. The ancestors of the bar-headed goose had the opportunity to gradually adapt as the mountains rose. (Not all birds can do this, even with their superior lungs.) edit: I had assumed that the Himalayas grew gradually over 50 million years, but it turns out that the current growth rate is way too fast for that. It would take less than a million years to reach the current height. There must have been regular apocalyptic landslides in the geological history of the Himalayas to limit the height of the mountains?
鸟肺的单向气流加气囊实现高效呼吸。
简言之，鸟的呼吸系统非常高效：空气从肺的一端进、另一端出，肺内始终有一次完整呼吸，或气囊中有两次呼吸（一次新鲜、一次待排出）。
smegcicle查看英文原文
tldr bird respiratory system is very effective, they breathe in one end of their lungs and out the other, always with either a full breath in their lungs or two breaths in their air sacs (one fresh, one ready to be exhaled) http://www.lslbo.org/wp-content/uploads/2018/10/bird-lungs.jpg
文章对二叠纪末大灭绝的归因有误，主流观点更强调西伯利亚暗色岩喷发。
作者似乎把二叠纪—三叠纪大灭绝归因于微生物获得分解木质素的能力，而多数研究者归因于西伯利亚暗色岩的大规模喷发。木质素分解确实会消耗氧气，但若仅此而已，氧气下降会很慢；实际却在几十万年内从约 30% 降到 12%，说明超级火山喷发等灾难事件可能作用更大。
blacklight查看英文原文
The author seems to pinpoint the cause of the great Permian-Triassic extinction to the acquired ability of microorganisms to process lignin, while most of the researchers attribute it to the extensive Siberian Traps eruptions. Granted, decaying lignin subtracts oxygen from the atmosphere, but had that happened alone the levels of oxygen would have gone down quite slowly. What we see instead is a drop from ~30% to 12% within a few hundreds of thousands of years. It means that a catastrophic event (such as prolonged supervolcanic eruptions) probably played a bigger role.
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