User:Hillgentleman/last universal ancestor

 草文，歡迎大家一齊寫。

• 圖論入面有樣嘢叫lowest common ancestor

最後共同祖先（Last universal ancestor、 LUA；或者叫 LUCA ，last universal common ancestor），係隻假想中嘅生物，係而家地球上全部生存嘅嘢嘅最近嘅共同祖先(en:most recent common ancestor)。估計佢生響36至41億年以前 。

常見誤解

假設無話 LUA 係：

1. 第一隻生物
2. 所有可能中最原始嘅生命

The hypothesis

At the time when LUA was first hypothesized, construction of cladograms based upon genetic distance between all living cells indicated that there was an early split between the archaeans and the remainder of life. This was inferred from the fact that, at that time, all known archaeans were highly resistant to environmental extremes such as high salinity, temperature or acidity, and led some to suggest that LUA evolved in areas like the deep ocean vents, where such extremes prevail today. However, since that time, archaeans have been discovered in less hostile environments and are now believed by many taxonomists to be more closely related to eukaryotes than bacteria, though this is still a matter of some contention.

It is possible that all of LUA's contemporaries would have since become extinct with only the LUA's genetic heritage living on to this day. However, this suggestion ignores the possibility of horizontal gene transfer. Carl Woese has proposed that there was no individual organism which could be considered a LUA, but rather that the genetic heritage of all modern organisms derives from an ancient community of organisms.

See also

• Timeline of evolution
• Most recent common ancestor
• Last Common Ancestor

參攷

[[Category:]] [[Category:]] [[Category:]] [[Category:]] [[Category:]]