LUCA: On the Discovery of a Gigantic Lifeform from which All Subsequent Lifeforms Descend

Tree of Life with LUCA at the center (download for magnification)

While I was sleeping off Thanksgiving, the New Scientist wrote this piece about my new fascination: LUCA (the Last Universal Common Ancestor). HT (and then some) Jordan Miller.

What do we know about LUCA?

It existed about 2.9 billion years ago. It was gigantic, filling the planet's oceans. (Haha, we were just talking about Solaris).

It split into three: bacteria, archaea and more complex eukaryotes that gave rise to animals and plants. (In your face underminers! This is a huge entity that split, not smaller objects that assembled!)

5–11% of proteins are common to all lifeforms. Therefore they are in LUCA. These proteins are living fossils of LUCA, which preexist the machinery that now makes them. We have proteins first made by the coding apparatus of LUCA. This is like saying that there are words that preexist all the people who used them. If that isn't spooky I don't know what is. “Language speaks” (Heidegger).

"Structure is known to be conserved when sequences aren't," agrees Anthony Poole of the University of Canterbury in Christchurch, New Zealand, though he cautions that two very similar structures could conceivably have evolved independently after LUCA. (New Scientist)

LUCA had leaky isoprenoid membranes and was multicellular, in order to cope with the rather haphazard way its metabolism worked.  It could digest nitrates and carbon. It probably shared DNA and enzymes between cells (the leakiness was exploited).

All lifeforms have in their cells organelles called acidocalcisomes. LUCA contained acidocalcisomes.

LUCA may not have used DNA. It used RNA instead because RNA can store information and control chemical reactions.

When each individual cell could produce all it needed, LUCA was not required. LUCA became extinct, broke apart into three branches. The ability to process what you need within a bounded container is called death drive. I suggest that the split of LUCA into the three branches of life (see the diagram above) had to do with this increased inner consistency. LUCA died out because beings became more efficient.

What a masterpiece of speculative biology. I'm going to think about this.