Why did life take so long to become multicellular?

[septimus]

This question was asked 14½ years ago in a thread titled “Multicellular evolution – the 2BY gap.”

The conclusion was that oxygen, manufactured by one-celled creatures, was a prerequisite for higher life, and it took a long while to get sufficient oxygen. Dopers seemed satisfied … but 12 years later someone bumped that thread to ask if there were any other ideas. Being a narcissist, I’ll repeat my answer to the bump:

@septimus

One way to guess which parts of evolution were difficult is to consider how often they occurred on Earth.

• Engulfing of organelles to create new kingdoms of eukaryotes? This seems to have happened multiple times.
• Multicellular organisms? My understanding is that multicellular plants, animals, seaweeds, and fungus were all independent developments. (I think I’m missing some kingdoms from that list.)
• The initial creation of replicating chains? There may have been AEG chains even before RNA. AEG chains are still found in some cyanobacteria.
• Ocean life becoming land life? Multiple occurrences.

This is why I think the “invention” of sex was a very key development. It seems to have happened just once. I think it may have been prerequisite to rapid evolution.