[perl4ever]

"Eukaryotes are basically a fluke. The symbiosis event that created Eukaryotes from a random combination of Archaea and Bacteria appears to have happened only _once_ in the entire history of the earth."

Isn't it possible that once it happened, it filled a niche that prevented something similar from happening again? Thus, the fact it only happened once doesn't tell you how probable it was to happen at all.

I have the impression other similar things may have happened as well. Recent articles about a viral-like protein that may be crucial to how long term memory works suggest that chance combinations of life that melded may be a theme.

[bduerst]

>Isn't it possible that once it happened, it filled a niche that prevented something similar from happening again?

Except it did happen again. Chloroplasts and mitochondria organelles are so different they are considered to have been generated from separate events.

Assuming that there are niches though is dangerous, because it assumes the evolution is guided, which it isn't. It's entirely possible that this has happened many times throughout history, but the resulting new organisms couldn't compete and died off without a leaving a trace.

That's why assuming it only happened twice is survivor bias.

[perl4ever]

"Assuming that there are niches though is dangerous, because it assumes the evolution is guided, which it isn't"

No, I wasn't suggesting that evolution is guided. If something evolves, and it ends up in the way of anything evolving similarly, it's not purposeful. It just is, as long as some catastrophe doesn't clear the way.

Edit: your comment "It's entirely possible that this has happened many times throughout history, but the resulting new organisms couldn't compete and died off without a leaving a trace." is a distinction without a difference to me. That's what I meant by it not happening, and the existing organisms occupying a niche.