‘The first time it happened, it gave rise to all complex life,’ scientists say
It’s certainly possible that it is happening constantly, and we’ve only started looking for it recently. I’ve had a tinker with writing a better headline and it’s not easy. What would your short, pithy, accurate and unambiguous headline be - suitable for a non-technical audience?
“New bacteria/plant cell symbiosis discovered”
And if “symbiosis” is too much, “combination”. I also like “meld(ing)”, but that might be somewhere in the middle.
I wouldn’t use “hybrid” because that word has definitely made it into common vernacular and implies they’ve bred which isn’t strictly accurate, and “chimera”, while more accurate, is probably the more terrifying-sounding, if not still technical alternative.
“First evidence in a billion years of two lifeforms merging into one”
It’s slightly shorter and more accurate… it does not state absolutely that it happened for the first time, but rather that it’s the first evidence we’ve found from the last billion years.