With some justification, actually. The jellyfish-like ctenophore is a prime candidate:
The ctenophore was already known for having a relatively advanced nervous system; but these first experiments by Moroz showed that its nerves were constructed from a different set of molecular building blocks – different from any other animal – using ‘a different chemical language’, says Moroz: these animals are ‘aliens of the sea’.
If Moroz is right, then the ctenophore represents an evolutionary experiment of stunning proportions, one that has been running for more than half a billion years. This separate pathway of evolution – a sort of Evolution 2.0 – has invented neurons, muscles and other specialised tissues, independently from the rest of the animal kingdom, using different starting materials.
This animal, the ctenophore, provides clues to how evolution might have gone if not for the advent of vertebrates, mammals and humans, who came to dominate the ecosystems of Earth. It sheds light on a profound debate that has raged for decades: when it comes to the present-day face of life on Earth, how much of it happened by pure accident, and how much was inevitable from the start?
Douglas Fox, “Aliens in our midst” at Aeon
That’s a classic fake controversy. The obvious problem is that—to account for the ctenophore—complex systems had to arise twice, not once, by alleged Darwinian chance. If you doubted chance before, you just doubled your chances of doubting it.
Structuralism might explain it; Darwinism cannot.
As scientists speculate what kind of life might exist on other worlds, a provocative idea is taking hold: that alien life, unlike anything we know, might already exist here on Earth. The idea is that life might have arisen two or more times on our planet – not just once, as long assumed. Our form of life came to dominate, while other forms receded into the corners. This ‘shadow biosphere’ would be difficult to detect, since it might not contain DNA, proteins or the other molecules that we rely on to detect life.
The phylum of ctenophores isn’t quite that exotic. It is based on the same basic chemistry that we share, but it still represents a shadow biology for animals. Ctenophores are a long-lost cousin that we didn’t even know we had.
Douglas Fox, “Aliens in our midst” at Aeon
Well, if there are a lot more shadow biospheres out there, the conventional tale is that much less likely.
See also: If Evolution Were Repeated, Would Jellyfish Be Intelligent?
and
Comb Jellies: Evidence That If Evolution Began Again, Intelligence Would Re-Emerge?
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