How so? If great filters exist at all, which is not a given, there could be multiple ones, first of all. They could be somewhere between our level of biologica

How so? If great filters exist at all, which is not a given, there could be multiple ones, first of all. They could be somewhere between our level of biological complexity and the kind hypothesised to be responsible for this signal. Endosymbiosis is a very plausible such filter. The evolution of language and the bootstrapping of cultural evolution is another one. Both n=1 on our planet. Probably there are others I can't think of right now.