A negative result disproves it for the specific kind of memory, e.g. fear of spiders, but you're right that the disproof can't be straightforwardly transferred to claims about other kinds of memories.
The hypothesis is so unlikely given what we know about the brain and reproduction that we'll assume false by default for all memories. Thus the onus is on the experimenter to provide a positive result for some case and also demonstrate that there isn't something else going on.
The hypothesis is so unlikely given what we know about the brain and reproduction that we'll assume false by default for all memories. Thus the onus is on the experimenter to provide a positive result for some case and also demonstrate that there isn't something else going on.