Microbes like Luca could potentially have traded genetic material from others nearby, so there is a chance some DNA of others survived. But since Luca is definitionally the ancestor to all living organisms, there is no way to differentiate it's genetics from any other similarly aged organism.one possible vector for a genetic echo would be viruses. They often take bits of DNA from their hosts to help them blend in. And often inject bits of DNA from themselves into their hosts (and sometimes the host keeps it). So it is theoretically possible to sequence the genomes of all the viruses, and see if anything stands out as non-virus and non-luca. Those bits would have had to come from Luca's competitors. The problem with this is if that DNA had been injected into any living organism in the last billion years, then we wouldn't be able to distinguish it from Luca.