"If 'Lucy' wasn't alone, who else was in her neighborhood? Key fossil discoveries over the last few decades in Africa indicate that multiple early human ancestor species lived at the same time more than 3 million years ago. A new review of fossil evidence from the last few decades examines four identified hominin species that co-existed between 3.8 and 3.3 million years ago during the middle Pliocene. A team of scientists compiled an overview that outlines a diverse evolutionary past and raises new questions about how ancient species shared the landscape."
Not that I ever thought this was implausible but 'evidence' never hurt a theory. As I find with many processes, I find them to very simply make sense. Our remaining minute bits of Neanderthal in our DNA is another tidbit of that evidence.