Cavers found a new human relative deep inside an almost inaccessible South African cave

In 2013, recreational cavers squeezed through a chute barely 18cm wide and found a chamber scattered with hundreds of fossil bones belonging to an unknown hominin. Named Homo naledi, it had a brain about a third the size of ours, yet the bones' position has led some researchers to argue, controversially, that a small-brained species was deliberately placing its dead there.

— Lee R. Berger et al., Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa — eLife, 2015