fossiliferous

Blue-barred Parrotfish

Blue-banded Pitta (Erythropitta arquata), family Pittidae, order Passeriformes, endemic to Borneo

Brooch

c. 1832

Gold, enamel, hair

Longtime Nautilus contributor and the "Indiana Jones of marine biology," Peter Ward has spent decades studying the ancient cephalopod that gave our magazine its name. On an expedition to Australia's Great Barrier Reef, Ward and his colleagues sampled two nautiluses long regarded as separate species. Despite striking differences in their shells and anatomy, DNA analysis revealed no genetic difference between them. The discovery became the starting point for Ward's exploration of epigenetics—the study of how environmental influences can alter the way genes are expressed without changing the underlying DNA sequence. In this essay, Ward argues that epigenetics may help explain why some organisms that appear to be distinct species are actually one and the same—and why Earth may contain fewer species than scientists have traditionally believed.

Atlantic Puffin (Fratercula arctica), family Alcidae, order Charadriiformes, Maine, USA