Episode 4 of The Story of Life on Earth looks at the ocean long before complex vision existed, when survival came down to an evolutionary arms race between armored, slow-moving animals and faster predators feeling their way through a dark, shifting world.
The episode examines the biological pressures that pushed early marine life toward specialized defenses and offensive strategies, and how that competition laid the groundwork for the more complex ecosystems that came later.
This stretch of the fossil record, often called the Ediacaran and early Cambrian seafloor, is when many of the basic body plans still found in animals today first took shape, worked out through trial and error rather than sight. Hard shells, spines, and burrowing behavior all appear as direct responses to predation pressure, well before eyes complex enough to guide a hunt had evolved. Fossil trackways and burrows from this period are often the clearest evidence of the arms race, showing prey retreating deeper into the sediment as predators got better at finding them on the surface.
That same sweep of prehistory, from the earliest life to the age of dinosaurs, is the subject of Martin’s 2019 book, Life: The First Four Billion Years, illustrated by Grahame Baker-Smith.
Watch Episode 4 on YouTube, start from Episode 1, or see the full series on the YouTube Series page.
Fossil trackways from this period, preserved trails left by armored animals dragging themselves across the seafloor, show sudden changes in direction and speed that many paleontologists read as evidence of predator encounters, physical proof of the arms race playing out in real time.
None of these creatures had anything like a modern eye yet, so most of this arms race was fought by touch, vibration, and chemical sensing rather than sight, which makes the sophistication of the defenses even more striking. Episode 4 argues that this blind, high-stakes competition is what eventually made true vision worth evolving at all.