A new online game played by more than 1,000 people has revealed why tigers have stripes and how lighting conditions drive the evolution of animal camouflage. The findings could have real implications for wildlife conservation as habitats change.
Why does a tiger have stripes? It sounds like a question from a children’s book, but scientists at the universities of Exeter and Bristol have used a surprisingly fun method to find a rigorous answer: an online video game.
The study, published April 29 in the journal PLOS One, found that high-contrast markings like tiger stripes are most effective as camouflage under direct sunlight and in complex, three-dimensional environments such as tall grass or dense forest undergrowth. Plainer, more uniform patterns, on the other hand, work better in diffuse light — think overcast skies or shaded woodland — and in simpler, flatter habitats like short grass.
How the Game Worked
Researchers designed a game in which players searched for patterned spheres hidden against real photographic backgrounds taken from 28 different UK habitats. The backgrounds were photographed in both direct sunlight and indirect sunlight, capturing the enormous visual difference a sunny day can make.
Over 20 generations of digital evolution, the sphere patterns adapted based on player performance. If a sphere was hard to spot, its pattern was more likely to influence the next generation of designs.
“If a sphere took longer to find, the game used that information to help design the next pattern by combining pairs of the best patterns together,” corresponding author George Hancock, from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall, said in a news release.
The approach essentially mimicked natural selection, with the most effective camouflage patterns surviving and reproducing — all driven by human players clicking on a screen.
What Sunlight Has to Do With It
The key insight is deceptively simple: the world looks dramatically different on a sunny day. Direct sunlight creates strong, directional shadows that add visual complexity to any scene. The more three-dimensional the habitat — say, a forest floor or a patch of tall reeds — the more intense and directional those shadows become.
“When the sun comes out, shadows make the background more visually complex and directional,” Hancock added. “This explains how tigers got their stripes: they match the stripe-like shadows within their environment – and similar patterns evolved within our game.”
The game confirmed what the natural world suggests: animals living in sunny, structurally rich environments tend to develop bolder, higher-contrast markings. Those in shadier or more open terrain lean toward subtler, more uniform coloration. The researchers also observed the evolution of countershading — being paler on the underside, a pattern seen in tigers, antelopes, and even great white sharks — as well as edge disruption, which blurs an animal’s outline against its surroundings.
The researchers also noted that many predators are most active at dawn and dusk, when long shadows ramp up the visual complexity of the environment, potentially making high-contrast camouflage even more advantageous during those critical hunting hours.
Why It Matters Beyond the Animal Kingdom
The implications of this research stretch well beyond explaining tiger stripes. Co-author Jolyon Troscianko of the University of Exeter framed camouflage as a dynamic, ongoing competition.
“Camouflage is essentially a tug-of-war, with both predators and prey investing in various strategies depending on their behaviour and environment,” Troscianko said in the news release.
That tug-of-war is being disrupted. The researchers warn that changes to habitats and lighting conditions — driven by land management practices, urban development, and climate change — could quietly shift the balance for species that depend on specific camouflage strategies to survive. An animal perfectly concealed in its current habitat may become dangerously visible if that habitat changes, even subtly.
“It’s important to understand how such changes might influence animal survival – particularly for species that may already be under threat,” Troscianko added.
Why This Approach Is So Powerful
One of the study’s most notable contributions is methodological. Testing camouflage in the wild is notoriously difficult — you can’t easily run controlled experiments on free-roaming tigers. But human vision overlaps significantly with that of many predatory species, making crowd-sourced online games a surprisingly valid proxy for real predator-prey dynamics.
The use of a genetic algorithm — digital evolution — to generate and refine camouflage patterns across generations adds a layer of scientific rigor that traditional observation alone can’t match. It’s a model that could be applied to a wide range of evolutionary and perceptual questions in the future.
Source: University of Exeter