The Darwin fish is an ichthys symbol with "evolved" legs and feet attached and often with the word Darwin inside (like the ΙΧΘΥΣ or Jesus found in some Christian versions). It symbolizes the scientific theory of evolution, for which Charles Darwin laid the foundation, in contrast with Creationism, which is often associated with Christianity. The Darwin fish bears a stylized resemblance to Ichthyostega, which is a major example of a transitional fossil. Related to the Darwin fish is a fish with legs, the word 'evolve', and a hand that is holding a wrench.
Rhetorical scholar Thomas Lessl has conducted a questionnaire survey of users of the Darwin fish emblem. Based on their responses, he interprets the symbol as scientific "blackface," a parody that is one part mockery and one part imitation. While users frequently explain the symbol as a rebuke against Creationism, Lessl suggests that the emblem represents a metaphor for cultural progress.
The Darwin fish has led to competition among bumper stickers. A design was made with a larger "Jesus fish" eating the Darwin fish. Sometimes, the larger fish contains letters that spell the word "Truth." A further step shows two fish, one with legs labelled "I evolved", the other without legs labelled "You didn't". Another variant has a Darwin fish with a mouth, carrying away a smaller, dead Jesus fish by its tail. Yet another variant is the "ixnay" fish (from the Pig Latin for "nix", and punning on ΙΧΘΥΣ). Other variants depict an "Evolution" or "Darwin" fish swallowing an "ΙΧΘΥΣ", "Jesus" or "Truth" fish; another version has a "Science" fish swallowing a "Myth" fish.