The observations that supported their conclusions include; Bird wing butterflies were found throughout the Malay archipelago, but species differed slightly from island to island.
Bird families clustered geographically: cockatoos in the Malay Archipelago and Australia, macaws and hummingbirds in the America.
Mockingbirds from different Galapagos islands had Subtle, consistent differences.Tortoise from different Galapagos islands have distinct shells
The bony shells of armadillos resembled fossilized shells from the extinct Glyptodon.
The fossilized remains of giant sloths were similar to the smaller, living sloths Darwin encountered. Therefore, the resemblance between species and the variations among distant species led to both Darwin and Wallace to conclude that species change over time.