The Evolution of the Stomach
The Missing Link
Future research can look for a missing link in the evolution of stomachless animals. Animals lacking a stomach but having an acidic part of their digestive tract could represent an intermediate stage in the evolution of the stomach.
Stomach Variations in Different Animals
Horses, rabbits, and hamsters only have one stomach. Camels and dolphins, on the other hand, have three stomachs. The platypus is unique in that it has no stomach.
The Origin of the Stomach
The stomach, defined as an acid-producing part of the gut, first evolved around 450 million years ago. This allowed animals to break down food more efficiently.
Multiple Evolutionary Attempts
Stomachs evolved some 450 million years ago, but after giving this organ a test drive on 18 separate occasions, ancestors of contemporary stomachless animals abandoned it.
Characteristics of Stomachless Animals
No stomach-free animal had genes to produce an acid-rich zone in its digestive tract. Animals without stomachs also lacked genes or had inactive genes for producing certain digestive enzymes.
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