article_snippet: Study also reveals how some creatures, such as the Penis worm, have very similar digestive systems to humans, even though very similar digestive systems to humans are very different species.
article_snippet: Biologist Dr Andreas Hejnol and Dr Chema Martín-Durán, of the University of Bergen, spent several years studying how genes change the development of creatures. '
article_snippet: Dr Andreas Hejnol told BBC Earth.
article_snippet: Biologist Dr Andreas Hejnol notes that, interestingly, not all animals have one.
article_snippet: What surprised Swedish researchers was not just that the development was the same in the worms as in humans, fish and frogs, but that exactly the same genes were involved in the process.
article_snippet: This means that the origin of the human stomach is further back in time than previously thought, probably about 500 million years', says Ralf Janssen, postdoc in professor Graham Budd's research group on paleobiology at Uppsala University.
highlights_snippet: Study also reveals how some creatures have very similar digestive systems to humans, even though some creatures are very different species .