Piles of faeces left by rock hyraxes may be clues to our past Natalia Kuzmina/Alamy
Middens are fossilised piles made of faeces that have shown that Yemen's desert valley was once a tropical oasis. This may have been possible because of human land management practices.
Wadi Sana today is a dry and rocky desert. We know that the Arabian peninsula was wetter 11,000 to 5000 years ago than it is now. Some lake-bed deposits suggest that grasslands or trees could have been grown elsewhere in the interior.
