generations

"This approach to learning contributes to what we call 'cumulative culture' -- the ability to build on existing knowledge and pass it down through generations," Hewlett said.

The population of the white-backed vulture, for example, declined by around 90 percent in just three generations -- equivalent to an average decline of 4 percent per year.

However, pedigrees are recorded manually, and they may go back only a few generations.

For generations of Palestinians, it is their link to the land - a link that is under threat now more than ever.

Along Colombia's Pacific coast, a small shellfish called piangua has been a crucial part of local communities for generations.