Simplify the following text for a Grade 9 native English-speaking person.
Original: Burials in barrows or tomb chambers apply to the kurgan culture , in accordance with the original version of the Kurgan hypothesis , but not to the previous Sredny Stog culture nor to the contemporary Corded Ware culture , both of which cultures are also generally associated with PIE .
Simplified: Burials in barrows or tomb chambers ( see Kurgan hypothesis ) .