Simplify the following text for a Grade 7 native English-speaking person.
Original: This has led the discoverers of H. floresiensis to conclude that the species , or its ancestors , could only have reached the isolated island by water transport , perhaps arriving in bamboo rafts around 100,000 years ago ( or , if they are H. erectus , then about 1 million years ago ) .
Simplified: Because of this , the discoverers of H. floresiensis think that the species , or its ancestors , must have reached the isolated island by water transport around 100,000 years ago ( or , if they are H. erectus , then about 1 million years ago ) .