I think the argument goes both ways. Chimpanzees are (roughly) as intelligent as our toddlers, but we haven't necessarily been treating them as such. That said,

I think the argument goes both ways. Chimpanzees are (roughly) as intelligent as our toddlers, but we haven't necessarily been treating them as such. That said, if we never mentally developed past being toddlers we might not even have invented speech, let alone civilization. Animals possess intelligence well above what people used to give them credit for, whoever they are still far and away from where people are.