'd' and 'p' are close enough. specially since the point of contrast is the 'm' of the opposite(complimentary) concept/sound/principle: ma ma
consider all the sounds humans can produce
now ask yourself
1) amongst them, if p and d are close (there is no world in which the answer to that is "no")
2) if there are real life examples of languages shifting between them or using them interchangeably (there are, papa and dada being a prime example)