is thumb sucking normal?

it makes me sad when i hear stories of kids who are shamed or have oral thumb-pricking devices implanted, because they suck their thumbs.   it is believed by some that kids suck their thumbs to make up for what they aren't getting at the breast.   according to author and anthropology professor, kathy dettwyler phd, thumb sucking is not seen in babies in nepal, india, ecuador, papua new guinea, mexico, south africa and more.  here is a tidbit from her website:

"My own research suggests that the absolute minimum time human children have evolved to expect breastfeeding to continue is 2.5 years, with a range of 2.5 to 7 years. Thus, one would expect that for many of them, their sucking instincts will remain strong throughout this period, and thus one would expect a child nursed for 2 years to be very likely to still have the instinctive urge to suck til 6, 7, 8 years or even longer. I strongly encourage parents of thumb-suckers to let their children suck their thumbs (fingers, pacifiers) as long as they need to."

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