There are logical flaws in the current explanations of fixated thumb and dummy sucking.
1. The need to suck: This does not explain why infants fixate on one sucking object, say one digit out of 10 when thumb-sucking.
2. Hunger: There is no nutrition in thumbs and dummies; thumb-sucking will also occur after feeds.
3. It is normal behaviour: In societies where the babies are carried close to the bare breast then fixated thumb-sucking is rarely observed. Other mammals also fixatedly thumb or body part suck, such as fixated penis sucking in monkeys when they are human reared.
4. It does no harm: Just as a monkey will suck the penis to the point of it becoming gangrenous, so human infants suck their thumbs to the point of excoriation and to the point of developing facial malocclusions.
5. It occurs as part of learning: One-teat preference, also known as teat fidelity, teat selection, teat territoriality, teat preference and nipple confusion is present across the mammalian spectrum, both altricial, premature and precocious.
It is important to differentiate between (1) bonding (adult type behaviour), (2) attachment (which occurs in infancy from about 6 months of age when the whole mother is recognised and differentiated from the environment), and (3) imprinting (which in the mammal is oral, occurs quickly after birth, and is on part of the mother or, as in thumb and dummy sucking, on a decoy). Oral mammalian imprinting can be considered a vestigial remnant and an evolutionary survival strategy.