6 International Journal of Pediatrics reﬂex in infants disappears with age, due to the increased inhibition of these upper brain structures. antecedents, do not need to hang on with their hands and feet from the moment of birth. 3.3.3. The Moro Reﬂex and Startle Reaction. Although there has been much confusion regarding the Moro response and the startle reaction in the past, most authors agree today that they are diﬀerent entities [10–12, 17]. The startle reaction, the response to a sudden stimulus, is one of the defensive reactions and consists essentially of ﬂexion movements. It diﬀers considerably from the Moro response primarily characterized by extension. Detailed observations with video recording [90] or ﬁlm [91] and an electrophysiological study with surface electrodes [12] demonstrated the diﬀerences in motor behavior between them. Katona [17] found that the startle reaction induced by an auditory stimulus showed clear habituation in premature infants, whereas the Moro reﬂex did not, and that the startle reaction could not be elicited in anencephalic newborns, while the Moro reﬂex was always elicited in these infants. Pucher et al. [68] investigated the Moro reﬂex using a tilt table with simultaneous monitoring of autonomic parameters including respiration, heart rate, and transcutaneous pO2 and pCO2 and concluded that the reﬂex was not the result of a startle reaction, because of no signiﬁcant alteration in these parameters. 4. Phylogenetic Meaning and Hierarchy of Responses 4.1. Phylogenetic Meaning 4.1.1. The Grasp Reﬂex. In 1891, Robinson [92] described that a newborn human infant was able to support its own weight when it was holding on to a horizontal rod. He tested more than 60 infants under one month old and found that they were able to hang by their hands for at least 10 seconds, and one infant succeeded in hanging for 2 minutes and 35 seconds. Richter [46] had the opportunity of testing the palmar grasp reﬂex in ﬁve monkey infants. They showed a grasp reﬂex that was much stronger than that of human newborn infants. The time of hanging ranged from 7 to 33 minutes with only one hand. Brain and Curran [33] examined the plantar grasp reﬂex in nine adult anthropoid apes and monkeys and found that none of the monkeys showed the grasp reﬂex and that the prehensile function of the adult monkey’s feet was highly specialized, responding to a variety of stimuli. They also observed a number of infant monkeys, some within a few days of birth, slung beneath the mother’s belly or clinging to her ﬂanks only with their hands and feet, receiving no support from her. Although only a day or two old, they held on while she jumped from bough to bough and did not leave her until they were weaned. Based on these ﬁndings, the grasp reﬂex of the hands and feet in human infants could be regarded as a rudiment of phylogenetic functions that were once essential for monkey infants in arboreal life and that have lost their usefulness in the human species [28, 33, 62]. As McGraw [93] stated, modern infants, as well as their fairly recent human 4.1.2. The Moro Reﬂex. In his original paper, Moro [9] emphasized the clasping aspect of the reﬂex and claimed that the reﬂex is a primitive movement analogous to that in young apes and bats, by which they instinctively embrace or cling to their mothers. However, the question has been raised as to his biological interpretation by several authors. Parmelee Jr. [11] stated that Moro’s emphasis in his belief that the reﬂex is an atavistic lifesaving reﬂex resulted in some of the present-day confusion. Mitchell [10] described that in the Moro response, the essential component is the extension movement, and thus it should not be called an “embrace” or “clasp” reﬂex. On the other hand, Amiel-Tison and Grenier [94] commented that the Moro reﬂex can be seen as a hindrance to voluntary motor activity, and this parasitical movement is a nuisance that the newborn retains until a sub- sequent stage of maturation when inhibitory brain function begins. The unique movement behavior of the Moro reﬂex is thus diﬃcult to understand, and its phylogenetic meaning remains unclear. 4.2. Hierarchy of the Reﬂex Responses. Several authors ob- served in human newborns that the palmar grasp reﬂex in- hibits the Moro reﬂex [12, 15, 16, 22, 91]. Later, Katona [17] found in newborn apes and monkeys that the Moro reﬂex was regularly observed and it was inhibited on elicitation of the palmar grasp reﬂex. Because this interrelation between the grasp reﬂex and the Moro reﬂex would be essential for newborn animals to keep clinging and to prevent a fall, the interrelation observed in human newborns could also be regarded as a phylogenetic rudiment. Katona [17] noted another fact that a sudden auditory stimulus triggered a strong reinforcement of the grasp reﬂex in such young animals, which also supports the view that the startle reaction is one of the defensive reactions. Pollack [22] found, in term human newborns, that sucking increased the palmar grasp reﬂex, whereas head rotation had no inﬂuence on this grasp reﬂex. Lippmann noted in human newborns that the Babkin reﬂex consisting of head ﬂexion and mouth opening in response to pressure on the palms of both hands was not obtained during sucking [95]. Brown and Fredrickson [15] also observed in human newborns that the palmar grasp reﬂex did not aﬀect the sucking reﬂex but that the sucking reﬂex increased the strength and the duration of the palmar grasp reﬂex. If the same interrelation between the sucking reﬂex and the palmar grasp reﬂex exists in monkey infants, it would be very helpful for them to ﬁrmly cling to their mother while feeding. The asymmetrical tonic neck reﬂex (ATNR) elicited by head rotation usually induces extension of the upper and lower limbs on the face side in infants. If the palmar grasp reﬂex is predominant over the ATNR in monkey infants, as demonstrated in human infants, head rotation would not bring any reduction in the response of the grasp reﬂex, and the animal infant would keep clinging to its mother. Since the Babkin reﬂex is regarded as the rudiment of hand-mouth coordination for preying in animals [96, 97],