Reading 5 Flashcards
What have researchers argued about the uniqueness of human birth? Why has this not been substantiated?
Researchers have argued that the process of human birth is unique among primates and mammals in that the infant emerges with its face oriented in the opposite direction from its mother (occiput anterior) and head rotation occurs in the birth canal.
However, this notion of human uniqueness has not been substantiated, because there are few comparative studies of birth in non-human pri- mates.
What does this paper report?
This paper reports the mechanism of birth in chimpanzees (Pan troglodytes) based on the first clear, close-up video recordings of three chim- panzee births in captivity. In all three cases, the foetus emerged with an occiput anterior orien- tation, and the head and body rotated after the head had emerged. Therefore, these characteristics are not uniquely human. Furthermore, in two of the three cases, the chimpanzee newborns landed on the ground without being guided from the birth canal by the mother. The fact that the human new- born emerges with an occiput anterior orientation has thus far been taken as evidence for the necessity of midwifery in modern humans, but this view also needs revision. Our observations raise the need to reconsider the evolutionary scenario of human birth
What are the three aspects researchers have argued make the process of human birth is unique among primates and mammals?
Researchers have argued that the process of human birth is unique among primates and mammals in three aspects: the mechanism of birth, difficulty of labour, and behaviour during and after labour [3–5].
What does the mechanism of birth refer to? Has this been considered a simple or complex process traditionally? What has been the traditional explain for why the mechanism of non-human birth is a simple process?
The mechanism of birth refers to the way the baby adapts itself to and passes through the maternal pelvis [6].
Traditionally, the mechanism of birth in non-human primates has been considered a simple process (e.g. [3,5,7]).
The foetus passes through the birth canal without significant changes in orientation, although one report indicated the rotation of monkey foetuses through the birth canal of a different sort from that seen in humans [8].
The head of the foetus emerged from the birth canal with its face oriented towards the anterior side of the mother (occiput pos- terior, figure 1a). This occiput posterior position is adaptive because the mother is able to safely lift the infant towards her and clear its breath passage soon after the birth.
Why do people think the mechanism of birth in modern gumans involves a number of movements and rotations of the head of the foetus in the birth canal? How does the human fetus usually emerge from the birth canal? Is this considered to be advantageous? What have people believed about this unique aspect of human birth?
In contrast, the mechanism of birth in modern humans involves a number of movements and rotations of the head of the foetus in the birth canal (e.g. [3– 5,7]). This is due to the tortuous birth canal and close correspondence of the size of the foetal head with the size of the birth canal in humans, which leads to difficult parturition, the second unique human aspect of birth.
Usually, the human foetus emerges from the birth canal ‘facing away’ from the mother, with its face oriented towards the backside of the mother (occiput anterior, figure 1b). This is considered to be disadvanta- geous because the mother cannot meet the immediate needs of the infant after the head emerges [4]. It has been suggested that the occiput anterior emergence pat- tern accounts for the third uniquely human aspect of birth, that is, the birth is attended by other individuals, such as midwives, and mothers actively seek assistance in childbirth [4,5,7,9].
is the notion about human uniqueness confirmed? Why or why not?
However, the above notion about human unique- ness is not entirely confirmed because there are few comparative data on birth in non-human primates [10].
Birth in non-human primates is generally a soli- tary event, and observers have had few chances to record births in the wild. In addition, the process of parturition is quick, and precise prediction of its timing is difficult. Thus, it is extremely rare that obser- vers are able to witness the event in close enough proximity to determine the mechanism of birth in cap- tive settings. Here, we report the orientation of chimpanzee newborns when they emerge from the maternal birth canal based on the first clear video recordings of the births of chimpanzees.
LOOK at Figure 1. Schematic drawings of the emergence of newborn. (a) Occiput posterior orientation in monkeys. (b) Occiput anterior orientation in humans.
Look at
Figure 2. Schematic drawings of the orientation of the face and shoulders when the newborn chimpanzees emerged from the maternal birth canal. The drawings are based on the video recordings. Case 1: Tsubaki was the mother and Natsuki was the newborn. Case 2: Misaki was the mother and Hatsuka was the newborn. Case 3: Mizuki was the mother and Iroha was the newborn. (a) Emergence of the face and (b) the shoulders.
In the three cases of the study, in what position did the fetus emerge? What happened after the fetus was born in case 2? case 1? case 3?
In each of the three cases, the foetus emerged in an occiput anterior position (figure 2; electronic supplementary material, videos S1 – S3).
After the entire body emerged, the newborn was immediately lifted up by the mother in case 2, and it dropped onto a straw layer on the floor in cases 1 and 3.
What was case 1?
Case 1: Tsubaki was the mother and Natsuki was the newborn.
what was case 2?
Case 2: Misaki was the mother and Hatsuka was the newborn.
What was case 3?
Case 3: Mizuki was the mother and Iroha was the newborn.
what does (a) show?
an emergence of the face
What does (b) show?
an emergence of the shoulders
What do these observations contradict? What were observation in the early 20th century based on? Can these current findings be generalized? Why or why not? What is most plausible to assume?
Our observations contradict the traditional view that the occiput anterior position and head rotation are unique to human birth.
Observations in the early twentieth cen- tury, which were based on direct observation without videos, have indicated the presence of the occiput anterior position in captive chimpanzees [12], but recent discussions have rarely referred to this obser- vation. We cannot generalize from just three cases, which may involve idiosyncratic exceptions to general rules, but it is more plausible to assume that the pattern we observed is a result of regulating factors, because the three cases were similar in terms of the direction of the face and shoulders when they emerged.
