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Flashcards in Case 1- Birth Deck (81):
1

Evolutionary Pathways to Disease and/or Health

• An evolutionary matched environment.
• An evolutionary mismatched or novel environment.
• Outcomes of demographic history.
• Outcomes of cultural history. • Outcome of evolutionary constraints.
• Sexual selection and “sexual”competition and their
consequences.
• Life-history and/or developmental associated factors.
• Antagonistic pleiotropy.
• A harmful allele when homozygous is maintained by heterozygote
advantage.
• Effects of deleterious allele does not become apparent until after reproductive age.
• Spontaneous mutations for a deleterious gene defect replace alleles eliminated by selection.
• Exaptation.
• Excessive and uncontrolled defense mechanisms.
• Fighting the evolutionary arms race with microbes.

2

Three relevant histories in systematic evolutionary framework

• #1: History of the complaint. • #2: Developmental history of the person.
• #3: Evolutionary history of the person and
their ancestors.

3

Unique qualities of humans
compared to apes

• Upright posture and bipedal locomotion.
• Unique pelvic dimensions with relatively narrow pelvic inlet & outlet.
• Disproportionately large brain/body size compared to other primates.
• Less mature neurologically at birth than other primates.
• Greater proportion of brain development occurs after birth compared to other primates.

4

Hominid timescale
IMPORTANT

• Paleolithic age (stone age): 2.5 million years ago to 10,000 years ago.
• Neolithic age (late stone age with emergence of plant and animal domestication): 10,000 - 4,000 years ago.
• Bronze age (metal tools widely used): 5,300 - 2,400 years ago.
• Iron age: 3,300 - 1,600 years ago.
• Silicon age: 1971 - present

5

Childbirth problems in Paleolithic and Neolithic populations

• Some paleo-archeological studies have estimated that during the Paleolithic times there was a 15% chance of maternal death in pregnancy or childbirth.
• In pre-Columbian Amer-Indian populations in Neolithic times the estimated age of death correlates with pelvic inlet size, suggesting that complications of pregnancy were a leading cause of death in reproductive age females.

6

Relative mismatch between newborn head size & maternal pelvic outlet size

• Today, in a significant percentage (2%) of pregnant Homo sapiens women, there is a mismatch between fetal/newborn head size and maternal pelvic outlet size
resulting in need for cesarean section (when available) or maternal/fetal death when surgical cesarean section is not available.

7

Relatively high rates of labor and delivery difficulties in Homo sapiens

• In many rural tropical communities without access to modern surgical obstetrical care, the highest or one of the highest causes of death in childbearing women is childbirth.
• How can such an essential element to fitness pose such a high risk to both maternal and fetal survival?

8

Relative mismatch between newborn head size & maternal pelvic outlet size

• Two human features, upright locomotion and increased brain size, were (and are) both positively selected for to enhance fitness.
• The fitness benefit of both of these features is sufficiently strong to outweigh the fitness deficit of the significant maternal and infant mortality rate in childbirth due to the narrow pelvic inlet and outlet.
• Our understanding of this phenomenon is best illuminated through the study of hominin/hominid evolution.

9

Upright bipedal walking and increased brain size

• Two strongly selected traits through hominin evolution are upright bipedal walking and increased brain size.
• The earliest transition to facultative bipedal upright walking is documented to have occurred with Ardipethicus 4.4 million years ago.
• In hominins, the dramatic rate of increase in head circumference occurred later in the genus Homo, especially over the past 1.0-1.5 million years.

10

Hominin origins of upright walking

• Great apes mainly walk on all four extremities and walk on the knuckles of their hands.
• 4.4 million years ago Ardipethicus (Ardi) walked on all four extremities on palms of hands and was also a facultative upright bipedal walker but with anatomically flat feet.
• 3.2 million years ago Australopithecus (Lucy) was able to walk upright more effectively and had more arched feet than Ardi enabling easier upright bipedal locomotion.
• 2.5 million years ago with Homo habilis there was well developed upright walking which continued through all the Homo species with a increased ability to sprint and run long distances.

11

Possible reasons for the origin of upright walking and bipedalism

• Enhanced ability to forage and reach for food.
• Enhanced ability for hominins to carry things, including children and foods.
• Enhanced capacity for predator avoidance because individual can see further and run faster to escape predation.

12

Human pelvis

• Distinct shape of human pelvis compared to other apes because humans are bipedal and the mechanism of efficient upright walking and running have led to selection of relatively rotated hips and a relatively narrow pelvis.

13

Increased brain size & fitness

• Brain growth in hominin evolution appears to have been accelerated by selection for the benefits of larger brain size on fitness.

14

Selection for increased brain size appears to have enabled Homo species to develop the following

• Language
• Find adaptive advantage in social interactions within their group
• Enhanced tool making abilities

15

Percentage of resting metabolic rate for brain growth and function in Homo sapiens today

• Newborn infant uses about 85%.
• 5 year old child uses about 45%.
• Adults use about 20%.
• At each of these ages the % used is about twice that of a chimpanzee

16

Primate mean social group size relationship to relative neocortex volume

• Relative neocortex volume = neocortex volume/volume of rest of brain
• For different species of primates, including humans, there is a direct relationship between mean social group size and the relative neocortex volume
• The larger the social group size, the more complex the social dynamics are within the group
• The larger relative neocortex in humans has apparently enabled us to maintain a larger social group size.

17

Tradeoffs between relatively small pelvic diameter and relatively large newborn cranium

• To accommodate the increased brain size for labor and delivery, it would be adaptive to have an increase in pelvic outlet diameter.
• However, the selective pressure to maintain advanced bipedal upright walking and running prevents the Homo sapiens pelvic outlet from expanding to a diameter that would easily accommodate the relatively large head of the newborn Homo sapiens.
23

18

Trade-off: having a narrower pelvis for bipedal walking complicates ability to deliver large newborn head at birth

• Trade-off: human newborns have a large brain which makes delivery through narrower pelvis a challenge.
• If birth in humans occurred at the same stage of neuronal maturation as in apes who have a well-developed motor function at birth, the human head would be far too large to pass through the pelvic outlet.

19

Large human newborn brain

• If the human infant was born at the same stage of developmental maturity as other primates e.g., chimpanzees, the pregnancy would last about 21 months and this would require a pelvic canal so wide it would be impractical for efficient bipedal locomotion.

20

Neurologically immature newborns

• In response to the competing selective pressures of large newborn head and bipedal locomotion, Homo sapiens
have evolved to give birth to neurologically immature infants so the newborn head size can be better accommodated by the pelvic outlet size.

21

Newborn delivery solution to trade-off of having a narrower pelvis
for bipedal walking

• Other apes are precocial, having relatively mature offspring at birth capable of some independent activity.
• So the human newborn head can fit through the relatively narrower pelvic cavity, humans are born ‘early’, have developed secondary altricial characteristics and are extremely dependent on parents for a long period after birth.

22

Altrial characteristics of human infants

• The human infant is entirely dependent on its mother for the first two years and is not able to be independently fully mobile and able to run until age 3 or older.
• This prolonged support of infants, toddlers and children influences the human family and community structure.

23

Relatively small pelvic diameter and relatively large newborn cranium

• Even with this accommodation, the fit of the head through the pelvic cavity at birth is relatively tight resulting in the relatively high maternal and fetal death rate in cultures today that do not have access to cesarean section.

24

Comparison of newborn delivery in chimpanzee and humans

• In chimpanzees, their smaller heads readily pass through the pelvic outlet without the need for the twisting and turning (Fig 7.8).
• Compared to chimpanzees, the human fetus is born relatively immature neurologically so the head fits through the pelvic inlet, however, this is only possible with considerable twisting and turning of the head during delivery (Fig 7.8).
• As a result, in contrast to other primates, the human newborn head is typically delivered facing to the dorsal aspect of the mother.

25

Upright bipedal walking, increased brain
size, & neurologically immature at birth

• The earliest transition to facultative bipedal upright walking is documented to have occurred with Ardipethicus 4.4 million years ago; resulted in a relatively narrow pelvic outlet/inlet (anatomic constraint)
• In hominids, the most dramatic rate of increase in head circumference occurred later in the genus Homo erectus, especially over the past 1.0-1.5 million years.
• In order for the larger Homo sapiens head to more easily fit through the relatively narrow pelvic outlet, babies are born neurological immature (altricial)

26

Female vs male human pelvis

Human female pelvic features for childbirth Compared to males, females have:
• larger, more oval pelvic inlet
• wider pubic symphysis
• wider pubic arch (>90º)
• outward turning of the ischial tuberosities
• (last three features produce a larger pelvic
outlet)

27

Mismatch with approaches to labor & delivery influencing C-section rate

• Today, pregnancy and child birth continues to be a significant cause of death in women of child-bearing ages in regions of the world that do not have modern obstetrics.
• Even with modern obstetrics and supportive labor environments, 2-3 % of deliveries require C-section because the anatomically constrained pelvic size would result in maternal and/or infant death if vaginal delivery was attempted.

28

Imperfect system for labor and delivery in humans

• This highlights the imperfect system for labor and delivery of the relatively large human newborn heads due to tradeoffs in the development of bipedal locomotion resulting in a small pelvic inlet and outlet.

29

Regulation of fetal growth and maternal constraint

• Maternal constraint in pregnancy includes the limitations to the capacity of how much the utero-placental unit can supply nutrients to the fetus.
• Hence, fetal growth is not solely controlled by genetics, but rather a combination of fetal genetics and the intra-uterine environment.

30

Birth weights, parents & relatives

• An examination between birth weights of first degree relatives demonstrates a higher inter-pair correlation between half-siblings who share the same mother compared to half-siblings who share the same father (Table 7.1)

31

Birth weights, parents & relatives

• Thus, paternal factors tend to play little direct role in directing fetal and newborn size.
• However, adult body size is highly correlated with maternal and paternal size and hence is from a blend of maternal and paternal genetic contributions.

32

Regulation of fetal growth

• Fetal growth is directly regulated by supply of nutrients across the placenta, which influences the levels of insulin and insulin-like growth factor 1 (IGF-1).
• Fetal growth is a balanced link between fetal genetics and maternal placental nutrient availability which is influenced by maternal size.
• Thus, size at birth in humans correlates much more with maternal stature and maternal birth weight and than with paternal stature or birth weight.
• From an evolutionary standpoint considering the difficulties humans already have with the size of the pelvic outlet, this makes labor and delivery of a fetus with a tall father and a short mother safer and more feasible.

33

Regulation of fetal growth in
horses and ponies

• Maternal size constraint is demonstrated in research on crosses between large Shire horses and small Shetland ponies (Fig 7.7)
• When a small Shetland father was crossed with a large Shire mother the fetuses grew much larger compared to the fetuses resulting from a cross between small Shetland mother was crossed with a large Shire father.

34

Cross-cultural studies of indigenous cultures around the world: birth positions and environments

• Women in these cultures go through labor and birth in different types of upright positions.
• Women in these cultures are supported and cared for in labor and delivery by a female midwife.
• Perhaps early Homo sapiens as well as earlier hominin groups had similar social support systems and birth positions for labor and birth.

35

1st and 2nd stages of labor

• 1st stage of labor: when fetus is still in uterus and its head has not yet passed out of the uterus through the cervix into the vagina
• 2nd stage of labor: full cervical dilation to 10 cm and full cervical effacement which allows the head of the fetus to pass through the cervix into the vagina and through the pelvic outlet.

36

Factors that influence Stage 1 of labor

• strength of uterine contractions
• how much cervix effaces and dilates
• Ancestral labor environment matches and mismatches influence the strength of uterine contractions and how much cervix effaces and dilates which influences how stage 1 of labor progresses.

37

Evolutionary pathways that influence Stage 1 of labor

• ancestral labor environment matches and mismatches influence how stage 1 of labor progresses.
• outcomes of cultural history influences labor environment

38

Factors that influence Stage 2 of labor

• strength of uterine contractions
• size of pelvic inlet and outlet

39

Evolutionary pathways that
influence Stage 2 of labor

• ancestral labor environment matches and mismatches influence strength of uterine contractions
• ancestral labor environment matches and mismatches influence size of pelvic inlet and outlet during labor
• outcomes of cultural history influences labor environment
• outcome of anatomical constraint influences size of pelvic inlet and outlet

40

Case 1a

• 25 year old healthy primigravida female with labor arrested in 1st stage has a C-section.

41

25 year old healthy primigravida female

• 25 year old normal weight healthy primigravida female who eats well and has had regular exercise before her pregnancy and moderate exercise (regular walking) during her pregnancy.
• She has had excellent prenatal care both with her obstetrician and has had no problems with her pregnancy.
• She has elected to NOT have a doula (labor support person) with her during the labor and delivery.
• She expects that she will elect to use pain medications, e.g., an epidural injection, during labor.
• She has a supportive husband and a supportive extended family in the area.
• She and her husband own a home and are financially stable.

42

25 year old healthy primigravida female in labor with term pregnancy

• Her due date at 40 weeks gestation was three days ago and on that day an ultrasound revealed that the female fetus was healthy and estimated the weight to be between 7.5 to 8 pounds.
• Yesterday, after laboring for 12 hours at home, she was driven to the hospital by her husband and was admitted onto the labor unit.

43

25 year old healthy primigravida female in labor with term pregnancy

• The admitting physical exam in the hospital was done by the obstetrician and found that the cervix was not dilated and only minimally effaced indicating 1st stage of labor; fetal heart rate was normal.
• Mom reported that the pain from the contractions was severe and she was offered and received an epidural injection to treat the pain.
• A fetal heart monitor was set up which required her to stay in bed on her back most of the time as she continued her labor.
63

44

25 year old healthy primigravida female with labor arrested in 1st stage has a C-section

• Her contractions continued through the night, but were not as a strong as they had been at home and the mom reported that she was quite exhausted.
• On PE the following day, the obstetrician found that the cervix was not dilated and only minimally effaced with minimal change compared to PE on admission and she was still in 1st stage of labor; fetal heart rate demonstrated mild decelerations during contractions.
• Diagnosis: labor arrested in 1st stage of labor.• Because the mom was exhausted with the labor arrested in 1st stage along with the fetus demonstrating mild deceleration of heart rate with uterine contractions, a C-section was suggested, accepted, and performed.
• The mom and the newborn female did fine post C-section.

45

Case 1a: 25 year old healthy primagravida female with labor arrested in 1st stage has a C-section.
• What evolutionary pathway(s) may have contributed to this woman having a C-section?


Evolutionary Pathways to Disease and/or Health
• An evolutionary matched environment.
• An evolutionary mismatched or novel environment.
• Outcomes of demographic history.
• Outcomes of cultural history. • Outcome of evolutionary constraints.
• Sexual selection and “sexual”competition and their
consequences.
• Life-history and/or developmental associated factors.
• Antagonistic pleiotropy.
• A harmful allele when homozygous is maintained by heterozygote
advantage.
• Effects of deleterious allele does not become apparent until after reproductive age.
• Spontaneous mutations for a deleterious gene defect replace alleles eliminated by selection.
• Exaptation.
• Excessive and uncontrolled defense mechanisms.
• Fighting the evolutionary arms race with microbes.

46

C-section rates today

• C-section rate today at Dublin Maternity hospital in Ireland is 2-3% and nearly all deliveries are by midwives.
• C-section rate was 5% in USA in 1970.
• C-section rate is >30% in USA in 2015.
• C-section rates are over 90% in some
hospitals in China and Brazil.

47

Reasons for high C-section rate

• Lawsuit risk create low thresholds for doing C-sections.
• Use of pain drugs e.g. epidural injections, during labor which inhibit labor.
• Continuous fetal monitoring with probe increases the likelihood of C-section.
• Stressful hospital environments inhibit labor by increasing stress hormones and triggering the sympathetic nervous system response.
• Lack of nurturing support during labor can inhibit labor.
• Laboring and delivering on back increases fetal stress and inhibits progress of labor.

48

Reasons for high C-section rate

• Increased BMI (body mass index) of women delivering babies in USA increases C-section rate.
• Low vitamin D levels in pregnant mom increases risk for having C-section.
• Some women choose to have a C-section because they do not want to go through a vaginal delivery, however, recovery time and potential morbidity is much higher for C-section deliveries than vaginal deliveries.
• Some C-sections are medically necessary (2-3% of births) and save both the mom’s and the infant’s life.

49

Fetal stress, lawsuits, & C-section rate

• C-sections are done to avoid being sued if a child is delivered vaginally who has some brain problem.
• Hence, even slight indication of fetal stress triggers a C-section even though slight fetal stress has NOT been demonstrated to increase risk for cerebral palsy.
• When comparing 1970 and 2010 in the USA, the rate of newborns with cerebral palsy and other brain injuries is unchanged despite the 600% increase in C-section rate over this time period.

50

Continuous Monitoring of Fetal Heart Rate

Continuous heart monitoring of infant if achieved by screwing a small monitor into the fetal scalp

When continuous fetal monitoring was instituted in USA ® doubled the cesarean section rate, but resulted in no reduction in the incidence of cerebral palsy

Nine separate studies throughout world have not shown any improvement in outcome for the baby with continuous fetal heart monitoring in healthy women

Prevents mom from walking during labor therefore decreases beneficial effects of gravity on labor therefore increases length of labor therefore increase rate of C-section by 2X

Since continuous fetal monitoring was instituted in USA:
® doubled the cesarean section rate
® resulted in NO reduction in incidence of cerebral palsy

51

Epidural Analgesia

Opiates are frequently given by epidural injection to numb pain of uterine contractions during delivery:
-decreases mothers own endogenous production of endorphins
-decreases mothers ability to feel the natural urge to push in labor
-decreases mothers sense of control over labor
-decreases mothers sense of accomplishment of delivering her baby
-decreases mothers production of oxytocin & decreases mothers ability to push therefore increases length of labor therefore increase C-section rate

52

Doula (birth support person)

• Doula is a woman who supports the mother during labor and delivery
• Having a trained doula during labor and delivery has been demonstrated to significantly decrease the likelihood of a mom having a C-section.

53

Doula Supported Deliveries based on 7 randomized clinical trials

-decreases length of labor by 25%
-decreases exogenous oxytocin use by 40%
-decreases pain medication by 60%
-decreases forceps use by 40%
-decreases C-section rate by 50%

54

Mismatch between ancestral and modern hospital labor & delivery positions influences C-section rate

• Studies of hundreds of traditional cultures have demonstrated that these cultures universally employ different upright positions e.g., squatting, to use gravity to facilitate delivery.
• In anthropological studies of over 70 cultures around the world, there are NO examples where women deliver on their backs.

55

Advantages of labor and deliver in an upright/crouched position

• Utilizes the benefits of gravity to ^ strength of uterine contractions and therefore decrease length of labor therefore decreases likelihood of C-section
• Increases surface area of pelvic opening/birth canal by 33-38%
• decreases pressure on mothers aorta (largest artery) which increases blood supply to the fetus therefore decreases likelihood of fetal stress

56

Mothers who labor/deliver on backs compared to upright position:

• Less comfortable for mothers
• decreases benefits of gravity for labor therefore decreases strength of uterine contractions therefore ^ length of labor therefore ^ likelihood of C-section
• decreases benefits of gravity for labor therefore decreases opening of pelvic cavity/birth canal
• ^ pressure on mothers aorta (largest artery) which may reduce blood supply to the fetus therefore ^ likelihood of fetal stress therefore ^ likelihood of C-section

57

Upright positions in labor

• When women deliver in an upright position, their pelvic outlet opens up 33-38% more and they have stronger uterine contractions than women delivering on their backs.
• Women who deliver on their backs instead of in an upright position have a higher likelihood of having a C-section.
• Hence, with women delivering on their backs, there is a mismatch with our ancestral birthing positions resulting in an increased risk of having a C-section.

58

Vaginal deliver complications
and C-section rates

• Potentially fatal labor & birth complications occur in 2-3% of deliveries and require C-section.
• The source of the vaginal delivery difficulties in 2-3% of the pregnancies is due to the pelvic anatomical constraint because the ability for upright bipedal locomotion has constrained the size of the pelvic inlet and outlet making it difficult or impossible for the large infant brain to fit through the inlet and outlet.

59

C-section rates today

• C-section rate today at Dublin Maternity hospital in Ireland is 2-3% and nearly all deliveries are by midwives.
• C-section rate was 5% in USA in 1970.
• C-section rate is >30% in USA in 2015.
• C-section rates are over 90% in some hospitals in China and Brazil.

60

Vaginal deliver complications and C-section rates

• High C-section rate (30%) is a mismatch between ancestral environment and modern environment for labor and delivery.

61

Case 1a: 29 year old healthy primigravida female with labor arrested in 1st stage has a C-section.
• What evolutionary pathway(s) contributed to this woman having a C-section?

• An evolutionary mismatched or novel environment: mismatch between ancestral birth environment and birth environment today.
• The outcome of cultural history.

62

Case 1a: Environmental mismatches of birth environment in this 25 year old healthy primigravida female with labor arrested in 1st stage has a C-section.

• No labor support person (doula).
• Epidural injection.
• Continuous fetal monitoring.
• Labored on her back and not in upright positions.
• All these are examples of environmental
mismatches that increase the risk of C-section compared to the ancestral birthing environment.

63

Case 1a: Outcome of cultural history in this 25 year old healthy primigravida female with labor arrested in 1st stage has a C-section.

• The family and cultural environment of this patient likely influenced her to not choose a doula, not attempt to avoid receiving an epidural injection, and not choose to labor in an upright position.
• All these choices generated a mismatch between the ancestral birth environment and the birth environment for this woman today, resulting in an increased likelihood of having a C-section delivery.

64

Case 1b

• 25 year old healthy primigravida female with normal spontaneous vaginal delivery of a term gestation female.

65

25 year old healthy primagravida female

• 25 year old normal weight healthy primigravida female who eats well and has had regular exercise before her pregnancy and moderate exercise (regular walking) during her pregnancy.
• She has had excellent prenatal care both with her obstetrician and has had no problems with her pregnancy.
• She has elected to have a doula (labor support person) with her during the labor and delivery.
• She plans to labor in a variety of upright positions.
• She hopes to not use any pain medications, e.g., an epidural injection, during labor.
• She has a supportive husband and a supportive extended family in the area.
• She and her husband own a home and are financially stable.

66

25 year old healthy primagravida female
in labor with term gestation pregnancy.

• Her due date at 40 weeks gestation was three days ago and on that day an ultrasound revealed that the female fetus was healthy and estimated the weight to be between 7.5 to 8 pounds.
• 12 hours ago mom went into labor. She has gone through much of this labor in different upright positions in the relaxed environment of her home with her husband and a trained labor support person (doula).
• Since uterine contractions were getting progressively stronger and more frequent she and her doula were driven by her husband to the labor unit at the hospital.

67

1st and 2nd stages of labor

• 1st stage of labor: when fetus is still in uterus and has NOT yet passed out of the uterus through the cervix into the vagina.
• 2nd stage of labor: full cervical dilation to 10 cm and full cervical effacement which allows fetus to pass through the cervix into the vagina and through the pelvic outlet.

68

25 year old healthy primigravida female with a normal spontaneous delivery of a term gestation pregnancy.

• On physical exam in the hospital, the obstetrician found that the cervix was completely effaced and dilated to 9 cm; complete dilation of cervix is typically 10 cm.
• Mom was admitted to the labor floor in hospital and continued labor in a variety of upright positions.
• She continued to have frequent strong contractions and within one hour her labor progressed to the second stage with infant passing through the cervix into the vagina.
• Two hours after being admitted into the labor unit, mom had a normal spontaneous delivery of a healthy newborn daughter while she was positioned in an upright crouched position.

69

Case 1b:
What evolutionary pathway(s) contributed to this normal spontaneous vaginal delivery of a female infant?

Evolutionary Pathways to Disease and/or Health
• An evolutionary matched environment.
• An evolutionary mismatched or novel environment.
• Outcomes of demographic history.
• Outcomes of cultural history. • Outcome of evolutionary constraints.
• Sexual selection and “sexual”competition and their
consequences.
• Life-history and/or developmental associated factors.
• Antagonistic pleiotropy.
• A harmful allele when homozygous is maintained by heterozygote
advantage.
• Effects of deleterious allele does not become apparent until after reproductive age.
• Spontaneous mutations for a deleterious gene defect replace alleles eliminated by selection.
• Exaptation.
• Excessive and uncontrolled defense mechanisms.
• Fighting the evolutionary arms race with microbes.

70

Case 1b: What evolutionary pathway(s) contributed to this normal spontaneous vaginal delivery of a female infant?

• A match between the ancestral birth environment and the birth environment for this woman today.
• The outcome of cultural history.

71

Case 1b: A match between the ancestral birth environment and the birth environment for this woman today.

• Chose to have a doula (labor support person), with her during the labor and delivery.
• Chose to labor in a variety of upright positions.
• Chose to not use any pain medications, e.g., an epidural injection, during labor.
• All of these choices contributed to generating a match between the human ancestral birth environment and the birth environment for this woman today, resulting in an increased likelihood of a vaginal delivery.
• She is also one of the 97-98% of women who, if under supportive conditions, can have a safe vaginal delivery.

72

Case 1b: Outcome of cultural history in this 29 year old healthy primagravida female with normal spontaneous vaginal delivery of a female infant

• The family and cultural environment of this patient likely influenced her to choose a doula, choose to labor in an upright position, and avoid receiving an epidural injection.
• All these choices contributed to generating a match between the human ancestral birth environment and the birth environment for this woman today, resulting in an increased likelihood of a vaginal delivery.

73

Case 1c

• 25 year old healthy primigravida female with arrested early 2nd stage of labor of term gestation pregnancy.

74

25 year old healthy primigravida female

• 25 year old normal weight healthy primigravida female who eats well and has had regular exercise before her pregnancy and moderate exercise (regular walking) during her pregnancy.
• She has had excellent prenatal care with her obstetrician and has had no problems with her pregnancy.
• She has elected to have a doula (labor support person) with her during the labor and delivery.
• She plans to labor in a variety of upright positions.
• She hopes to not use any pain medications (e.g., an epidural injection) during labor.
• She has a supportive husband and a supportive extended family in the area.
• She and her husband own a home and are financially stable.

75

25 year old healthy primigravida female
with labor that is not progressing

• Her due date at 40 weeks gestation was three days ago and on that day an ultrasound revealed that the female fetus was healthy and estimated the weight to be between 7.5 to 8 pounds.
• Two days ago mom went into labor and has gone through much of this labor in a variety of different upright positions in the relaxed environment of her home with her husband and a trained labor support person (doula).
• Since the labor was not progressing and mom was getting tired, she and her doula were driven by her husband to the labor unit at the hospital.

76

25 year old healthy primigravida female
with arrested early 2nd stage of labor of term gestation pregnancy.

• On physical exam in the hospital, the obstetrician found that most of the head of the infant had moved through the cervix which represents the early 2nd stage of labor.
• Mom was admitted to the labor floor in hospital and continued to have regular contractions and labored in a variety of upright positions.
• Over the next 12 hours she was regularly examined, and the position of the fetus remained unchanged and she was diagnosed with an arrested 2nd stage of labor.
• At 12 hours post admission it was determined that during uterine contractions the fetus’ heart rate was dropping down dramatically.

77

25 year old healthy primigravida female with arrested early 2nd stage of labor of term gestation pregnancy.

• Because of the potential danger to the fetal blood supply associated with dramatic drops in heart rate during uterine contractions, along with the arrested state of labor in the early 2nd stage, a STAT C-section was performed.
• The mom and the newborn female did fine post C-section.

78

Case 1c:
What evolutionary pathway(s) contributed to this woman’s labor being arrested in the early 2nd stage of labor?

Evolutionary Pathways to Disease and/or Health
• An evolutionary matched environment.
• An evolutionary mismatched or novel environment.
• Outcomes of demographic history.
• Outcomes of cultural history. • Outcome of evolutionary constraints.
• Sexual selection and “sexual”competition and their
consequences.
• Life-history and/or developmental associated factors.
• Antagonistic pleiotropy.
• A harmful allele when homozygous is maintained by heterozygote
advantage.
• Effects of deleterious allele does not become apparent until after reproductive age.
• Spontaneous mutations for a deleterious gene defect replace alleles eliminated by selection.
• Exaptation.
• Excessive and uncontrolled defense mechanisms.
• Fighting the evolutionary arms race with microbes.

79

Two fundamental differences when comparing humans to other apes is that humans have developed

• Upright bipedal locomotion.
• Substantially increased brain size/body size ratio.

80

Which evolutionary pathway

• A tradeoff in the development of bipedal upright locomotion and an increased head circumference has resulted in anatomical constraints in size of pelvic inlet and outlet.
• The interaction of these two evolutionary innovations (upright locomotion and increased brain size) in humans has resulted in
anatomical constraint of size of pelvic inlet and outlet in relationship to the size of human newborn heads making it difficult or impossible for some (2-3%) of term babies to be delivered vaginally.

81

Fitness benefit from upright locomotion and increased brain size versus fitness deficit from high childbirth mortality

• Two human features (upright locomotion and increased brain size) were (and are) both positively selected for to enhance fitness.
• The fitness benefit of both of these features is sufficiently strong to outweigh the fitness deficit of the relatively high maternal and infant mortality rate in childbirth due to the narrow pelvic inlet and outlet.
• Evolutionary Pathway is result of evolutionary constraint.