Ontogeny Flashcards
What is the recapitulation theory
(E. Haeckel, 19th): « ontogeny recapitulates phylogeny ». • Now refuted: similarities with embryos at the same stage, but not ancestral
adult forms.
more accurate = successive developmental steps correspond to adult forms that appeared during the evolutionary history
What is ontogeny
all of the stages of life that precede the cessation of growth.
Define the following
Heterochrony:
Heterotopy
Heterochrony: change in time or rate of development of a feature.
• Heterotopy: change in the spatial arrangement of a feature.
define paedomorphy and peramorphy
paedomorphy
truncating the ancestral ontogenetic trajectory, adults retain juvenile features
peramorphy
extending the ancestral ontogenetic trajectory
What can lead to paedomorphy
- postgenesis: earliest offset
- postdisplacement: delayed onset
- neoteny: reduced rate
what can lead to peramorphy
- hypermorphosis: delayed offset
- predisplacement: earlier onset
- acceleration: increased rate
By what age are chimps vs humans adults
adult = all teeth emerged, all bones fused, first reproduction
chimp = transition at 13-15yrs human= 17-19 years
What are the key post-birth LH stages in most primates
• Infancy stage: from birth to the emergence of the M1, weaning, brain growth
completed in most primates.
• Juvenile stage: considerable growth and development.
• Adulthood: reproduction, eruption of all permanent teeth (including M3), postcranial growth completed.
What are the key post-birth LH stages in humans
- Infancy stage: from birth to the emergence of the M1, weaning, brain growth completed in most primates.
- Childhood: prior to the emergence of permanent teeth, brain growth continues after weaning.
• Juvenile stage: considerable growth and development.
• Adolescent growth spurt: growth spurt after puberty, skeletal growth
acceleration (M2 eruption).
• Adulthood: reproduction, eruption of all permanent teeth (including M3),
postcranial growth completed.
post reproductive in females
What do you call human child helplessness
secondary altriciality
humans at birth are more immature and helpless than other apes, require more parental care
How does human brain at birth compare to chimps
Compared to other great apes humans: a smaller brain at birth, faster and
prolonged brain growth.
chimp: at birth: 1/3 adult brain size
human: at birth: 1/4 adult brain size
What are the key ways to investigate LHS in the fossil record
teeth:
→ eruption pattern
→ dental histology
→ elements & isotopes
skull: → brain shape → brain size → suture fusion → bone histology
post-crania:
→ suture fusion
→ bone histology
Give the timing of dental eruption in chimps vs humans
chimps: M1 at 2.66-4.08 years
humans: M1 at 4.74-7.00 years
Give the sequence of dental eruption in chimps vs humans
chimps: M1-I1-I2-M2-(P3,P4)-C-M3
humans: M1-I1-I2-(P3,C,P4)-M2-M3
How are teeth formed
wat are key cells involved
- Tooth formation: incremental growth from the dentinoenamel junction.
- Ameloblasts: cells that deposit enamel.
- Odontoblasts: cells that deposit dentine.
What are key marks of growth on the teeth
• Short-period lines: daily increments of enamel (cross striations) and dentine
(von Ebner’s lines) depositions.
• Longer-period lines: produced at regular intervals in enamel (Retzius lines) and
dentine (Andresen lines).
What are perikymata
surface manifestations of Retzius lines.
What is the neonatal line
• Tooth formation: neonatal line (darker and larger than the other lines).
How are teeth interesting for weaning
Trace element and isotope analysis in teeth: breastfeeding practices and
weaning age. • Teeth retain the isotopic and elemental dietary signals throughout ontogeny
How is the brain useful for assessing LHS
• Craniofacial growth: cranial sutures serve as sites of bone expansion
(intramembranous bone growth).
• Brain growth is closely related to craniofacial growth: new bone is produced in
response to stimuli, such as brain growth.
Describe long bone growth in length:
occurs at the epiphyseal (growth) plate that is made of cartilage at the distal end of long bones (endochondral ossification).
What does age of tooth emergence look like in early hominins
Tooth formation and eruption in early hominins: growth periods in Australopithecus, Paranthropus and early Homo are more ape-like and thus teeth formed more rapidly than in extant humans (Bromage and Dean, 1985;
Dean et al., 2001).
• Emergence of delayed maturation after the emergence of Homo
What did breast feeding look like in Austalopithecus
- Breastfeeding: a period of 12-13 months for Australopithecus africanus similar to extant humans (but perhaps extended depending on food availability?).
- Longer breastfeeding period in early Homo.
What did brain growth look like in afarensis
A comparison of infant to adult endocranial volumes indicates protracted brain growth in A. afarensis, likely critical for the evolution of long childhood learning
Describe the brain development of Taung child
aged 3-4 (M1 erupted) but has remnant of anterior fontanelle
in great apes, the MS normally fuses shortly after birth, such that unfused MS similar to Taung’s are rare. In humans, however, MS fuses well after birth, and partially or unfused MS are frequent. In gracile fossil adult hominins that lived between ∼3.0 and 1.5 million y ago, MS are also relatively frequent, indicating that the modern human-like pattern of late MS fusion may have become adaptive during early hominin evolution
Falk 2012
What may have been the selective pressures favouring delayed fusion in species such as africanus
three aspects of perinatal ontogeny:
(i) the difficulty of giving birth to large-headed neonates through birth canals that were reconfigured for bipedalism (the “obstetric dilemma”),
(ii) high early postnatal brain growth rates, and
(iii) reorganization and expansion of the frontal neocortex.
not mutually exclusive
Name a gene that is important in suture closure
What is interesting about this
RUNX2
Neanderthal genome provides evidence for positive selection in the modern human variant of RUNX2
how did P robustus mature
. As with other Plio-Pleistocene hominins, the odonto-postcranial maturational pattern of TM 1517 more closely fits an African great ape rather than the extant human pattern
How does crown formation of KNM-WT 15000 compare to other hominins
Dean 2001 using perikymata
Estimates of crown formation times for all anterior tooth types in KNM-WT 15000 fall consistently among those for australopiths and are shorter than those in our modern human sample
was only based off Nariokotome youth and Sangiran specimen
When is the first shift in enamel growth rates in human evolution
the first evidence for a shift in enamel growth rates in the hominin fossil record seems to be with the origin of larger-brained Neanderthals (at least by 100 kya) and modern human
When did molars emerge in erectus
M1 emergence occurred around 4 years of age in KNM-WT 15000, close to the time of enamel completion in the lower canines, as it does in modern humans (and Paranthropus).
This age is in broad agreement with another estimate (4.5 years) for average M1 emergence in African Homo erectus on the basis of mean endocranial capacity (826 ml) and implies an age at death for KNM-WT 15000 closer to 8 than 12 years of age
estimates of molar emergence times have shifted a little, in step with brain size, from those known for African great apes and australopiths
Why might enamel suggest habilis is not Homo
Dean 2001
results do not support the notion that the sequence of tooth development in H. erectus indicates that the timing of tooth development events was like that in modern humans, even though other sound nondental criteria suggest that the assignation to Homo is correct
however this is not true of habilis - tooth and post-cranial development different
What is the problem with Dean 2001 commenting on Nariokotome youth molars
data do not allow us to reconstruct a direct age for the emergence of molars M1 or M2, or an age at death for the Nariokotome or Sangiran specimens
What does the Dikika child suggest about Australopithecus LHS
a 3-year old Australopithecus afarensis, to adult fossils, it has been suggested that despite their ape-like endocranial volumes, members of this species took a longer time to attain the adult brain volume than African apes.
Describe the brain ontogeny of erectus
0.5-1.5 y/o Perning 1 (1.8-1.4mya) has been estimated between 630 and 663cc
Gona pelvis suggests 315cc at birth (Simpson, 2008)
rapid early human brain growth was already established in early H. erectus but 35% at birth is between chimp and human -> shorter period of brain growth in erectus cf. humans
must be taken with a pinch of salt as H erectus displays large variation in brain/body size across erectus populations even within a given geographical location
Hublin 2015
other sources say Perning 1 has cc of 52-79% of
adult Homo erectus variability (respectively for
adults values ranging between 800 and 1200cm3).
For comparison, modern humans have a value of
59,5% of adult endocranial capacity at 1 year and chimpanzee have a 80% adult volume at the same age (Balzeau, 2005)
VERY CONFUSING
How old is the Nariokotome Boy
developmental age = ~12y/o (upper deciduous canines still in place and unerupted third molars)
chronological age=~8y/o
enamel and dentine microstructures clearly shows that H. erectus individuals developed much faster than extant humans - closer to chimps
contrast between its skeletal development and actual calendar age seriously challenges the notion that H. erectus growth already exhibited a childhood slowdown and an adolescent spurt
Hublin 2015
How does neonatal brain size in Neanderthals compare to humans
382-416cc
~humans
How does brain ontogeny differ between humans and chimps
How does this compare to Neanderthals
globularisation phase in humans then same pattern of brain growth after eruption of deciduous teeth
Neandertals lack a postnatal globularization phase. However, after the eruption of the deciduous dentition modern humans, Neandertals and chimpanzees share a common—presumably ancestral—developmental trajectory with regard to endocranial shape changes
Which brain areas are particularly different in humans cf. Neanderthals
parietal
basal brain
temporal lobes, involved in language, memory and social functions, as well as the olfactory bulbs, are relatively larger in sapiens
How does Neanderthal tooth development compare to human
dental development occurred faster in Neandertals and/or that some phases of their somatic development were accelerated in comparison to extant humans.
Give details of a key Neanderthal fossil used to investigate LHS
Le Moustier 1
from skeletal and dental analysis = ~12y/o
based on already erupted teeth, it is predicted that he would have early eruption of M3 - early start to reproductive life
possibly relates to high mortality in young adults in Neanderthals (fast LHS)
Hublin 2015
When did Neanderthals stop weaning
using Ba/Ca ratios, exclusive breastfeeding until seven months followed by supplementation until total cessation of nursing at 1.2 years of age (Hublin, 2015)
More recent evidence suggests weaning began ~6 months (similar to humans)
highlights their similar metabolic constraints during early life, short IBI, and excludes late weaning as a factor contributing to Neanderthals’ demise. (Nava, 2020)
When should humans stop breast feeding
6 months according to WHO
Why does Bayle claim Neanderthal teeth take longer to develop
larger absolute dental size which may require more time for completion and development, and delayed relative calcification was suggested for the Neanderthal anterior dentition relative to the modern human condition
A unique pattern with an advanced mineralization of the M1 and delayed
maturation of the incisors
Bayle 2009
What did Smith claim about Neanderthal dentition
a simple Neandertal versus modern human dichotomy is inadequate to accommodate the morphostructural and developmental variation represented by Middle Paleolithic and earlier Upper Paleolithic populations.
Smith 2010
What did Romanova and colleagues claim about Neanderthal LHS
Neanderthal brain size at birth was similar to that in recent Homo sapiens and most likely subject to similar obstetric constraints. Neanderthal brain growth rates during early infancy were higher, however. This pattern of growth resulted in larger adult brain sizes but not in earlier completion of brain growth
. The pattern of Neanderthal brain growth fits into the general pattern of rate hypermorphosis in this species: Compared with rAMHS, Neanderthals have been shown to attain larger adult cranial sizes and more advanced (peramorphic) shapes within a given period of ontogenetic time
slower LHS than humans
How does Romanova and colleagues argue humans outlasted Neanderthals if they had bigger brains
It could be argued that humans growing smaller—but similarly efficient—brains required less energy investment and might ultimately have led to higher net reproduction rates. Such an evolutionary shift might have contributed to the rapid expansion of Upper Paleolithic AMHS populations into Eurasia
What does Zollikofer say of the evolution of erectus to Neanderthal brain
It appears that their voluminous brains evolved through allometric expansion of an H. erectus-like brain, while modern human brains evolved along a novel path-way involving expansion of the parietal cortex
Give a key divergence between sapiens and Neanderthal ontogeny
In all hominoids, the NS of the middle thoracic vertebrae and the atlas are the last to fuse, but in this Neandertal, it appears that fusion occurs ~2 years later than in modern humans (or closer to M1 root closure than to the M1 root being a quarter to half formed).
later fusion of the NS could reflect a decoupling of certain smaller-scale aspects of growth and maturation in these extinct humans in the transition from the childhood to the juvenile stage.
may be related to the characteristically expanded Neandertal torso or to ongoing growth of the neuraxis.
Is Neanderthal somatic growth pattern closer to erectus or sapiens?
sapiens:
Growth and development in this juvenile Neandertal fit the typical features of human ontogeny, where there is slow somatic growth between weaning and puberty (3, 28) that may offset the cost of growing a large brain
then growth spurt in adolescence (not in erectus)
Rosas 2017
How does Rosas’ research corroborate Romanova’s claims about Neanderthal LHS
El Sidrón J1 achieved 87.5% of full brain growth by 7.7years cf. 95% at 7yrs in humans
slower LHS and brain growth
What are the questions surrounding Naledi’s ontogeny
same maturational age as KNM-WT 15000 (unfused epiphyses, M3s unerupted), same age and mode of maturity or older with a slower maturation schedule like in Neandertals?
Which other skeletons is DH7 similar to
MH1 holotype of Au.sediba, dated to 1.98Ma (~10y/o)
KNM-WT15000 (H.erectus, 1.6Ma); (~8.5y/o)
all have unfused combination of unfused long bone epiphyses and pelvic elements and unerupted M3
How does the dental ontogeny of naledi compare to humans
Dentally, H.naledi appears to have a pattern of dental eruption which suggests an affinity with H.sapiens, with premolars fully emerged by the time the second molars are fully erupted; however, the pattern of dental root formation is more ape-like
What is confusing about the brain ontogeny of naledi
At 480-610cc, H.naledi has an intermediate brain-size between Au.sediba and H.erectus SMALL
H.naledi has a stature more similar to Au.sediba, estimated at 143.5cm for adults. If Au.sediba, H.erectus and H.naledi hareda similar modeof maturity, this would suggest an age at death for DH7 between ~8–11 years old
What does the teeth of naledi suggest about its place in the evolutionary tree
H. naledi deciduous molars do not consistently align with any genus or species in the comparative sample in either the crown shape or relative cusp analyses. This line of inquiry is consistent with other cranial and postcranial studies suggesting that H. naledi is unique.
Is there heterochronic change between afarensis and africanus
South African australopithecine crania are more pedomorphic than those of A. afarensis, similar to the contrast between chimpanzees and bonobos
What does the Taung child indicate about africanus growth
What are the implications of this
facial expansion from Taung to adulthood is comparable to facial expansion from Taung-aged chimps to adult chimps (McNulty et al., 2006).
This indicates that reduction in facial growth must have occurred earlier during life, be it prenatally or early during post-natal ontogeny
What does Zollikofer claim about sediba’s ontogeny
premaxillary suture in the juvenile individual (MH1) is still patent, indicating australopith-like sustained growth of the anterior dental arcade.
neurocranial and facial modules evolved relatively independently - mosaic
Give the cc and age of the following erectus specimens
a) Perning-1
b) Nariokotome boy
What did the Gona pelvis suggest for neonate cc
a) 0.5-1.5 y/o Perning 1 (1.8-1.4mya) has been estimated between 630 and 663cc
b) Nariokotome boy - 8y/o (~1.5mya), 880cc
Gona - 315cc (Simpson, 2008)
What does the size of the Gona pelvis suggest about erectus ontogeny
Gona pelvis suggests neonatal cc of 315cc (30-50% of adult, an intermediate value between that of chimpanzees (∼40%) and modern humans (∼28%))
suggests that H. erectus had a prenatal brain growth rate similar to that of humans but a postnatal brain and somatic growth rate intermediate between that of chimpanzees and humans
Give evidence of grandmother hypothesis in erectus
1) larger cc, later M1 eruption (4.5y/o), and increased body size (55-60kg ~50% increase on Au.) suggest delayed maturation and slowed LHS
2) marked change in climate ~1.9mya - (increased C4, decrease in frugivorous animals at this time)
3) before erectus hominins were restricted to (sub)tropical locations) but erectus went as high as latitude 50 degrees - this is the limit of tuber reliance in continental HGs
4) burnt patches with associated stone tools 1.5mya in East Turkana + reduced gut based on thoracic morphology (Aiello and Wheeler, 1995) -> investment in pre-consumption process
5) coincides with brain expansion and more complex social behaviours (edentulous Dmanisi, Acheulian gaze etc.)
6) can’t be sure of post-reproductive period but elders will always be unrepresented (Cave, 2014)
observations of Hadza women suggests appearance of grandmothers could have aided the success of
