Brain evolution Flashcards
what is a gyrus in the brain
a bulge
compare the brain sizes of extant humans and chimps
why is it useful to compare the brain anatomy
human: 1156–1775 cc
chimp: 282–454 cc
to see what is shared (because there is a shared LCA) and what is original to humans
What questions arise when we find something specific to human brains (that is absent in primate brains)
Why is it specific? What are the adaptations and why were they necessary?
Which areas are important for language
Wernicke’s and Broca’s areas
Where are a) Wernicke and b) Broca’s areas located
a) left temporal
b) left frontal
Give 2 critical functions of the frontal lobe
language
planning
How does Broca’s cap differ in humans from chimps
Broca’s cap is divided by two vertical sulci.
Chimp has only 1 furrow called the fronto-orbital sulcus
How does the occipital lobe differ in humans from chimps
extant humans have a reduced and more posterior visual cortex
What do we use to identify where the visual cortex is positioned in humans and chimps
lunate sulcus (Smith, 1903, claimed this was present in both species despite lunate sulci in humans being neither crescent shaped nor orientated in the typical way)
What did Black (1915) use to reaffirm the ideas of Smith that the visual cortex
there was some controversy about the homology of chimp and human lunate sulci so Black used the stria Gennari to provide further evidence
What does the position of the visual cortex in humans cf. apes suggest functionally
humans lunate sulcus is very posterior and therefore the visual cortex is reduced due to expansion of more rostral brain areas such as the association cortices
How does the human brain differ from the chimp brain
- Human is globular
* Chimp is elongated
What is an endocast
Why are they important
what can they show
how reliable are they
replica of the inner surface of the braincase. • Because brain tissues do not fossilize, endocasts are the only direct evidence of brain evolution.
Size
Shape
Organisation (cortical NOT subcortical)
endocasts are reliable proxies except noticeable differences on the top of the endocast.
How do you make an endocast (2)
physical endocasts made of dental molding material
virtual endocast using scanning (eg X-Ray)
What do you want to measure in a physical endocast? How do you do this?
size - water displacement
shape - linear measurements
organisation - coordinates
How can you do measurements on a virtual endocast
size- volumetric measurements
shape- surface comparisons
organisation- automated detection
What are the benefits of using measurements from a virtual endocast
• computer can work out volumetric measurements
• can compare different 3D models that have been generated
• organisation can be calculated with an algorithm
o more reproducible cf human measurements where results may differ between researchers
How did brain evolution change in the human trajectory
Before 0.6 Ma: brain size increase and body size increase (allometry). • From 0.6 Ma: brain size increase but no body size increase.
What is interesting about the brain size of small bodied hominins
Homo species with Australopithecus-like brain size. • Limited ressources might be responsible?
describe the Broca’s cap organisation in each of the following species and give the age of each species:
a) africanus
b) sediba
c) H rudolfensis
d) habilis
a) one branch (3.7(?)-2.2 Ma)
b) one branch but bulging? (2.0 Ma)
both of the above have chimp like organisation but sediba shows the beginning of some remodelling with the bulging?
c) 2 rami (2.1-1.8 Ma)
d) one branch (2.6-1.7 Ma)
o Earliest members of Homo had primitive brain- -Brain Cannot be used to define homo
Did the human-like frontal lobe organisation emerge along with the earliest
humans?
What was the organisation of Denisovan brains like
Very chimp like organisation not seen in later homo in Africa and Eurasia
When homo left Africa had primitive brain?
What did Bookstein 1999 suggest about the evolution of the human brain
what theory contrasts this
« stasis » in the evolution of the human
frontal lobes (Bookstein et al., 1999)
this used 2D measurements and was less accurate
Beaudet & Bruner, 2017, found Changes from ergaster to more recent homo and Frontal widening in humans and Neanderthals
What did the occipital of africanus and afarensis look like
• Africanus seems more human like (smaller and more posterior) while afarensis is more chimp like (bigger and more anterior)
o These are single individuals so we don’t know about variation
why is it interesting to see in which species the primary visual cortex is shifted posteriorly
shows parietal lobe expansion
o Did different parts of the brains evolve at different times?
This would reveal evolutionary pressures on species at the time
Where was the lunate sulcus placed in P. robustus and small bodied hominins
give the ages of each
give caveats for each
Paranthropus robustus
(2.3-0.9 Ma) = posteriorly placed
(Holloway, 1972)
not much data for Paranthropus
Homo naledi
(0.34-0.24 Ma)=
posteriorly placed
(Holloway et al., 2018)
Homo floresiensis
(0.95-0.17 Ma)=
posteriorly placed
(Falk et al., 2005)
both small bodied hominins have small brains but have derived organisation
What is interesting about the Neanderthal organisation of the occipital lobes
what does this suggest
Human-like position of the lunate sulcus BUT a specific position of the calcarine
sulcus (long and wide) that indicates a larger visual cortex.
o different improved(?) visual capabilities - due to different environment and selective pressures
Did the brain evolve as a bundle
Unsure
Mosaic-like evolution of the hominin brain: the occipital lobes re-organised
first in Australopithecus, followed by the frontal lobes in Homo.
however some argue for Concerted evolution of the hominin brain: emergence of a human-like
organisation of the frontal and occipital lobes in Homo.
Describe the shape of the Australopith brain
elongated
o Closer to chimps statistically
o But some regions (frontal) does seem more different between chimps and australopithecines
Describe the shape of Neanderthal brains
o Ancestral pattern of enlongated shape while sapiens is globular unlike erectus and neanderthal
o 2 different trajectories
o Extension of parietal only in modern humans - human specific parietal expansion and round shape (Bruner et al., 2003)
o Why differences?
Alleles associated with reduced globularity in Neanderthals but not in humans
• When did globularity emerge
o Compare different groups of modern humans of different ages
In very first humans – don’t have globular shapes – happened after this
• This key feature evolved quite recently
increasingly globular from 300kya (Jebel Irhoud) to 100kya (Qafzeh) to 10kya (Cro-magnon)
What did Gunz, 2019, find regarding alleles associated with endocranial globularity
what could this mean functionally
found that Neandertal alleles on chromosomes 1 and 18 are associated with reduced endocranial globularity. These alleles influence expression of two nearby genes, UBR4 and PHLPP1, which are involved in neurogenesis and myelination, respectively.
changes to basal ganglia and cerebellum are intriguing, because both brain structures receive direct input from the motor cortex and are involved
in the preparation, learning, and sensorimotor coordination of
movements
According to Gunz (2019) what structures may be affected by the reduced-globularity alleles seen in Neanderthals
basal ganglia
cerebellum
Expanded cerebellar interconnections with prefrontal, premotor, and superior-posterior parietal cortices, which also project densely to the putamen, may be particularly relevant to cognitive abilities of modern humans
In addition to
their involvement in sensorimotor coordination, what do the basal ganglia
also contribute to
why is this relevant to human evolution
diverse cognitive functions in memory, attention, planning, skill learning, and potentially to speech and
language evolution
Allelic changes leading to reduced brain globularity in Neanderthals may affect functioning of brain structures including basal ganglia and cerebellum
How does the cerebral blood flow change throughout hominin evolution
disproportionate increase in cerebral blood flow rate in hominins as seen from ICA
this matches increased brain size
Seymour (2016)
What are the 3 branches of the middle meningeal artery
what is the human configuration
anterior (ab), middle (mb) and posterior (pb) branches.
Human-like variation pattern: the mb may branch either to the ab or the pb.
Describe the middle meningeal vessel configuration in africanus and robustus
Australopithecus africanus (3.7(?)-2.2 Ma): human-like variation pattern (Beaudet et al., 2019)
Paranthropus robustus (2.3-0.9 Ma): human-like variation pattern (Beaudet et al., 2019)
Describe the organisation of middle meningeal vessels in erectus and Neanderthals
Homo erectus
(1.8-0.3 Ma):
ab and pb similarly developed (more reticulated)
Neandertal (0.197-0.039 Ma):
ab more developed
(Bruner et al., 2005)
What are the key venous sinuses that have been examined in hominins?
Describe the venous sinus structure in africanus and afarensis and boisei
Function?
The transverse-sigmoid (T-Si) and occipital-marginal (O-M) and venous sinuses.
Australopithecus africanus (3.7(?)-2.2 Ma): human-like T-Si > O-M (accessory)
Australopithecus afarensis (3.9-2.9 Ma)
Paranthropus boisei (2.5-1.2 Ma):
O-M > T-Si
(Falk and Conroy, 1983)
Different methods of cooling the brain?
What is the key general trend in Homo
Early humans have trend towards encephalization through heterochronic change
Describe the differences in adaptation between Homo and Paranthropus.
P = adapting to large teeth and muscles of mastication for different diets
Homo= little dental investment, invest in brain size per body mass
Habilis – beginning of trajectory of encephalization
How did Homo offset the metabolic costs of an encephalised brain?
Reducing energetic costs elsewhere: Reducing gut size – evolutionary trade off
Growth:
Cost of growth put onto mother – changing life history
Early homo grew faster than modern humans but showed beginnings of slowed life history
How did the openness of grasslands change in the Plio-Pleistocene transition in East Africa
What is the importance of this
extent of open grasslands peaks during the Pleistocene(,1.8–0.01 Myr ago)
more wooded conditions persisted longerin the Omo Valley (into the Late Pliocene, up to about 1.8 Myr ago)than in the lower Turkana Basin.
This expansion of grasslands across the Pliocene–Pleistocene transition has been linked to global climate change and major developments in the hominin clade, such as the more obligate bipedalism of Homo, increase in encephalization, and reduction in tooth and gut proportions
When efficient obligate bipedal hominins with multiple different dietary adaptations appeared, what were the consequences?
• Evolution of robust/megadont hominins
Invasion of carnivore niche
• Opposing selective pressures for specialist x
generalist strategies, endemic x pandemic
What is the archaeological evidence for culture emerging between 500 and 200kya
What is the importance
What biological changes may underlie this
greater regionality of artifacts
this period sees a greater emphasis of groups as units-
precondition for evolution of cultural capacity?
during this period almost 30% of hominin encephalization occurred - could relate to increased community size or may also have been selected for by the greater cognitive demand of maintaining social relationships over distance and time
Foley and Gamble 2009
What is the implication of rudolfensis’ position on Lieberman’s (2001) phylogeny?
Positions K. platyops as rudolfensis’ ancestor, making rudolfensis NOT homo – implies encephalization occurred in parallel in 2 separate lineages
When did encephalisation begin in hominins
Sahelanthropus (~360cc) and ardi (300-350) no different to chimp
suggests brain growth patterns didn’t emerge until Australopithecus
How does Australopithecus africanus’ brain size compare to chimps
Au. Afarensis and africanus both have the same average brain size as chimpanzees 400-420ml
Where was the lunate sulcus in afarensis
DIK-1-1 endocast has a clear and unambiguous impression of a lunate sulcus that is ape-like in both morphology and position. The lunate sulcus impression of the DIK-1-1 endocast falls exactly where it would be expected for a juvenile chimpanzee
Describe the argument between Falk and Halloway about lunate sulcus
re: AFRICANUS (Taung child)
Falk placed it anteriorly but Halloway used stereoplotting to show this location was impossible
Falk then claimed stereoplotting was inaccurate because it does not take shape into account so is not so useful for comparisons
by 2004 Holloway had showed posterior lunate sulcus in AFRICANUS using StW505 (<20mm from occipital pole)
How much smaller is the human V1
What does this allow for
121% than expected for primate of that body size
expanded posterior parietal cerebral cortex used for multimodal processing
What is a problem with using the lunate sulcus to assess brain organisation
inconspicuous and variable in humans
does not represent the anterior border of the primary visual cortex. (Zollikofer)
What can we learn from brain petalias about brain reorganization
Aficanus, boisei, and aethiopicus all have humanlike LORF Left-occipital right-frontal petalia
NOT seen in habilis so homoplasy rather than part of brian trajectory
Although also seen in great apes so might not represent reorganisation at all (de Sousa & Cunha, 2012)
How does Taung child’s development compare to humans
Comparison of the Taung Child fossil to the skull of a nine-year-old modern child suggest that A. africanus had a growth rate to adolescence more similar to that of modern apes
What is the ratio of blood supply to the brain from ICA: basilar arteries
ICA: basilar artery supply to brain =
85:15
What is the trend in carotid canal diameter throughout human evolution
Clear increase in metabolic demand throughout human evolution – clear non-allometric increase in Homo
o Increased synaptic transmission
Compare extant great ape ICA to that of Australopithecines
o QICA is up to two times higher in recent gorillas, chimpanzees and orangutans compared with 3-million-year-old australopithecine human relatives, which had equal or larger brains.
o there is an increase from ardi to africanus so some sort of trajectory
Describe how brain drainage adapted to bipedalism
- changes in position from supine/ quadrupedal to upright drastically increase pressure of lumbar CSF from -5cmH2O to 40cmH2O
- robusts and afarensis developed enlarged accessory sinus systems to aid brain drainage
What did de Sousa say of brain reorganisation prior to Homo (5)
Many aspects of humanlike endocast morphology make an appearance in Au. africanus, including
(1) evidence for a reduced V1,
(2) frontal lobes that are expanded orbitally and a prefrontal cortex that appears squared off rostro-laterally when viewed dorsally,
(3) anteriorly expanded, laterally pointed temporal poles,
(4) an incipient LORF petalial pattern, and
(5) a humanlike Broca’s cap region.
Although these features are not as pronounced as in humans, they can be interpreted as being derived in the direction of human (de Sousa 2012)
When compared with modern humans ,H. erectus brains display significant morphological differences. What do these include?
low brain height,
elongated and wider pro-portions,
less developed temporoparietal areas and narrower frontal lobes,
strong posterior projection of the occipital lobes, and
anterior positioning of the cerebellar fossa
What can we learn from the early brain development 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 (35% of adult cc)
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
What is the importance of symmetry in tools
What does it suggest cognitively
has not in extant species other than H. sapiens
symmetrical standardization of lithics signifies the ability to impose a pre-determined form on a piece of stone, and by extrapolation cognitive capacities for planning and perhaps language ability (Gowlett, 2006)
see also Acheulean gaze (Foley and Gamble, 2009)
Which hominins are associated with symmetrical tools
H. ergaster and African H. erectus. H. antecessor, H. heidelbergensis, floresiensisare, H. neanderthalensis, and early AMHS are also associated with symmetrical handaxes
