Speculative family tree:
- pre-humanoid ancestry:
- Common human ancestor (Africa 5m yrs ago)
the migration and diversification of Homo sapiens
European hunter-gatherers
Paleoneurology
- the cost of evolving the hominid brain
- Evolutionary changes of the cranium and brain size:
modern day micro-evolution

Evolution of Humans

Speculative family tree:

pre-humanoid ancestry:

pre-vertebrate evolution

eumetazoa (true tissues organized into germ layers, and an embryo that goes through a gastrula stage) ?Ediacaran c600-635mya
- bilateria (animals having a bilateral symmetry) ?585mya
  - deuterostomes (two mouths - first opening (the blastopore) becomes the anus) ~558mya eg. the < 1mm Saccorhytus ¹⁾
    - chordates (earliest fish Cambrian)
      - vertebrate fish

vertebrate evolution

vertebrate fish - 485-525mya (Cambrian explosion)
- gnathostomata (jawed fish, Ordovician)
  - eugnathostomata
    - teleostomi
      - osteichthyes (bony fish)
        
        sarcopterygii (lobe-finned fish) some developed spiracles (these evolved into ears) and lungs to breath air and then nostrils (such as the Gogonasus 380mya late Devonian)
        
        tetrapoda (4 limbed vertebrates with radius, ulna, humerus, femur, tibia, fibula, middle ear, spiracles, nostrils, lungs; 395mya)
        
        amphibian reptiliomorphs 340mya
        
        basal amniotes (egg equipped with an amnios)
        
        later amniotes
        
        primitive synapsid reptiles (the other group of amniotes evolved into sauropsida which evolved into modern reptiles and birds)
        
        eupelycosauria (pelycosaurs)
        
        sphenacodontia (caniniform teeth and thickened maxilla)
        
        therapsids 275mya (all non-therapsid pelycosaurs, as well as many other life forms, became extinct at the end of Permian period)
        
        neotherapsida (Permian onwards)
        
        theriodonts (“mammal-like teeth”) 265mya
        
        eutheriodontia (Middle Permian) - loss of teeth on the palate
        
        cynodonts (“dog-teeth”, Late Permian) - 260mya
        
        probainognathian
        
        prozostrodontia (Late Triassic)
        
        mammaliaformes (fixed dentition - primary and secondary teeth)
        
        mammalia (mammary glands)
        
        theriiformes (Mesozoic)
        
        eutheria (placentals) - 160mya
        
        boreoeutheria (most males have external testes)
        
        euarchontoglires (supraprimates including rodents)
        
        cobalamin synthetase gene from bacteria integrated to synthesize B12
        
        euarchonta (excludes rabbits, rodents)
        
        primatomorpha
        
        primates - 80mya
        
        haplorhines (dry nosed) - 63mya
        
        anthropoidea - 58mya
        
        catarrhini (Old World Monkeys) - 40 mya

primate evolution into humans

primitive insectivore mammals
- it is thought that increased levels of testosterone may have contributed to the increasing brain size seen in primates but then a reduction helped socialization of hominids
- Deleted in AZoospermia (DAZ) gene 1st appears 30-40mya
- pre-monkeys (anthropoids)
  - diet extended to fruit, nuts, leaves; eyes more anterior ⇒ 3D vision; manipulating limbs
  - originated in Asia 45mya, some migrated to Africa 38mya while a colder global climate 34mya resulted in extinction of most monkey-like anthropoids in Europe, Nth America and Asia (except the Bahinia banyueae in Asia) and instead lemur-like anthropoids dominated in Asia
  - New World monkeys - did not evolve to apes
  - Old World monkeys of Africa (25-35m yrs ago) - long, balancing tails; increasing body size; brachiating ⇒ arboreal; unlike all other mammals branching prior in the evolution tree, do not produce alpha galactose;
    - hominoidea (Apes) - 20.4mya - distinguished from other primates by a wider degree of freedom of motion at the shoulder joint as evolved by the influence of brachiation.
      - gibbons (~15-16mya) (Lesser Apes)
      - hominidae (Great Apes) (~15-16mya)
        
        forest-dwelling apes
        
        orangutans
        
        hunting apes (~15m yrs ago)
        
        gorillas 8.8mya (all have blood group type B)
        
        ? aquatic “naked ape” hunters:
        
        reduced hair, streamlined hair patterns & more erect posture for swimming
        
        hair remaining on head to prevent solar damage
        
        thick subcutaneous layer of fat to prevent heat loss
        
        improved hand capabilities to feel for food underwater
        
        homo-chimp ~ 6-8mya (split from gorillas and evolved cooperative aggression to maintain territories)
        
        chimpanzee 6.3mya (all have blood group type A)
        
        hominids - 6.3mya (split from chimpanzees)
        
        chimpanzee chromosomes 2A and 2B fused to form hominid chromosome 2
        
        over 80 chimpanzee genes were lost in human evolution including 36 for olfactory receptors, a type I hair keratin gene (perhaps lost 240,000yrs ago), sarcomeric myosin gene MYH16 (5.3mya perhaps resulted in smaller masticatory muscles) and CASPASE12, a cysteinyl aspartate proteinase which may have resulted in improved resistance to bacterial infection in humans
        
        natural selection resulted in Human accelerated regions in the genome such as HAR1F, which is believed to be related to brain development and HAR2 (a.k.a. HACNS1) which may be related to the opposable thumb.
        
        DAZ “doubled” about the same time that “Y Chromosome Adam” appears in human evolution
        
        Graecopithecus freybergi ~7.2mya fossils found in Greece, Bulgaria
        
        Sahelanthropus tchadensis ~7mya, fossils found in Chad
        
        chimp-sized human ancestor, Orrorin tugenensis, that walked upright 6m yrs ago in Kenya (disc. 2004)
        
        oldest found human ancestor “Toumai” (6-7m yrs ago) disc. in Chad in 2001
        
        Ardipithecus 5.6mya
        
        australopiths ~4-5mya
        
        enzyme which makes Neu5Gc, CAMH, is mutated 2.1-2.2mya hence huans do not make a common mammalian sialic acid (Neu5Gc), this may also have contributed to the increasing hominid brain
        
        Homo ~1.8mya
        
        Homo sapiens (modern human) 250,000-350,000 yrs ago (oldest fossil - Morocco 2017)

Common human ancestor (Africa 5m yrs ago)

Ardipithecus ramidus (Ethiopia 4.4m yrs ago)
Australopithecus anamensis (Kenya 4.2m yrs ago)
- use of stone tools commenced c 3.3mya in Kenya
- A. bahrelghazali (Chad 3-3.5m yrs ago)
- A. afarensis (Ethiopia, Tanzania 3.5 m yrs ago)
  - Paranthropus aethiopicus (Eastern Africa 2.7m yrs ago)
    - P. robustus (Sth Africa 2.5m yrs ago)
    - P. boisei (Eastern Africa 1.4-2.5m yrs ago)
  - A. garhi (Ethiopia 2.6m yrs ago)
  - A. africanus (Sth Africa 2-3m yrs ago) - 1st australopith to be discovered (in 1924); use of stone tools; oldest stone tools found outside of Africa, are 1.3-2.1m yrs old in Shangchen region of China perhaps made by an ancestor of H. erectus, while those found in Dmanisi, Georgia are dated to 1.85mya
    - H. rudolfensis (Eastern Africa 2m yrs ago)
    - hominids lose body hair and allows heat loss through perspiration to allow a more active lifestyle in hot environments and thus melatonin content of skin increases to protect from UV radiation and also reduces UV-A mediated breakdown of folate which is important for sperm and fetal neural tube development (c1.5-2mya)
    - those hominids who migrated into lower UV-B latitudes such as Eurasia ran into vitamin D deficiency issues with immune impairment and critically, ricket affected pelvis which would not allow births and thus melatonin content evolved to be reduced - not even Australia has enough UV-B to provide sufficient Vit D for the darkest skinned hominids without resorting to supplementary Vit D intake such as oily fish (eg. Inuits who evolved a heightened ability to tan to cope with high levels of reflected UV-A from snow and ice) or lichen-eating reindeer (eg. Finnish) - this effect occurred again with H. erectus and with H. neandertherthalensis and twice later with Homo sapiens migrating. When hominids re-invaded high UV zones, they evolved darker pigmentation again (eg. northern India H. sapiens moving to southern India 20,000yrs ago). Those who evolved in mid-latitudes of UV such as the Mediterranean (less than 40degN) gained the ability to tan.
  - 900,000yrs ago: 98.7% of hominids were wiped out leaving only 1280 breeding individuals to sustain a population for ~117,000 yrs according to genomic sequencing
    - this event was consistent with the fusion of two progenitor chromosomes, presently identified as chromosome 2 in extant human populations.
    - coincided with climate changes that turned glaciation into long-term events, a decrease in marine surface temperatures, and a possible long period of drought in Africa and Eurasia
    - helps explain the loss of African and Eurasian fossil evidence in the Early Stone Age
    - H. habilis (Sub-saharan Africa 1.8m yrs ago) - 1st found in 1960 in Tanzania
      - H. ergaster (Eastern Africa 1.7m yrs ago) - 1st hominid of essentially modern form; hominids reach Java/China by 1.8m yrs ago; hand axe;
        
        H. erectus (Sth Africa, Eastern Asia 2m-40,000 yrs ago)
        
        2mya fossil found in Drimolen cave system north of Johannesburg published in 2020²⁾
        
        likely used land bridges to reach Indonesia around 1 million years ago
        
        use of hafted stone-tipped spears for hunting commenced c500,000yrs ago
        
        H. floresiensis (Flores, Indonesia until 13,000 yrs ago ?until 16thC AD, disc. 2004) - small brain, 1m tall
        
        the island of Flores is also home to extant pygmies who appear to have Denisovan and Neanderthal DNA but no other archaic DNA evident suggesting their restricted height is a selection cause ³⁾
        
        H. luzonensis (Phillipines, 50-67,000ya)
        
        3-4' tall with premolars having two or three roots, similar to H. erectus, and very small molars with only single roots, and has curved finger and toe bones which resemble those of Australopithecus
        
        H. naledi (Sth Africa, ~300,000yrs ago; small brain, mixed primitive and modern features)
        
        H. antecessor (Spain ?1m-0.7m yrs ago)
        
        H. heidelbergensis (throughout Old World ?1m-0.6m yrs ago)
        
        H. denisova (?1mya to 30,000yrs ago) - Siberia to Papua New Guinea
        
        H. neandertherthalensis (Europe & Western Asia ?600,000-30,000 yrs ago)
        
        it appears inter-breeding with H. sapiens resulted in their defective Y chromosome being selectively replaced by H. sapiens' Y chromosome more than 100,000 yrs ago and it seems the common ancestor for both Y chromosomes i estimated to have been around 370,000 yrs ago.⁴⁾
        
        H. sapiens
        
        250,000-350,000 yrs ago in Africa; 40,000 yrs ago in Europe; to present
        
        earliest fossil record is 315,000 yr old fossil from Morocco, and a 210,000 yr old fossil from Greece (but this group appears not to have survived in this early wave of migration from Africa)
        
        use of bows and arrows for hunting commenced around 70,000yrs ago
        
        creativity; art; symbolic thought;language;

the migration and diversification of Homo sapiens

oldest known H.sapiens c300,000BC in Morocco (disc. 2017), although anatomically modern humans appear to have evolved in northern Botswana 160,000-240,000 yrs ago making the Moroccan dating incongruous.
120,000 yrs ago began cooking tubers and rhizomes to increase dietary starch in Sth Africa which presumably led to a duplication of the starch digestion genes
oldest known rock painting c71,000BC in Sth Africa
the Ice Age ( (100,000BC - 12,000BC) lowered sea levels and allowed easier migration in some areas such as the drying up of the North Sea (although the extensive glaciation would have made survival tough away from the tropics)
DNA analysis suggests humans migrated out of Africa 50,000-60,000 yrs ago in one migration:
- initially via the coast of India to Australia and New Guinea taking 5,000-6,000yrs, creating the Aboriginal population in Australia such as in Lake Mungo in 40,000-50,000 yrs ago - one of the first H. sapiens colonies outside of Africa.
  - the Polynesians migrated much later, starting around 3000BC and migrated from Taiwan region to eventually cover most of the Pacific Islands, and eventually to Hawaii
migrated to Europe reaching the Atlantic within 2,500yrs from the Balkans as follows, and presumably resulted in the demise of the indigenous Neanderthal population over some 6000 yrs (Nature Feb 2006):
- Middle East by 46,000BC
- Istanbul by 44,000BC
- Italy, and central Europe by 40,000BC
- Spain, France, and eastern Europe by 39,000BC
- world's earliest cave paintings (SE France) dated at 29,000-34,000BC
reached Madagascar ~8000BC
see http://www.duerinck.com/migrate.html and http://noel.mcn.org/GeneticMigration.htm
18 daughters of Eve:
- almost all American Indians have mtDNA that belong to lineages he named A, B, C and D
- Europeans belong to lineages H through K and T through X
- Asia the ancestral lineage is known as M, with descendant branches E, F and G
- In Africa there is a single main lineage, known as L, which is divided into three branches. L3, the youngest branch, is common in East Africa and is believed to be the source of both the Asian and European lineages.
  - the oldest of this maternal mitochondrial lineage, L0, of anatomically modern humans, is believed to have originated in northern Botswana 165,000 to 240,000yrs ago⁵⁾, from here they dispersed north-eastwards and south-westwards around 110,000-130,000 yrs ago when increased humidity led to green corridors being opened. Further migration to east Africa occurred 60,000-70,000yrs ago
7 European daughters of Eve based on mitochondrial DNA studies - all descended from the Lara clan - one of 3 clans still existing in Africa:
- Helena: This clan lived in the ice-capped Pyrenees. As the climate warmed, Helena’s descendants trekked northward to what is now England, some 12,000 years ago. Members of this group are now present in all European countries.
- Jasmine: Her people had a relatively happy life in Syria, where they farmed wheat and raised domestic animals. Jasmine’s descendants traveled throughout Europe, spreading their agricultural innovations with them.
- Katrine: Members of this group lived in Venice 10,000 years ago. Today most of Katrine’s clan lives in the Alps.
- Tara: Sykes’ maternal ancestry goes back to this group, which settled in Tuscany 17,000 years ago. Descendants ventured across northern Europe and eventually crossed the English Channel.
- Ursula: Users of stone tools, Ursula’s clan members drifted across all of Europe.
- Valda: Originally from Spain, Valda and her immediate descendants lived 17,000 years ago. Later relatives moved into northern Finland and Norway.
- Xenia: Her people lived in the Caucasus Mountains 25,000 years ago. Just before the Ice Age, this clan spread across Europe, and even reached the Americas. [As Dr. Wallace discovered, the X pattern is a rare European lineage and is also among the northern Native Americans such as the Ojibwa and Sioux.]
10 sons of a genetic Adam based on Y chromosomal analysis:
- I, II, III are found almost exclusively in Africa
- III's sons' lineage migrated to Asia and fathered sons IV-X
- IV - Sea of Japan
- V - northern India
- VI and IX - South Caspian
10 founding fathers of Europeans:
- three waves of migrations to Europe: 40,000, 22,000, and 9,000 years ago.
- 95% of European men can trace themselves to 1 of 10 male ancestors
- More than 80 percent of European men inherited y-DNA from Paleolithic ancestors who lived in Europe 25,000 to 40,000 years ago
- The other twenty percent inherited from Neolithic farmers in Europe 9,000 to 10,000 years ago
gene for thallaesemia identified in a hunter-gatherer Vietnamese man 7000yrs ago suggesting malaria was an issue in SE Asia before farming practices commenced⁶⁾

European hunter-gatherers

modern humans left sub-Saharan Africa at least 60 thousand years ago (ka), and during their initial expansion into Eurasia, they genetically mixed with Neanderthals, resulting in 2–3% Neanderthal ancestry in the majority of present-day non-African population
modern humans have populated Europe for more than 45,000 years
- Genomic data have shown that modern humans were present in western Eurasia at least 45 ka and mixed with Neanderthals
- Surprisingly, however, none of those pre-40 ka individuals left substantial traces in the genetic makeup of present-day Eurasian populations and appear to have become extinct
- The oldest genomes carrying ancestries that derive primarily from the lineage leading to present-day Europeans are:
  - Kostenki 14 (from 37 ka, with uncertain archaeological association from western Russia)
    - contributed to the later Věstonice genetic cluster (hereafter, Věstonice cluster or ancestry), named after the Dolní Věstonice site in Czechia
    - this genetic signature is shared among individuals associated with the archaeologically defined Gravettian culture (33–26 ka) in central and southern Europe and seemingly disappeared after the Last Glacial Maximum (LGM)
  - Goyet Q116-1 (35 ka, Aurignacian-associated from Belgium)
    - After the LGM, a genetic component distantly linked to the Goyet Q116-1 individual from Belgium dated to 35 ka—named GoyetQ2 ancestry (hereafter, GoyetQ2 cluster or ancestry)—reappeared in individuals from southwestern and central Europe associated with the Magdalenian culture (19–14 ka from Iberia to eastern Europe across central Europe) and in an admixed form in subsequent Final Palaeolithic and Mesolithic hunter-gatherers, but the geographic extension of this ancestry is still unclear
  - Bacho Kiro 1653 (35 ka, probably Aurignacian-associated from Bulgaria)
Gravettians
- individuals associated with the Gravettian culture across Europe were not a biologically homogeneous population, culturally, however, we see both widespread general tendencies, such as weaponry and some portable art, and other aspects that have a more regional character, such as mortuary practices, various originalities in lithic and hard organic materials tool kits and adornments
- The ancestry found in individuals associated with the Aurignacian culture from central Europe (GoyetQ116-1 ancestry) gave rise to Gravettian-associated individuals from western and southwestern Europe. This derived ancestry—the Fournol cluster—survived during the LGM in Solutrean-associated individuals, possibly within the Franco-Cantabrian climatic refugium, leading to later populations associated with the Magdalenian culture (GoyetQ2 cluster and El Mirón)
- the ancestry found in pre-30 ka eastern European individuals (Kostenki cluster and Sunghir group) contributed to Gravettian-associated individuals from central and southern Europe (Věstonice cluster), the latter without descendants retrieved in post-LGM populations from those regions
- a genetic ancestry profile in individuals associated with Upper Palaeolithic Gravettian assemblages from western Europe that is distinct from contemporaneous groups related to this archaeological culture in central and southern Europe, but resembles that of preceding individuals associated with the Aurignacian culture.
Last Glacial Maximum LGM (25,000 to 19,000 years ago)
- is considered to have caused a demographic decline in large parts of Europe with populations retracting to southern latitudes as attested—for example—by the contemporaneity of the Solutrean culture (24–19 ka) in the Iberian peninsula and southern France.
  - Other proposed climatic refugia for human survival during this period are the Italian peninsula, the Balkans and the southeastern European Plain, but the actual genetic contribution of populations from these regions to post-LGM Europeans is highly debated
- Epigravettians
  - a genetic turnover in southern Europe suggesting a local replacement of human groups around the time of the Last Glacial Maximum, accompanied by a north-to-south dispersal of populations associated with the Epigravettian culture.
  - the ancestry of individuals associated with the Epigravettian culture (Villabruna cluster), which was found to genetically connect European and Near Eastern hunter-gatherers, reached southern Europe well before the transition between the Early and Late Epigravettian and possibly as early as the Gravettian–Epigravettian transition.
  - A phylogeographic reconstruction of different lineages carrying this ancestry further suggests its entry point into northeastern Italy from the Balkans followed by a north-to-south expansion into the Italian peninsula alongside a population decline through sequential bottlenecks.
  - in southern Europe, a distinct hunter-gatherer genetic profile was found as early as 17 ka in individuals associated with the Epigravettian culture (24–12 ka, from the Italian peninsula to the southeastern European Plain across the Balkans). This ‘Villabruna’ ancestry (hereafter, Villabruna cluster or ancestry) showed connections to ancient and present-day Near Eastern populations, but the mode and tempo of its expansion into the Italian peninsula remain unexplored. The Villabruna ancestry later appeared in central Europe and it is thought to have largely replaced groups related to the GoyetQ2 ancestry
- Magdalenians
  - Magdalenian-associated individuals not only from Iberia but also from the rest of Europe carry Epigravettian-associated ancestry (Villabruna cluster).
  - Genetic analyses of western European individuals associated with the preceding Badegoulian culture might provide clues on the processes that led to the formation of the GoyetQ2 cluster. As inferred from the archaeological record, the spread of the Magdalenian across Europe is linked to southwestern to northern and northeastern post-LGM population expansions and not to movements from southeastern refugia
- large-scale genetic turnover as early as 14 ka in central and western European hunter-gatherers
  - From at least 14,000 years ago, an ancestry related to the Epigravettians culture spread from the south across the rest of Europe, largely replacing the Magdalenian-associated gene pool.
  - This turnover is associated with multiple techno-complexes—Federmesser, Azilian and other Final Palaeolithic groups —despite considerable technological continuity with the preceding late Magdalenian
  - This broadly distributed ancestry (the Oberkassel cluster (also known as WHG)) is most closely related to an Epigravettian-associated individual from northwestern Italy, suggesting that its expansion into continental Europe might have started from the west—and not the east—side of the Alps. Moreover, the almost complete genetic replacement of the Magdalenian-associated gene pool raises the hypothesis that parts of Europe were differentially populated during the abrupt climatic variation starting around 14.7 ka with the Bølling–Allerød warming period, creating areas where southern European populations could expand. This might also explain the genetic uniformity of the Oberkassel cluster across large parts of western Eurasia but genomic data from between 15 and 14 ka is needed to understand the exact dynamics of this turnover.
- Oberkassel and Sidelkino ancestries
  - the Oberkassel ancestry in western and central Europe and the Sidelkino ancestry in eastern Europe remained largely isolated for almost 6,000 years until genetic interactions were first observed—around 8 ka in northeastern Germany, possibly associated with cultural exchanges along the Baltics and around 7.5 ka in the upper Volga region, possibly linked to the spread of pottery in the region
- After a period of limited admixture that spanned the beginning of the Mesolithic, genetic interactions between western and eastern European hunter-gatherers have been found, who were also characterized by marked differences in phenotypically relevant variants.⁷⁾

Paleoneurology

the cost of evolving the hominid brain

an opposable thumb is a feature of primates which allows them to climb tree branches better, but hominids took this much further to evolve a fully opposable thumb with far more functionality
but it is really the brain combined with bipedal gait to make the most use of this thumb that sets humans most apart from other species and the modern brain requires 20% of our blood supply and energy
as the brain evolved larger and larger (modern brain is 3x the size of chimpanzees which is already larger than most other species in relation to body weight), these energy requirements were met any several ways and with a number of ramifications
primates had evolved as hind gut fermenters and had diets consisting mainly of “C3” vegetation such as foliage from which they extracted the needed protein and energy by having to grind away eating for 50% of their waking hours and thus they had large molars and massive chewing muscles (masseters).
- in contrast, bovine animals were fore-gut fermenters and mainly ate “C4” vegetation such as grasses which has a different C12 :C13 ratio than C3 vegetation due to different enzyme systems used to process carbon.
primates supplement with fruits in season but these whilst providing energy do not provide protein or fats and sometimes supplemented with raw meats (small primates ate insects for protein but this is inadequate for large primates)
this raw vegetation and even raw meat was not sufficient to provide the energy and oxygen demands of the enlarging brain
- even now for adult women, if their diet was solely raw foods even if they included raw meat, the poor energy bioavailability of uncooked foods results in low BMI and 50% will have amenorrhoea - clearly this diet is NOT conducive to evolution if the species can't procreate efficiently
at some point they would have discovered distal limb bone marrow and the brain were relatively safe to eat as not only did these have a higher fat content, but were less accessible to bacteria after death
a key enabler for the early hominids was getting control of fire to cook, create smoke to given them access to honey, and to keep them warm at night. This was supplemented by the use of stone tools from as early as 3.3 million years ago thanks to early hands capable of limited throwing and clubbing, which perhaps drove evolution of the fully opposable thumb (perhaps 1mya with H. habilis and H.erectus) which then allowed powerful capability to throw objects and use clubs which were useful for hunting - by 500,000yrs ago, they had developed spears
cooking foods increased bioavailability of energy by about 50% and markedly reduced the need for fermentative hind gut as less foods were passed undigested, this allowed the hind gut to be reduced in size and divert its blood flow to the brain, further allowing the brain to evolve in size.
cooked foods meant that they needed to spend FAR less time chewing and eating and thus had far greater time to develop brain creativity and consider other activities
critically, the ability to cook meant that meat could be rendered far safer to eat if it was starting to decay, less chance of acquiring an helminth infection, and no longer did they need to rely upon bone marrow alone or early kills
red meat also was a far more effective source of iron which was increasingly critical for delivering oxygen to the brain as well as providing important nutrients such as critical unsaturated fatty acids which hominids can't synthesize for brain development and vitamins such as B12 which is essential for nerve development and functioning.
the growing increased emphasis on meat drove them to become game hunters and various features needed to occur to enable this:
- bipedal gait allowing hands free to attack game
- ability to run and tolerate the hot African conditions compounded by an increasing hot brain needing cooling (the larger brain essentially became a 20W heater enclosed in bone) required losing their fur (the fur was no longer needed for warmth now that they could make fires to keep them warm at night) and evolving naked skin which could perspire, but this unprotected skin needed to also evolve deep melanin pigmentation to protect from UV radiation and increasing blood circulation to dissipate the heat from the brain as well as provide glucose and oxygen in high quantities (hence larger carotid arteries entering the skull).
  - those species which migrated to regions with less UV evolved mechanism to either totally turn off melanin production to ensure vitamin D production (pale redheads), or to have a UV-responsive seasonal tanning capability (eg. olive skinned Mediterraneans)

Evolutionary changes of the cranium and brain size:

4 main evolutionary parts of the brain:
- pons, medulla & brainstem
  - the most primitive structures of the brain
  - these control autonomic functions such as breathing, heart functions & vital organ regulation
  - innate instincts:
    - 2 basic instincts which predate even Cambrian life forms and are DNA based:
      - self-preservation
        
        hunger
        
        thirst
        
        fear of predators esp. spiders/reptiles/dinosaurs
      - reproduction
- the R-complex
  - evolved about 350 million yrs ago
  - “Reptilian” but is actually originates from the early amphibians of the Devonian Period, & only later developed independently in reptiles, dinosaurs & mammals
  - an extremely important development in that it allowed rudimentary intelligence & problem solving capability
  - the basics of emotion developed along with the chemistry of instinct:
    - 3 abstract innate instincts that require a brain & hence evolved later than the above 2:
      - territorialism - fear of closed spaces - loss of territory
      - social hierarchy
      - ritualism
- limbic system:
  - about 65 million yrs ago, at the end of the Cretaceous Period when dinosaurs and reptiles dominated, the small mammals developed the limbic system which contained most emotions & was pre-wired with basic instinct information beyond what DNA can supply elaborating on the innate instincts:
    - self-preservation:
      - fear of falling - when primates started climbing trees
    - reproduction:
      - fear of mating rejection
- neocortex:
  - finally the 3rd, & most important development was the neocortex which is the seat of intelligence, human initiative & self awareness.
  - the growth of the right side of the brain before the left is purely accidental & accompanied the evolution of higher mammals, esp. primates including man
  - this allowed logic to over-ride immediate gratification of innate instincts
further brain developments:
- development of increased frequencies of skull emissary foramina from in A. africanus to Homo sapiens to allow intracranial veins to communicate with extracranial veins and thus provide for a radiator control system to prevent over-heating of the brain in hot environments and on exertion which allowed the brain to increase in size beyond its previous thermal constraints.
- rearrangement of vascular system to brain to compensate for bipedal stature's gravitational effects in A. africanus
- brain size increased 3-fold from the modern chimpanzee sized brain of the bipedal australopithecine 2 million yrs ago to the modern Homo sapiens
- the volume of the neocortex is linearly proportional to the total brain volume and thus is relatively constant proportion for all anthropoid primates
- relative volume of white matter increases with brain size from 9% in pygmy marmosets to 34% in humans
- brain weight in relation to body weight of various species:
the shrinking Y-chromosome:
- the current human Y chromosome consists of 45 genes, down from 1438 genes 300 million years ago
- the loss of the Y chromosome in many species has led to their extinction
- it is estimated that humans will lose the Y chromosome in 10 million years at the current rate.
- human fertility will decay to 1% of its present level in 125,000yrs

modern day micro-evolution

prevalence of the presence of a persistent median artery in forearms into adulthood (this normally regresses in early fetal periods after 8wks gestation) appears to have tripled in those of European descent over the past 100 years
prevalence of the fabella in the knee joint has tripled over the past 100 yrs
reducing prevalence of wisdom teeth

¹⁾

http://www.chron.com/news/science-environment/article/Scientists-recreate-oldest-human-ancestor-and-10900313.php

²⁾

http://www.xinhuanet.com/english/2020-04/03/c_138943482.htm

³⁾

http://science.sciencemag.org/content/361/6401/511

⁴⁾

Science Sept 2020

⁵⁾

Nature 2019

⁶⁾

https://www.nature.com/articles/s41598-021-83978-4