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history:ev_human

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)
                                                      • 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) - 25-30mya
          • hominidae (Great Apes)
            • forest-dwelling apes
              • hunting apes (~15m yrs ago)
                • ? 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)
                  • hominids - ~5-7mya (split from chimpanzees)
                    • 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.
        • 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)
                • 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
  • 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 ago4), 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

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
history/ev_human.txt · Last modified: 2020/04/03 19:45 by gary1