Evolution of Humans

• Speculative family tree
• Paleoneurology
• see also:
  • Prehistoric times
  • Evolution of Human Sexuality
  • Ancient history

Speculative family tree:

• pre-humanoid ancestry:
  • primitive insectivore mammals
    • pre-monkeys - diet extended to fruit, nuts, leaves; eyes more anterior => 3D vision; manipulating limbs
      • New World monkeys - did not evolve to apes
      • Old World monkeys (25-35m yrs ago) - long, balancing tails; increasing body size; brachiating => arboreal;
        • 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
                • 1st hominids (~7m yrs ago) break away from chimpanzee evolutionary line in Africa
                  • 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
• Common human ancestor (Africa 5m yrs ago)
  • Ardipithecus ramidus (Ethiopia 4.4m yrs ago)
  • Australopithecus anamensis (Kenya 4.2m yrs ago)
    • 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;
        • H. rudolfensis (Eastern Africa 2m yrs ago)
        • 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 (Eastern Asia 1m-40,000 yrs ago)
            • H. floresiensis (Flores, Indonesia until 13,000 yrs ago ?until 16thC AD, disc. 2004) - small brain, 1m tall
            • H. antecessor (Spain 0.7m yrs ago)
              • H. heidelbergensis (throughout Old World 0.6m yrs ago)
                • H. neandertherthalensis (Europe & Western Asia 200,000-30,000 yrs ago)
                • H. sapiens (150,000/200,000 yrs ago in Africa;  40,000 yrs ago in Europe; to present) creativity; art; symbolic thought;language;
                  • oldest known H.sapiens c160,000BC in Ethiopia (disc. 1997)
                  • 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.
                  • 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

Paleoneurology

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
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