Evolution of Humans
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:
- 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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