we have more neurons in our cerebral cortex than other mammals. Our cortices are denser than elephants.
Orangutans/gorillas have 9 billion cortical neurons. humans have 16 billion neurons in our cortex...more than any other species. so, its not the size of our brain but the structure that is so remarkable.

sustained pair bonding
improves reproductive success
by enhancing coordination and cooperation between pair members. 

evolutionary adaptations

                   4. sexual dimorphism:
a. ​decrease in size of male canines/brow ridges
b. subQ body fat distribution
c. hair quantity/distribution
d. "hidden estrus"
      12 month fertility with no external signs
e. 15% size difference

“0pposable” = the thumb can be placed opposite the other fingers on the same hand, and touch each of them. Almost all primates have opposable thumbs, as do arboreal frogs, pandas and koala bears.
but humans have "fully opposable" thumbs so can can reach their thumb farther across our palms allowing for more accurate fine motor skills.. 

non-African humans have 1.5-2.6% Neanderthal DNA
Some Melansians have 4-6% Denisovan DNA 
A 40,000 ya skeleton in Romania showed 11% Neanderthal DNA = 5 generation past interbreeding.  

when Homo sapiens emerged 200,000 years ago, our brain had reached 1,300 grams from the 350 grams of our hominin ancestors. In 3 million years, primate brains quadrupled from the previous 60 million years of primate evolution.

chimp = Pan troglodyte

accommodations to the shift in the center of gravity included:
a. skull modification to foramen magnum
b. femur/ increase length and weight   

thrifty gene hypothesis suggests certain populations may have genes that permit increased fat storage which offerred a survival advantage dyrung famine but in a modern environment result in obesity and type 2 diabetes. 

Hair is unique to mammals.
It provides insulation and protection.
It permits social displays to indicate aggression or agitation.
The transition to bipedalism would have coincided with a change in lifestyle due to environmental changes (dry/hot) and diet.
So the transition to naked skin and an increase in sweat glands occurred 1.6 million years ago theoretically to offset greater heat loads.

the increase in thumb dexterity about 2 million years ago has been linked to the gradual development of complex culture and the
the appearance of the larger brains and that around the same time, humans gradually began to exploit animal resources and to rely more heavily on stone tool technologies, allowing
humans to take advantage of new dietary resources previously unavailable. 

NOTCH2NL
 NOTCH2NL genes influence an intercellular signaling system that plays a key role in neurogenesis by controlling human cortical stem cells.
​These stem cells divide to produce cortical neurons.

Although Homo erectus had a larger brain, and Homo neanderthalus had largest brain capacity, Homo sapiens displays neuron rich pre-frontal /temporal cortices strengthening decision making, social/behavioral skills, language.  and cognition.

LCA for chimps/humans was
Sahelanthropus tchadensis
6.5 mya  

transcription factor Engrailed 1 (En1) promotes the sweat gland prodution

Neanderthals and modern humans had
similar levels of manual dexterity
suggesting it was inherited from a common ancestor.

and the whole shebang...

​5. decrease in olfaction
AND increase in vision
Humans have the same number of genes (1000) for smell detection as other primates but
over half no longer function due to a mutation that prevents them from working properly.
As human brains development, a greater emphasis was placed on vision. 

3. ulnar oppostition = 
the opposable thumb
Opposable thumbs evolved about 2.6 million years ago coinciding with the frequent use of permitting stone tools.
First seen in genus Homo including Neanderthals
allowed for a precision grip, manipulation,
tool manufacturing/use. 

Genus Homo exhibits 3 additional hand muscles to chimps.

Homo sapiens closest ancestor = Homo erectus
(upright man) lived 1./9mya - 135,000mya
Homo habilus (nandy man) 2.4mya-1.4mya
Fossil evidence was first collected in 1856 in Neanderthal valley but dismissed as deformed Human.
In the 1920's, the start of collections of intermediate species began.
Africa was recognized as the seat of humanity in 1980s.
New discoveries as recently as 2015 in the Gauteng province of Africa of contemporaries of Homo sapiens.
15 skeletons unearthed that were intentionally buried.
Tentatively identified as Homo naledi.
The journey continues...!   

and should we consider this??

8. skull changes:
change in teeth alignment
loss of ocular ridges
emergence of a chin
emergence of a styloid process = muscle attachment for tongue and larynx

human dispersal:
Out of Africa Model =
a single wave of Homo sapiens migration occurred 100,00-65,000ya 
Homo sapiens speciated in Africa (Botswana) 200,000ya.
Homo sapien populations left Africa 100,000 ya, migrating throughout Eurasia, outcompeting existing Homo species already present from previous migrations of Homo erectus and Homo Heidelbergus. mDNA analysis supports this model over the Multiregional Model. 

evolution of bipedalism occurs so...
forelimbs free to use/carry tools and infants (but why hair loss), hunting, changes in habitat from jungle to savanna.

Early primates descended from small, nocturnal, insectivorous mammals. Today's tree shrew is the closest living relative to early primates and serves as a model
for what our predecessors might have been like. Early arboreal primates were adapted for life as tree dwellers. Prehensile hands and forward placed eyes permitting depth perception were advantages for life in the trees. 

How does NOTCH2NL works to boost neuron formation? The  NOTCH2NL protein blocks the
signaling pathway that causes stem cells to differentiate and stop dividing.
As a results, stem cells keep dividing, ultimately producing more neurons.  
If the NOTCH2NL gene is deleted from human stem cells in the lab, the stem cells differentiated faster into neurons, depleting the stem cell pool
and producing less cortex tissue.

2. bipedalism
evolved 6-7 mya
   chimps and gorillas are knuckle walkers
   Ardipithecus were fully bipedal 5.6 mya

The point in our evolutionary past when the branch of human lineage diverged from the one that produced the chimpanzees
and bonobos occurred in Africa 6.5  million years ago.

 Australopithecus afarensis (Lucy) may have been pair bonded. 
Pair-bonded animals usually exhibit similar body sizes and similar teeth. But A. afarensis is unique since they exhibit a large body size difference really similar teeth. Paleoanthropologists hypothesize that A. afarensis was either shifting towards being pair-bonded or completely pair-bonded but retained size differences for mate competition or protection from predators.

And although glucose is the brain’s first choice for energy, creatine provides back up energy when glucose levels are  low.
Creatine is ferried in and out of cells with the help of several genes.
When the expression levels of these genes were measured in tissue samples from humans, chimps and macaques, they found that human brains had twice the levels of the products of two creatine regulating genes called SLC6A8 and CKB. When the same levels were measured in human muscles,
the levels were the same as found in chimps.

The "modern" hand also coincides with Homo sapiens dispersal Out of Africa.

Homo sapien evolution

obligate bipedalism:
Australopithecus
fossils 4.2 -3.9 myo

and there's also this...
glucose is ​brain food. glucose is pumped into neurons via glucose transporters (Glut1)
which are encoded by
glucose transporter gene SLC2A1.
The DNA sequences of these genes exhibit
mutations in humans but not other primates.
 Compared with chimps, humans make 3X more neuron glucose transporter.
So in our brains, we have more GLUT1 protein moving more glucose from the bloodstream into the cerebrospinal fluid (CSF) surrounding
our brains. 
 Human's allocate 20-25% of our total resting metabolic rate to brain function. Yet our brains  make up just 2% of our body mass.
Non-human primates allocate 10% and other
mammals just 5%. 

Among primates, humans have 10X the  number of sweat glands compared to 
chimpanzees. The upregulation of the transcription factor Engrailed 1 (En1) promotes is correlated with increased sweat gland development in humans.
The product from an enhancer gene ECE18 upregulates En1 expression =
more sweat glands.

 Homo erectus originated in Africa and expanded to Eurasia about one million years ago. A second migration out of Africa happened about 100,000 years ago
by anatomically modern humans who conquered the world by completely replacing other Homo populations. 

c. knee/ankle joints increase strength
d. pelvis shorter and broader
   (which btw decreased birth canal size leading to shortened gestation (smaller heads) and longer alloparenting (K-selection) of immature juveniles.

7. loss of much body hair
AND 
increase in # sweat glands
we have 2-5 million sweath glands 

producing +/- 12 liters sweat/day.

Hominids include modern humans, and all our immediate ancestors including members of the genera Homo, 
Australopithecus, 
Paranthropus and 
​Ardipithecus.

 6. smaller gut =
more energy can be diverted from the intestines to the brain.
AND
faster metabolism
our accelerated metabolic rate results in more energy expenditure than even the great apes (820 kcal/day more!). 
We need more energy to support our larger and energy sapping brains. We also have a higher percentage of body fat compared to the other apes. Fat reserves protect increased energy demands.

1. increase in
brain function