What makes us Human?

common chimpanzee - Pan troglodytes is closest living relative to Homo sapiens sapiens       their DNA genomes are 99.5% identical -                 only 15 million of the 3 billion nucleotides have changed in 6 millions years,                 since the human and chimp lines diverged from a common ancestor.       Among these 15 million base changes lays the   DIFFERENCE  BETWEEN  HUMANS   &  CHIMPS       these changes helped survival & reproduction via positive selection and is what makes us HUMAN. Molecular Clock Dating - researchers by comparing the number of differences in their DNAs can      estimate when species diverged.  Recent efforts to identify those human genome regions that have      changed the most since chimps and humans diverged  from a  common ancestor      [circa 6 million years ago (mya)] have helped  pinpoint the DNA sequences that make us human.      Katherine Pollard (UCSF) has detailed these sequences changes between chimp and human DNA         genomes and discovered several rapidly evolving gene sequences that likely make us human.              top hit:  HAR1 - a stretch 118 bases.    Comparing the HAR1 DNA sequences between                                     chickens & chimps (lineage diverged 300 mya) shows differences in only 2 of 118 bases                                     yet humans differed by 18 bases from chimps [figure*].                                  HAR 1 function =   it codes for a regulatory RNA species and                                                       it is active in neurons that help develop the cerebral cortex.                                                                         malfunctions in HAR1  lead to abnormal foldings of cerebral cortex (lissencephaly)                                     thus HAR1 may have altered ancestral human brain function.               2nd:  HAR2 - a gene regulatory region that drives gene activity in the wrist and thumb during                                     fetal development whereas the chimp version cannot, thus favoring the dexterity to                                     manufacture complex tools.    Others*:  FOXP2 gene - is involved in speech.  Mutations in FOXP2 are unable to make subtle,                                     high-speed facial movement needed for normal human speech.                       ASPM - a gene linked to brain size;  mutations in ASPM result in microcephaly, in which                                     brain size is reduced by 70%.                       AMY1 - encodes salivary amylase & human have large number of the AMY1 gene, allowing                                     digestion of starch.                        LCT - gene for lactase. in most species only nursing infants can process lactose; but 9,000ya                                     human genome changes in Europeans & Africans produces an LCT version allow                                     adults to digest milk lactose from domesticated animals, while Asian & Latin                                     Americans are lactose intolerant.               Pollard's sequence analyses has identified 201 human accelerated gene sequences which are         regulatory regions that tell nearby genes when to turn on/off and more than half are located near         HAR genes and are involved in brain development.   back