Hominidae Evolution Flashcards
hominidae
includes orangutans, gorillas, humans, bonobos, and chimpanzees
great apes/hominids
large body size
long arms, short legs, no tail
sexual dimorphism
-degree varies, typically males larger than females
omnivorous, most have preference fore fruit
large brains for body size
evolution of human lineage
estimates of chimpanzee and human MRCA range ~7 to 8 may
humans did not evolve from chimps, but rather from this common ancestor
lots of intermediate taxa that are now extinct
3 extinct genera
Ardipithecus (5-4 mya)
Australopithecus (4-2 mya)
Paranthropus (3-1 mya)
1 extant genus
homo (3 mya-present)
Ardipithecus (genus)
two extinct species that lived 4 to 5 mya
-fossils from Ethiopia
Grasping hallux (big toe) -adaptation for locomotion in trees
but hands more like modern humans than chimpanzees,
and pelvis also appears well suited for walking upright
brain slightly smaller than modern chimpanzee
reduced canines
-social structure with less aggression?
-chimpanzee males have relatively large canines and
high aggression between social groups
Australopithecus (genus)
7 to 9 extinct species that lived about 4 to 2 mya
fossils from eastern Africa
brain sizes ~35% the size of humans
high degree of sexual dimorphism (larger males)
teeth wear suggest mainly fruit diet, but also
vegetables and tubers
-fossil evidence of butchered animals near Australoptihecus
fossils also suggest meat consumption
Australopithecus afarensis
oldest member of genus; lived 3-4 mya
-“Lucy” fossil from Ethiopia
“Gracile” (slender) body type
about 3.5 to 5 feet tall
strong evidence of bipedialism
- shape of pelvis
- angle of femur
- attachment of muscles around knee
arboreal or terrestrial?
- curvature of fingers/toes adapted for grasping (arboreal)
- loss of grasping hallux (terrestrial)
Paranthropus robustus
lived 1.5 to 2 mya
“robust” body type
- strong upper body
- large skull with flare face and no forehead
- large brow ridges
- large herbivorous grinding teeth in mandible
most specimens have sagittal crest
-indicates strong jaw muscles
sagittal crest
indicates strong jaw muscles
1 extant genus: homo
7 or more species
-1 extant species = homo sapiens
genus is about 2.5-3 mya old
generally characterized by:
- long lower legs (walking and running)
- smaller teeth
- larger brains
bulge of Broca’s area (essential for speech) becomes visible
evidence of tool, fire, and burial of dead
Broca’s area
essential for speech
adaptation for bipedalism
foramen magnum more anterior
trunk
- S-curve of spine
- larger surfaces for muscles supporting upright posture
- expanded lumbar area
shortened forearms
pelvis and legs
- narrow pelvis
- femur angled toward midline
- long legs
feet
- all toes point forward
- enlarged heal and arch
bipedalism
bipedalism frees hands for carrying items, tool use
may be particularly beneficial in open habitats
-travel greater distances for food
overall trend of cooling temperatures in past 10 my
- partly dye to continental drift and changing ocean currents
- expansion of grasslands (particularly in Africa)
evolution of big brains
positive feedback between cultural/linguistic complexity technological advances, and diet
benefits
- store information
- quickly process information
- problem solving
- abstract ideas
costs
- lots of energy- your brain is 2% of body size but uses 20% of your energy
- more difficult childbirth
larger brain evolution may be linked to increased meat intake (energy)
biogeography history of Homo
oldest Homo species were in Africa
some species migrated out of Africa before the first H. sapiens
most notably:
- H. erectus in Asia
- H. neanderthalensis in Europe
so before Homo sapiens, there were homo species in Africa and Europe
fossil evidence of where homo sapiens originated
oldest H. sapiens fossils are all from Africa
-up to 195 mya
first H. sapiens fossils in other continents are 30-60,000 years old
molecular evidence of where homo sapiens originated
greatest extant genetic diversity in African population
-san people of souther southern Africa
populations outside of Africa have less diversity, consistent with:
- younger populations
- bottleneck during founder event
also evidence for introgression with other Homo species
evolution in modern Homo sapiens
whole genome data from >3000 UK citizens
examined genetic variation and tested for signatures of recent natural selection
higher points = detection of selection
LCT: lactase gene
MCH: major histocompatibility complex (immune system)
Lactose intolerance
most mammals only drink milk early in development while nursing
enzyme lactase is produced to break down lactose (sugar) in milk
lactase expression is reduced after weaning
-costly to produce when not needed (not drinking milk)
Lactase persistance
in Europe, humans started raising livestock 8-9000 years ago
- availability of milk for increased nutrition (advantageous)
- human niche construction
alleles that keep lactase general turned on past weaning were selected for because they provide higher fitness
evolution of lactase persistence
selection in UK population
Other traits under selection: – Pigmentation (-) – Height (+) – Infant head circumference (+) – Female hip size (+) – Fasting insulin (+) – Glycated hemoglobin (+) – … and others
UV radiation
UVB: – Damages skin surface, causes sunburns and some skin cancers – But also causes synthesis of vitamin D – Vitamin D needed for absorption of calcium
UVA: – Less intense than UVB, but causes skin damage – Breaks down folate – Deficiency of folate can lead to birth defects and decreased sperm production
distribution of UV radiation
near equator: high levels of UV radiation
-both types
also less seasonality
-changes during years
skin pigmentation
human ancestors Africa
-moved from forest to open, hot habitats
selection for cooling mechanisms
-more sweat glands and less hair
more skin exposure = selection for more melanin
- melanin protect form UVA, breakdown of folate
- since UVB levels are so high, vitamin D synthesis persists
migration to Europe = lower UV radiation
alleles that resulted in less pigmentation have higher fitness
-increased ability to make essential vitamin D
hypothesis that skin pigmentation is a balance between the pros (vitamin D production) and cons (folate breakdown) of UV radiation
primates
consists of two main groups: prosimians and anthropoids
prosimians
“before-monkey”
most living today are relatively small in size, reside in trees, and are active at night
includes lemurs, lorises, pottos, tarsiers
anthropoids
“human-like”
includes New World monkeys, Old World monkeys, gibbons, hominidae or great apes
hominins
a monophyletic group comprising the Homo sapiens and more than 20 extinct, bipedal relatives
braincase
the portion of the cranium that encloses the brain
it does not include the facial bones
Cro-Magnins
a population of Homo sapiens who were accomplished painters and sculptors and who buried their dead in carefully prepared graves
Neanderthals
another recent Homo species
made art and buried their dead in a ceremonial fashion
out-of-Africa hypothesis
the reading hypothesis for the evolution of Homo sapiens
contents that Homo sapiens evolved its distinctive traits in Africa and then dispersed throughout the world
it claims that Homo sapiens evolved independently of the earlier European and Asian species of Homo–meaning that there was no interbreeding between Homo sapiens and Neanderthals, Homo erectus, or Homo floresiensis
