Human Evolution

• What is the chemical evolution of life?
• What is biological evolution?
• What is natural selection and what three elements are vital for this?
• What was Darwin’s contribution to evolution?
• What have we learned from the fossil record?
• Explain the fossil, biogeographical, anatomical and biochemical evidence that supports the theory of evolution by common descent?
• What are analogous, homologous and vestigial structures? Give examples of each.
• How are humans classified?
• What characteristics do primates have in common?
• Explain the evolution of hominids.
• Who is Lucy?
• Explain the evolution of humans.
• What are the 2 hypotheses for modern man?
• Compare and contrast Cro-Magnons and Neandertals

22.1 Origin of life
• Steps of chemical evolution :
– Gases of the primitive atmosphere formed small organic molecules
– Molecules combined to form macromolecules
– Only RNA might have been needed to form the first cells and is supported by the fact that RNA can act as enzymes called ribozymes (RNA-first hypothesis)
– Protocells made of proteins and lipids could metabolize by using oceanic organic molecules but could not reproduce
– The true cell can reproduce and has DNA as its genetic material

22.1 Origin of life

22.2 Biological evolution
• Biological evolution – change in population or species over time
• 2 important points:
1. Living things descended from a common ancestor and thus have common chemistry
2. Livings things adapt to their environment
• Adaptation – a characteristic that makes an organism to survive and reproduce in its environment

22.2 Biological evolution
1. Fossils in the fossil record
2. Biogeographical evidence
3. Anatomical evidence
4. Biochemical evidence

22.2 Biological evolution
• Fossils are the traces of past life
• Fossils allow us to trace the descent of a particular group
• Charles Darwin, an English naturalist, relied on fossils to formulate the theory of evolution
• Transitional fossils have characteristics of two different groups

22.2 Biological evolution
What have we learned from the fossil record?
• Fossil record tells us that life progressed from simple to more complex
• Prokaryotes are the first life forms seen in the fossil record followed by unicellular eukaryotes and then multicellular eukaryotes
• Fishes evolved before terrestrial plants and animals
• Nonflowering plants preceded flowering plants
• Amphibians preceded reptiles
• Dinosaurs are directly linked to birds

22.2 Biological evolution

22.2 Biological evolution
• Is the study of the distribution of plants and animals throughout the world
• Supports the hypothesis that organisms originate in one locale and then may spread out
• Different life forms are expected whenever geography separates them
• Islands demonstrate this because they have many unique life forms because of geographic isolation

22.2 Biological evolution
• Common descent hypothesis offers plausible explanation for anatomical similarities among living organisms
• Homologous structures – structures anatomically similar that are inherited by a common ancestor e.g. Vertebrate forelimbs
• Analogous structures – structures that serve the same function but they do not share a common ancestry and thus are not constructed the same e.g. Wings of a bird and wings of an insect
• Vestigial structures – anatomical features fully developed in one group but are reduced and may have not function in another group e.g. Whales have a vestigal pelvic girdle and legs

22.2 Biological evolution

22.2 Biological evolution
• Almost all living things use the same biochemicals (e.g. DNA and ATP)
• Living things use the same triplet code
• Living things use the same 20 amino acids in their proteins
• Living things share many of the same genes

22.2 Biological evolution
• A theory by Darwin that describes a mechanism by which a species becomes adapted to its environment
• 3 vital elements:
• Variation – there must be physical variations that can be passed from generation to generation
• Competition – there must be competition for limited resources (food, mates, shelter) and those better adapted will survive and reproduce
• Adaptation – subsequent generations will see an increase in individuals with the same adaptations as long as the environment remains unchanged

22.2 Biological evolution

22.3 Classification of humans

22.3 Classification of humans
• Characteristics :
• Opposable thumb
• Stereoscopic vision (depth perception)
• Well-developed brain
• Reduced # of offspring (usually a single birth) with an increased period of parental care
• Emphasis on learned behavior and social interactions
• Two suborders :
• Prosimians – includes lemurs, tarsiers and lorises
• Anthropoids – includes monkeys, apes and humans

22.4 Evolution of hominids

22.4 Evolution of hominids
• Hominids – human lineage on the evolutionary tree
• Characteristics :
• Bipedal
• Flatter face with more pronounced chin
• Brain size
• Suggested fossils of the first hominids (~ 6-7 MYA):
• Central African fossil ~7 MYA ( Sahelanthropus tchadensis )
• Eastern African fossil ~ 6 MYA ( Orrorin tugenensis)
• Eastern African fossil ~ 5.8-5.2 MYA ( Ardipithecus kadabba )
• Hominids split from the ape line of descent ~ 7 MYA

22.4 Evolution of hominids
• A group of hominids that evolved and diversified in
Africa ~ 3 MYA
• Some had slight frames and others were robust with massive jaws that fed on plant materials
• Walked upright
• Limbs proportions are ape-like
• Small brain
• Famous skeleton named “Lucy” is from this group
• Australopithecus africanus has a large brain is is the most likely ancestral candidate for early Homo

22.4 Evolution of hominids

22.5 Evolution of humans
1. Brain size is 600 cm 3 or greater
2. Evidence of tool use
3. Jaw and teeth resemble humans
Early Homo representatives:
• Homo habilis
• Homo erectus
Later Homo representatives:
• Neandertals
• Cro-Magnons

22.5 Evolution of humans

22.5 Evolution of humans
• Lived ~ 2.0-1.9 MYA
• Large brain with enlarged speech area
• Omnivorous (hunters and gatherers)
• Primitive tools
• Culture may have existed

22.5 Evolution of humans
• Lived ~ 1.9-0.3 MYA
• Larger brain than H. habilis
• Flat face with the nose projected
• Tall and stood erect
• Striding gait
• May have migrated from Africa to Europe and
Asia
• Advanced tools and fire (systematic hunters)
• Language may have evolved

22.5 Evolution of humans

22.5 Evolution of humans
• 2 hypotheses:
1.
Multiregional continuity – suggests that modern humans evolved from H. erectus in several geographic places
2.
Out-of-Africa hypothesis – modern humans evolved from H. erectus most likely only in
Africa and later migrated to Europe and Asia
(this hypothesis has the most support)

22.5 Evolution of humans
Hypotheses for modern human evolution

22.5 Evolution of humans
• Discovered in Germany
~2000 years ago
• Massive brow ridges
• Nose, jaws and teeth protrude forward
• Low and sloping forehead, no chin

22.5 Evolution of humans
• Lived about 40,000 to
10,000 years ago
• Oldest fossils to be designated Homo sapiens
• Modern appearance
• Advanced culture including art, tool and maybe language
• Good cooperative hunters

22.5 Evolution of humans
• Human variations between populations are called ethnicities
• Variations evolved as adaptation to local environments:
– Skin color: range of dark to light
– Body shape: Bergmann’s rule and Allen’s rule

22.5 Evolution of humans