Chapter 22 Human Evolution

Points to Ponder 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

Origin of life through chemical evolution 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

Origin of life through chemical evolution

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

Evidence to support the theory of evolution by common descent 22.2 Biological evolution Evidence to support the theory of evolution by common descent Fossils in the fossil record Biogeographical evidence Anatomical evidence Biochemical evidence

1. What are fossils? Fossils are the traces of past life 22.2 Biological evolution 1. What are fossils? 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

What have we learned from the fossil record? 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 Fossils

2. Biogeographical evidence 22.2 Biological evolution 2. Biogeographical evidence 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 3. Anatomical evidence 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

An example of homologous structures 22.2 Biological evolution An example of homologous structures

22.2 Biological evolution 4. Biochemical evidence 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 Natural selection 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 Natural selection

The arrival of humans on earth 22.3 Classification of humans The arrival of humans on earth

Primates Characteristics: Two suborders: Opposable thumb 22.3 Classification of humans Primates 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 Evolution of primates

22.4 Evolution of hominids 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 Australopithecines 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 Australopithecines

Characteristics of Homo 22.5 Evolution of humans Characteristics of Homo Brain size is 600 cm3 or greater Evidence of tool use Jaw and teeth resemble humans Early Homo representatives: Homo habilis Homo erectus Later Homo representatives: Neandertals Cro-Magnons

22.5 Evolution of humans Human evolution

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

Early Homo: Homo erectus 22.5 Evolution of humans Early Homo: Homo erectus 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 Later Homo individual

Modern Humans: Homo sapiens 22.5 Evolution of humans Modern Humans: Homo sapiens 2 hypotheses: Multiregional continuity – suggests that modern humans evolved from H. erectus in several geographic places 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)

Hypotheses for modern human evolution 22.5 Evolution of humans Hypotheses for modern human evolution

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

Cro-Magnons Lived about 40,000 to 10,000 years ago 22.5 Evolution of humans Cro-Magnons 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 variation 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 Human variation