Section 27.2 – Evidence of Evolution

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Biological evolution (evolution) is all the changes that have occurred in living things since the beginning of life Table 27.1 ◦ Earth is ~4.6 billion years old ◦ Prokaryotes (first living organisms) ~ 3.5 billion years ago ◦ Eukaryotic cells ~2.1 billion ◦ Multicellularity ~700 million years

Descent with modification - all living things share the same fundamental characteristics: ◦ Made of cells ◦ Take chemicals and energy from the environment ◦ Respond to external stimuli ◦ Reproduce Living things are diverse ◦ adapted to different environments Provide evidence that evolution occurred in the past and is still occurring

Fossil Evidence Fossils are the remains and traces of past life or any other direct evidence of past life Most fossils are found embedded in sedimentary rock ◦ Weathering + erosion of rocks = sediment ◦ Particles can accumulate = stratum (layer of rock)  Used to relative age fossils (depth/layer)

Fossil Evidence Fossils can serve as transitional links between groups ◦ Example: Archaeopteryx (lived ~165 million years ago), intermediate form between dinosaurs and birds ◦ Some traits are like descendants and some are similar to ancestors

Geological Timescale Studying strata, divide earth’s history into: ◦ eras – periods – epochs Two ways to age fossils ◦ Relative dating  Relative order of fossils and strata based on the layer of rock  Does not determine the actual date ◦ Absolute dating  Relies on radioactive dating to assign an actual date  All radioactive isotopes have a particular half-life  Carbon 14 ( 14 C) is the only radioactive isotope in organic matter

Biogeographical Evidence The study of the range and distribution of plants and animals in different places throughout the world ◦ 6 biogeographical regions Continental Drift ◦ Positions of continents and oceans have changed over time; ◦ Creates a barrier to accessibility ◦ Permian period ~250 million years ago ◦ Triassic period ~220 million years ago ◦ Jurassic period 144 million years ago ◦ Cretaceous period 65 million years ago ◦ Present day

Biogeographical Evidence Extinctions ◦ Extinction is the death of every member of a species Mass extinctions ◦ A large percentage of species become extinct within a relatively short period of time 5 major mass extinctions ◦ End of Ordovician, Devonian, Permian, Triassic, and Cretaceous

Biogeographical Evidence Reasons for mass extinctions??? Asteroid ◦ Cretaceous extinction was maybe due to an asteroid that exploded = meteorites Continental Drift ◦ Ordovician extinction  Gondwana arrived at the South Pole and froze ◦ Devonion  Gondwana moved back to the South Pole – marine extinction

Anatomical Evidence Anatomical similarities among organisms  Example: Vertebrate forelimbs - same sets of bones organized in similar ways but dissimilar functions Unity? ◦ Common Ancestor

Anatomical Evidence Homologous structures: anatomically similar (inherited from a common ancestor) ◦ Homology = organisms are related Analogous structures: same functions but not constructed similarly (no common ancestry) ◦ Wings of birds and bats Vestigial structures: features are fully developed in one group but are reduced/no function in similar groups ◦ Ex: Ostrich – has wings but does not fly

Anatomical Evidence Traces of evolutionary history! ◦ Ancestral history  Ex. Ambulocetus to whales (land to water) Relate homology to embryological development ◦ All vertebrates as embryos:  Postanal tail  Pair pharyngeal pouches  BUT develop differently:  Fishes and amphibian – functioning gills  Humans – cavity of the middle ear and auditory tube, tonsils, thymus and parathyroid glands

Biochemical Evidence Almost all living organisms use the same basic biochemical molecules ◦ DNA, ATP, enzymes ◦ Same DNA triplet code (20 amino acids - for proteins) Only slight differences ◦ Humans share a large number of genes with simpler organisms ◦ More similar DNA sequences – more similar the organisms are

Evolution is no longer just a hypothesis – but is a theory Theory? ◦ Conceptual schemes that are supported by a large number of observations and scientific experiences

SUMMARY EVOLUTION? ◦ all the changes that have occurred in living things since the beginning of life due to differential reproductive success 4 types of evidence? Examples? ◦ Fossil ◦ Biogeographical ◦ Anatomic ◦ Biochemical

Complete Check Your Progress p.548 #1-3 Complete Check Your Progress p.550 #1-2 Evidence of evolutionary change through time