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BIO342 L2

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Marc Johnson

BIO342 Lecture 2: Evidence for Evolution and Origins of Life Definitions Educational Goals  define "decent with modification" and “phylogeny”  recognize how fossils contribute to our understanding of evolution  homology and its evolution and interpretation  understand the hypothesis for the evolution of early life Recall from class 1  Evolution is a change in the frequency of an allele or genotype through time within a population ◦ frequency - population at single locus, two copies of allele, A and B ▪ varies from 0 to 1, if both start at being 0.5, both equally common, A increase to 1, then B would decrease to 0 because added up together must equal 1  Phenotypic evolution occurs when a change in the frequency of alleles or genotypes cause a change in the distribution of phenotypic traits within a population Descent with modification  All organisms present or past are descended from a single common ancestor. During this time lineages have genetically and phenotypically changed and split to form many branches.  This is the concept of: descent of modification Tree of life and phylogenies The Tree of Life  single lineage, split to more lineage, some went extinct, some continue to present day to have diversity today Tree of life = Phylogeny  a phylogeny is a representation of the history of descent and thus common ancestry ◦ relationships between organisms ◦ node - single population over 100 millions of years - diversified and split Evidence for evolution What is the evidence that organisms evolve and diversify?  2 forms of evidence: ◦ pattern based evidence: fingerprints of evolution that have been left through time ◦ direct evidence (watch it happen) Where did birds come from and how did they evolve?  common: all have feathers and wishbone - support for ribcage for flight, does not collapse on them Paleontology  Paleontology is the study of ancient organisms preserved in the fossil record  like time travellers Paleontological time travel: 318 mya  no birds, no mammals, no crocodiles, some fish  land ferns  hylonomus, partially aquatic Paleontological time travel: 235 mya  more diversity of plants  more diversity, -poids  beipiaosaurus ◦ anatomically identical to feathers ◦ bone almost like wishbone Paleontological time travel: 145 mya  dinosaurs  flying, wishbone, feathers, like a bird Today  10 000 types birds, all with feathers and wishbone What conclusion can we draw from these data?  The original organisms we saw in the early fossil record are now extinct (likely), or exst and undiscovered (unlikely but not impossible)  Ancient feathered dinosaurs evolved through time and gave rise to modern birds ◦ Only organisms that have feathers and wishbone are birds ◦ stands to reason - feathers on those organisms - shared common ancestor - lineages that might have given rise to them  Birds are the living descendants of dinosaurs. Birds are dinosaurs. Fossils  travel through time by looking at impression of remains on stone through time  shores of New Brunswick, tail drag and foot prints - hylomonus  beipiaosaurus 235 - with preserved feathers  archaeopteryx 145, wings and tail  inference of patterns through time  traits that are homologous Strengths and weaknesses of paleontology  The fossil record is the collection of all known fossils: ◦ provides snapshots through time ◦ allows us to infer evolutionary change and diversification  Weaknesses  the fossil record is not continuous (large gaps)  soft tissues rarely preserved ◦ i.e. T-rex might h
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