Summary
Evolution Notes COMPLETE SUMMARY
- Institution
- University Of Cape Town (UCT)
Notes covering the evolution section of the BIO1004S course.
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Module 1: EvolutionCHAPTER 21 — EVOLUTION AND CHAPTER 22 — PHYLOGENETIC RECONSTRUCTION
EVOLUTION = descent with modi cation. + a change in the genetic composition of a population
from generation to generation
• Evolution = pattern + process
• Pattern = revealed via data across scienti c disciplines
• Process = mechanisms that produce the observed pattern of change
CONCEPT 21.1
SCALA NATURAE AND THE CLASSIFICATION OF SPECIES
• Aristotle —
• Viewed species as xed + unchanging
• Arranged life on a ladder of increasing complexity - Scala naturae
• Views each form of life as perfect and permanent
• Linnaeus —
• Developed binomial format for naming species
• Nested classi cation system
• Groups similar species into increasingly general categories
• Similar species w/in genus, similar genera w/in family etc
Species —> genus —> family —> order —> class —> phylum —> kingdom —> domain
IDEAS ABOUT CHANGE OVER TIME
• Fossils = remains or traces of organisms of the past
• Many found in sedimentary rocks
• New layers of sediment cover old ones and compress them into superimposed layers of
rock (Strata)
• Erosion may later reveal olde strata
• Cuvier —
• Observed changes in fossils of di erent rock strata
• Older stratum = more dissimilar fossils to current life-forms
• New species appear / disappear across strata — inferred extinctions occurred!
• Suspected each boundary between strata to be because of a catastrophic event (eg
ood)
• CATASTROPHISM = belief that there must have been successive catastrophes ( oods,
droughts etc) that wiped out most life forms
• Lyell —
• Promoted idea of uniformitarianism
• UNIFORMITARIANISM = belief that most geological features are caused by slow gradual
changes (eg. Earthquakes, volcanoes shape the earth)
• Stated that the laws of nature have been consistent over time (same processes in
operation at the same rate)
• Therefore… earth = old and change = gradual
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, LAMARCK’S HYPOTHESIS OF EVOLUTION
• Proposed a mechanism for how life changes over time
• Promoted gradualism
1) use and disuse principle
1) Parts of the body that are used extensively become larger and stronger, those that are
unused deteriorate
2) Eg. Gira e neck stretching
2) inheritance of acquired characteristics in response to the environment
1) organisms can pass on these modi cation onto o spring
- not in line with genetic theory!!
• Lamarck thought that evolution occurs because organisms have an innate drive to become
more complex — “complexity is achieved by will”
CONCEPT 21.2 DESCENT W/ MODIFICATION BY NATURAL SELECTION EXPLAINS
ADAPTATIONS
BY THE 19TH CENTURY..
• Accepted that the earths as in the range of millions of yrs old
• Acceptance of fossil record
• Similarities among di erent species noted
• Descended from previously existing organisms
THE VOYAGE OF THE BEAGLE
1831 —
• Darwin takes unpaid post on the H.M.S. Beagle w/ FitzRoy
• Mission is to chart poorly knowns stretches of the South American coastline
• Voyage around the world
• 5 years
• Collected a range of plants, insects, fossils
• Studied geological formations
• Found fossils similar to modern forms
• Eg. 3 toed sloths (tree living) and giant fossil sloths (ground-living)
• Observations reinforced learnings from Lyell
• Physical evidence did not support the traditional view that Earth was only a few thousand
years old
• Galapagos islands ndings
• 950 km o NW coast of South America
• Volcanic; no contact w/ mainland
• Islands are fairly close to each other
• Far from elsewhere
• Observed unusual organisms
• Darwin’s nches
• 1 species on the mainland but 14 on islands
• Diverse use of habitat
• Ancestor was probably a seed-crushing ground dweller
• Galapagos tortoises
• Each island was “inhabited by a di erent set of being”
• All di ered slightly from one island to the next
• Two main types based on shell-shape
• Saddle backed vs dome shaped
• Saddle = feeds on taller cacti
• Dome = feed on vegetation close to the ground
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, DARWIN HYPOTHESISED THAT THE GALAPAGOS HAD BEEN COLONISED BY ORGANISMS
THAT HAD STRAYED FROM S. AMERICA AND THEN DIVERSIFIED - GIVING RISE TO NEW
SPECIES ON THE VARIOUS ISLANDS
DARWIN’S FOCUS ON ADAPTATION
• ADAPTATIONS = inherited characteristics of organisms that enhance their survival and
reproduction in speci c environments
• Arise via NATURAL SELECTION = a process in which individuals have certain inherited traits
tend to survive and reproduce at higher rates than other individuals because of those traits
• Alfred Wallace developed a hypothesis almost identical to Darwin
IMPORTANT INFLUENCES FOR DARWIN WHEN FORMULATING HYPOTHESIS:
1. Diversity of life
1. Recognition of forms similar to what he knew but had adapted to the local environment
2. Adaptations
3. Fossils and extinct forms
• Eg. Glyptodonts and armadillos
4. Galapagos islands
• Concentration of biodiversity that led to an understanding of the changes
5. Widely distributed species often occur in di erent regions
6. Geology
• Earthquake in S. America during Beagle voyage
• Cape of Good Hope (Malmesbury rocks and molten granite)
• Andes Mountain fossils
• Darwin utilised a scienti c approach
• Induction
• Fact nding
• Synthesis
• Deduction
• Certain things should follow if the general statement is true
• Hypothesis testing
• Must be well de ned and falsi able
• Must be able to test validity
THE ORIGIN OF SPECIES
• Three broad observations about nature
• Unity of life
• Diversity of life
• Match between organisms and their environments
DESCENT W/ MODIFICATION
• Organisms share many characteristics — unity of life
• Must have all come from a common ancestor of the remote past
• Darwin viewed the history of life as a tree
• Multiple branchings o of a common trunk to the tips of twigs
• Reasoned that a branching process + extinction events explain morphological gaps between
related groups of organisms
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