Evolution

Evolution #

• Attempts to answer questions about our biological functions
• Is a theory — we don’t know for sure about the mechanisms, intricacies

Pre-evolutionary views (pre-Darwin) #

• Ancient India, Greece, China: earliest theories of evolution
• In Europe, predominant belief was stasis (fixed, unchanging)
• Ranking to order of life: the great chain of being
  • God > angels > humans > other animals…
• No other way to explain complexity other than God’s plan of creation

Scientific Revolution #

• Copernicus: earth not at center of universe
• Galileo: universe in motion (not fixed)
• Kepler, Descartes, Newton: laws of physics
• Age of discovery / Industrial Revolution: beginning of a new way of thinking

Classifying #

• John Ray: concept of a species and genus (similar groups of species)
• Carolus Linnaeus: book Systema Naturae
  • Adds class and order

Fossils #

• Many misconceptions early on, thought they were from Bible
• da Vinci, Robert Hooke, Nicholas Steno
  • Suggested that fossils were extinct animals
  • Sequence — top = young, bottom = old
  • Still used Bible to explain extinction (disasters caused)
• Cuvier: catastrophist; correlation of parts
• Buffon: changing environment; questioned catastrophism

Uniformitarianism #

• “Deep time” — time is immense and changing

Evolution before Charles Darwin #

• grandfather Erasmus Darwin: tried to explain complex life forms, and how they originated
• Jean Baptiste de Lamarck: forms could change/adapt based on changes in environment
  • thought adaptation was directional, approached perfection
  • “fluids”, “forces” caused changes, passed on to offspring — Inheritance of Acquired Characteristics
• Charles Lyell: incremental pace of geological change
• Thomas Malthus: demographer, examined population increase
  • natural forces would balance population growth
  • overproduction is contracted by nature
• Alfred Russel Wallace: natural selection, spiritualist

Charles Darwin #

• HMS Beagle, voyage around world to collect samples for natural history
• Galapagos islands: each island had similar animals, but slightly different features
  • Finches, tortoises, iguanas — differed on foods on islands
• Thought about selective breeding of flowers — get variations of life forms artificially
• Post-hoc selection: breeding relatives of offspring w/ favorable traits
  • parents are important also
  • reversal in logic: e.g. breeding for meat to get better meat
  • over lots of generations, favorable traits are more common
  • intentional selection
• Differential Reproduction: variation b/twn offspring; traits can be selected

Natural Selection #

Darwin’s Ingredients (1850s) #

1. “Grandchildren like grandfathers” — relatives share traits
2. Small, physical changes across generations; variations over time and over individuals
3. “great fertility in proportion to support of parents”: favorable traits help with survival of offspring

Richard Lewontin’s Ingredients (1978) #

basically reiterated Darwin

1. Heritability (genetics) — the same concept formalized for behavioral and clinical traits in 2-3 genetics, with the broader framing discussed in nature and nurture
2. Individual Variations (Recombination, degradation)
3. Overreproduction / biased reproduction

Evolution → Diversification ← #

• is a fact — backed by empirical evidence
• how it works (natural selection) is a theory

Misconceptions: #

• humans have stopped evolving because we can’t see any big changes

Misconceptions #

• humans have stopped evolving because we can’t see any big changes
• “survival of the fittest” means stronger, healthier…
  • Coined by Herbert Spencer
  • evolution changes based on the circumstances
  • which features get reproduced more than others?
  • fitness: differential reproductive success
• Progress fallacy: evolution is hierarchical, organisms evolve towards perfection
  • Reality: evolution has nothing to do w/ social progress
  • Not hierarchical — branches out in all directions
  • over time — more diverse + specialized, NOT better/complex
• Organisms get more complex due to evolution (evolutionary striving fallacy)
  • min. required complexity of life, so life inevitably goes towards complexity
• All evolution is by chance
  • current form/history affect how organism can change
• Species replacement fallacy
  • species only die out because of changes in environment, NOT because they replace other species
• Planet of the Apes fallacy: apes/other animals could ’take over’ the role of humans
  • Apes are highly evolved for their own niche

Trends in Selection #

▨ = dead

(time ↓)

• Stabilizing (most common) → result: less variation
• Directional → result: curve shifts
• Disruptive (dimorphic sexual traits, example: male vs female) → result: extremes are pulled apart

What Darwin Didn’t Know #

• Inheritability (genetics and inheritance)
  • Gregor Mendel: figured out combinatorial inheritance of traits (early research on genes — monogenomic traits)

Gregor Mendel #

Figured out combinatorial inheritance of traits (early research on genes – monogenomic traits)

Modern Genetics #

• Chromosomes are “supercoils” of DNA
• Thousands of genes in chromosome

Analogy #

• Base (ATCG) → Letter
• Codon (amino acid) → Word
• Gene (protein) → Sentence

Protein Synthesis #

• “Junk RNA” → 98% of DNA regulate gene functions, activity (like punctuation)
• Sequences can code up to 3 proteins
• RNA can turn on/off traits, discard genes