Chapter 22: Understanding the Diversity of Living Things

linnean taxonomy

a series of nested categories that go from broad to specific

linnean taxonomy order

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

Binomial nomenclature

the system of giving all living things two names: genus + species

evolution

change in allele frequency within a population over generations 

Plato (Typological thinking)

believed every organism has a perfect, unchanging essence 

• variation = “shadows”, unimportant distractions from ideal form

Plato example

all pens share the “essence of pen”, differences are irrelevant

Aristotle (extended typological thinking)

• believed organisms are static (no change)

• supported spontaneous generation

spontaneous generation

life arises from non-living matter

Great Chain of Being (Scala Naturae)

life arranged hierarchically from “lower” to “higher”

fossil record 

shows life is not static

evidence of evolution

extinction, transitional forms, vestigial traits, geographic relationships, homology vs. analogy

transitional forms

link past + present species

vestigial traits

traits that once served a function but no longer do

transitional forms example

a tetrapod limb evolved from fish fins

vestigial trait examples

• goosebumps

• coccyx (vestigial tail) 

Geographic relationships

similar species cluster geographically because they descended from a shared common ancestor 

Geographical relationships example

Galapagos mockingbird: similar species in same region → common ancestry

Homology

similar due to common ancestry

genetic homology

genes or their encoded proteins, that share a common evolutionary origin from a single gene in a common ancestor

genetic homology example

there is a gene that dictates where the eye will form (Pax 6 gene shared between mice and flies)

developmental homology

the concept that structures in different species are similar because they derive form the same embryonic tissues or developmental pathways; indicating inheritance from a common ancestor

developmental homology example

embryos (chicken, cat, humans) share phylotypic stage features (hull patch)

Phylotypic stage

the point during embryonic development when embryos of related animal species look most alike, sharing a basic body plan that is highly conserved across the phylum but diverges in later stages

Structural homology

physical traits found in different species that have a similar underlying structure, suggesting they were inherited from a common ancestor, even though they have different functions

structural homology example

vertebrae limbs are built on the same basic plane

analogy

similarity through convergence (independent evolution)

Theories of evolution: Lamarck

• believed in evolution but still hierarchy; + progressive

• organisms spontaneously generated, then evolved “up the ladder”

• proposed inheritance of characteristics (wrong)

inheritance of acquired characteristics

traits gained during life passed to offspring (lifting weights=muscular children) → WRONG

Theories of evolution: Charles Darwin

• proposed theory of natural selection with Alfred Wallace

• observed Galapagos finches: variation in beaks shapes tied to diet/environment

• shifted from typological thinking → population thinking

  • variation is essential

theory of natural selection

explains how species change over time by favoring traits that increase an organisms chance of survival + reproduction

population thinking

emphasizes variation amongst individuals rather than fixed or ideal type

Darwins 4 Postulates (truths) of Natural Selection

1. Variation exists in populations

2. some traits are heritable

3. not all individuals reproduce equally

4. those that produce more offspring will make up more future generations

Did evolution occur through natural selection?

Yes

fitness

measured by how many offspring they leave behind

• survival is secondary

fitness example

Australian Redback Spider

• female spider is larger than male spider

• male sacrifices himself during mating (flips so female can eat him) (as a distraction) → to increase chance of reproduction

evolution in action: microorganisms → Tuberculosis + MRSA

• multi drug resistant (MDR) strains evolved after antibiotic use

• single mutation in RNA polymers→ resistance

• Resistant cells survive drug therapy + reproduce → populations evolve

constraints on natural selection: non-adaptive traits example

flamingos are pink because of pigments tin the shrimp they eat, not because the pink gives them a survival advantage

constraints on natural selection: genetic constraints

evolution can only work with existing genetic pathways 

constraints on natural selection: genetic constraints example

humans cannot evolve wings because the developmental pathway does not exist

constraints on natural selection: Fitness tradeoff

traits can improve one function while reducing another → energy and resources are limited

constraints on natural selection: fitness tradeoff example

big testes → more sperm production → increased reproductive success → energetically costly → small brain (“big testes” = “small brain”) (“small testes” = “big brain”)

constraints on natural selection: Historical Constraints 

evolution is limited by ancestry - new adaptations must be built on what came before 

constraints on natural selection: historical constraints example

giant insects had to shrink due to lack of oxygen to support their respiration system

Homologous structures

body parts in different species that are similar in structure due to shared ancestry

homologous structure example

human arm and bat wing, same bond structure, different functions

analogous structures

body parts in unrelated species that serve similar functions but evolved independently 

analogous structures example

butterfly and bird wing → same function, different evolutionary origins

Convergent evolution

process where distantly related species evolve similar traits due to similar environments or ecological pressures

Convergent evolution example

fins in dolphins and whales

divergent evolution

process where closely related species become increasingly different over time; often leads to speciation

divergent evolution example

Darwin’s finches developing different beak shapes

speciation

formation of new species