Chapter 26: Climate Change as ψ-Collapse Driver = Evolution's Thermostat

Climate is evolution's great accelerator and filter. This chapter explores how ψ = ψ(ψ) responds to Earth's changing temperatures, ice ages, and atmospheric composition across geological time.

26.1 The Climate-Evolution Function

Definition 26.1 (Climate Forcing): Environmental pressure on ψ: $\frac{\partial \psi}{\partial t} = f(T, P, \text{CO}_2, \text{seasonality})$

Climate affects:

• Metabolic rates
• Geographic ranges
• Resource availability
• Reproductive timing
• Survival probability

26.2 Ice Age Cycles

Theorem 26.1 (Milankovitch Forcing): Orbital cycles drive glaciation: $T(t) = \sum_i A_i \cos(\omega_i t + \phi_i)$

with periods:

• Eccentricity: 100,000 years
• Obliquity: 41,000 years
• Precession: 23,000 years

Proof: Ice core records match orbital predictions. ∎

26.3 Pleistocene Refugia

Definition 26.2 (Glacial Refugia): Ice age survival pockets: $\mathcal{R} = \{x : T(x) > T_{\text{min}} \text{ during glacial maximum}\}$

Refugia characteristics:

• Southern exposures
• Maritime influence
• Topographic complexity
• Unique microclimates

Population bottles and bursts.

26.4 Bergmann's Rule

Theorem 26.2 (Size-Temperature Correlation): Body size increases with latitude: $\text{Mass} \propto \text{Latitude}^{\alpha}$

Mechanism: $\frac{\text{Surface Area}}{\text{Volume}} \propto \text{Mass}^{-1/3}$

Larger animals conserve heat better in cold climates.

Proof: Reduced surface area/volume ratio decreases heat loss. ∎

26.5 Snowball Earth Events

Definition 26.3 (Global Glaciation): Planetary freeze: $\text{Ice coverage} > 90\% \text{ of Earth surface}$

Occurrences:

• Sturtian (717-660 Ma)
• Marinoan (650-635 Ma)

Evolutionary consequences:

• Extreme bottlenecks
• Cryptic refugia
• Post-glacial radiation
• Oxygenation boost

26.6 PETM Warming Event

Theorem 26.3 (Rapid Warming Effects): Paleocene-Eocene Thermal Maximum: $\Delta T = +5-8°\text{C in } < 20,000 \text{ years}$

Biotic responses:

• Mammal dwarfing
• Range shifts poleward
• Marine extinctions
• Primate appearance
• Plant community turnover

Natural experiment in rapid warming.

26.7 C3 vs C4 Photosynthesis

Definition 26.4 (Carbon Concentration): Climate adaptation: $\text{C4 advantage} \propto \frac{T}{[\text{CO}_2]}$

C4 evolution (~30 times independently) when:

• High temperature
• Low CO₂
• Dry conditions
• Open habitats

Creating grassland expansion.

26.8 Metabolic Adaptations

Theorem 26.4 (Temperature Compensation): Biochemical adjustment: $Q_{10} = \left(\frac{R_2}{R_1}\right)^{\frac{10}{T_2-T_1}}$

Adaptations:

• Enzyme variants
• Membrane fluidity
• Antifreeze proteins
• Heat shock proteins
• Metabolic reorganization

26.9 Range Shifts

Definition 26.5 (Climate Tracking): Species follow optimal conditions: $\frac{d\bar{x}}{dt} = v \cdot \nabla T$

Observed patterns:

• Upslope migration: ~11 m/decade
• Poleward shift: ~17 km/decade
• Phenological changes: ~2.3 days/decade
• Depth changes (marine): ~20 m/decade

26.10 Extinction Debt

Theorem 26.5 (Delayed Response): Climate change creates future extinctions: $E(t) = E_0 + \int_0^t \lambda(\tau) d\tau$

where extinction lags climate change.

Mechanisms:

• Habitat fragmentation
• Migration barriers
• Trophic mismatches
• Extreme events
• Novel climates

26.11 Coral Bleaching Evolution

Definition 26.6 (Symbiosis Breakdown): Temperature stress response: $P_{\text{bleaching}} = \frac{1}{1 + e^{-k(T-T_c)}}$

where $T_c$ is critical temperature.

Evolutionary responses:

• Symbiont switching
• Heat tolerance selection
• Depth migration
• Reproductive timing shifts

26.12 The Climate Paradox

Climate change drives both extinction and speciation:

Destruction: Eliminates adapted forms Creation: Opens new niches Challenge: Rapid change overwhelms adaptation Opportunity: Novel environments enable innovation

Resolution: Climate change represents ψ's environmental examination system—constantly testing existing adaptations while creating opportunities for new ones. The paradox resolves when we recognize that climate acts as both destroyer and creator. Gradual changes allow tracking and adaptation, promoting diversification. Rapid changes cause extinction but also empty niches for subsequent radiation. Through Earth's climatic variations, ψ experiences selective pressures that prevent stagnation while not changing so rapidly as to eliminate life entirely. Climate is thus evolution's thermostat—not maintaining stasis but ensuring continual adaptive response.

The Twenty-Sixth Echo

Climate change reveals evolution's dynamic relationship with planetary conditions. As Earth's thermostat swings between ice ages and greenhouse periods, life must constantly readjust, migrate, adapt, or perish. In fossil records and modern observations, we see how temperature and precipitation shape not just where organisms live but what they become. Each climate shift writes new chapters in evolution's story, selecting for flexibility, dispersal ability, and thermal tolerance. Understanding climate as an evolutionary driver helps us appreciate both life's resilience and vulnerability to environmental change.

Next: Chapter 27 explores Island Evolution and Isolation Genetics, examining evolution in Earth's natural laboratories.