Today is Charles Darwin's birthday (1809). He's an inspiration for his broad perspective and exposition of evolution, the core of biological thinking. Once I visited his home and strolled slowly on his sandwalk, his thinking path, my head down to avert distraction, hands clasped behind my back, hoping to connect. I thought about present-day arguments of gradual versus sporadic evolution and concluded that both occur. Fossil and modern observational and experimental evidence indicate convincingly that change usually is slow but tends to spurt across abrupt physical boundaries and especially when catastrophes redirect the play.

Furthermore, whether physical or biological factors are major operators between catastrophes is no either/or proposition in the inclusive Biosphere. Yet some argue about that too, and I don't understand why. Do we seek authority in exclusive explanations? It's clear to me that physical factors are more influential in climatically stressful situations such as species-poor desert and polar regions and early successional stages. Conversely, biodiversity's regulation through competition, predation, and other interactions prevails in the relatively benign tropics and older, species-rich, highly structured communities.