The Elements of Evolution – Patterns


Rapid evolution is clearly a reality over fairly short time periods, sometimes just a few generations. But those rapid changes do not always persist and may be confined to small populations. The long-term dynamics of evolution appear to be quite slow. ~ American evolutionary biologist Josef Uyeda

Adaptation appears a constant force. This may result in variation within populations or short-lived speciation. For evolutionary changes to become pronounced and prolonged, the provocative forces at work must persist at the habitat level. Such incentives include predation, habitat change, or other ecological disturbance, including mating preferences.

15 MYA fruit bats evolved a low, broad skull that allowed even a small bat to have the strong bite needed to eat hard fruits. The result was a burst of speciation to consuming more fruits. Meantime, adaptive change in skull shape slowed, as a near-optimal arrangement had already been achieved.

The idea of punctuated equilibria originated from observing rapid adaptive radiations that settled into stasis, as fruit bats illustrate. Such is only one evolutionary pattern; there are several others, as are illustrated throughout this book.

It has long been thought that dramatic changes in a habitat drive speciation. Instead, counterintuitively, prolonged periods of stability are more important.

The strongest predictors of speciation are the amount of time a lineage has persisted in the landscape and the ability to move through the landscape matrix. ~ American biologist Robb Brumfield & American ornithologist Brian Tilston Smith et al

The deeper one delves into the patterns of changes in Earth’s life forms, the more apparent it becomes that evolutionary transitions may be fast or slow, that adaptation may result in convergence or divergence, and that evolution may seem (in hindsight) predictable or inventive.

Nature is not embarrassed by difficulties of analysis. ~ French engineer and physicist Augustin Fresnel