LIFE, TIME AND CHANGE

In the previous post I mentioned the Darwinian concept of evolution which widely disturbed the 19^th century mindset. Today I’d like to explore the idea a little bit more, and challenge it.  

In simple words, Darwin stated that organisms within the same species vary and that the offspring inherits a part of that variation. He believed that the individuals that are more compatible with their environment are more likely to survive and pass on their variants. Consequently, better-adapted traits accumulate and shape species through natural selection.

So according to Darwin’s idea (and related theories of gradualism), the processes of evolution are slow but continuous. This hypothesis also suggests that highly adapted, dominant species resist novel change, which means that if a significant environmental alteration occurs, dominant species might simply go extinct. Although gradualists do have a point, they fail to account for species adaptability to catastrophic events and rapid environmental change.

The concept of punctuated equilibrium attempts to fill in that gap in the gradualist hypothesis. It states that there are very long periods of environmental stability (or equilibrium), where no change in species occurs. Those stable periods are ‘punctuated’ by environmental crises or catastrophic events, which stimulate rapid genetic, physiological and behavioural changes.

To make the two concepts clearer, here is an illustration:

Gradualism (a) and punctuated equilibrium (b)

At the moment, there are also a few other theories on the rate of evolution which try to combine both gradualism and punctuated equilibrium. However, neither hypothesis is considered more correct than another and, funnily enough, the fossil evidence is used to support both. In my view, it is very likely that the reality is more complex than our ideas, and that the rate of evolution varies with time, location and species.

Despite the ambiguity, understanding the concepts of gradualism and punctuated equilibrium is essential for the readers of this blog. Firstly, it helps us explain the evolutionary journey towards our current form, and secondly – maybe more importantly – it can give clues as to what will happen to us in a changing climate.  

If you want to read on the theories in more detail, here are some useful resources:

• Gould, S. J. and N. Eldredge (1977) ‘Punctuated equilibria: the tempo and mode of evolution reconsidered’, Paleobiology, 3, 2, 115-151
• Saylo, M.C., C. C. Escoton and M. M. Saylo (2011) ‘Punctuated Equilibrium vs Phyletic Gradualism’, International Journal of Bioscience and Biotechnology, 3, 4, 27-41

And my personal favourite (pages 315-330 are relevant to this post, but the whole book is worth reading):

• Van Andel, T. H. (1994) New Views on and Old Planet, Cambridge: Cambridge University Press