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Friday, 13 January 2012

Something Fishy About Creationism

East African Lakes
The lakes of East Africa with their diverse populations of a group of related species of cichlid fish provide a superb example of radiating evolution over a very short time scale and so are a major problem for creationism. These fish represent an aquatic version of Darwin's finches, and are, if anything, an even more dramatic example of the way new species arise by evolving into new ecological niches and an example of the very short time-scale over which this can occur. See The root of the East African cichlid radiations.

First a little about the lakes and their geology:

Between 17,000 and 16,000 years ago, towards the end of the last Ice Age, there was a surge of icebergs and glacial meltwater into the North Atlantic which altered ocean currents and changed the weather pattern over the African and Asian monsoon areas, which experienced a resulting mega-drought. Analysis of sediments show that this caused Lake Victoria, Lake Albert and Lake Tana to dry up and disappear.

A similar event 14,000 - 15,000 years ago caused Lake Victoria to dry up again and a subsequent lowering of water levels 5,000 years ago left a small satellite lake, Lake Nabugabo, isolated. So, from this we know how long ago each lake received its founding population of cichlids from their feeder rivers. In the case of Lake Victoria, this was between 14,000 and 15,000 years ago. We also know that the micro-lake, Lake Nabugabo, has been isolated for just 5,000 years. By contrast, nearby Lake Tanganyika is tens of millions of years old and has remained filled for all that time. See AfricaPaleo - FOCUS 1: Lake levels and evolution.

Cichlids are a group of fish which have two very interesting unique characteristic:

  • They have evolved a set of pharyngeal 'jaws' in their throats by fusing their lower pharyngeal bones into a single structure and a set of muscles to operate them as a secondary set of jaws, giving them the ability to exploit a wide variety of food sources.
  • They are protective brooders, frequently mouth brooders: they lay a small number of comparatively large eggs which are carefully guarded and the fry continue to receive parental protection.
These two things are believed by biologists to be responsible for the cichlid's ability to exploit new niches and so radiate into new species from a founder population.

Just a few of the Lake Victoria Cichlids
Today, in just 14,000 - 15,000 years, Lake Victoria now has or recently had, some 500 different species of cichlids. This represents approximately twenty-two 'branching' events where each species splits into two, in other words, every branch of the diversifying tree needed to sprout a new branch twenty-two times on average so each species needed to give rise to a new one every 650 years on average.

A series of ecological disasters have recently severely reduced Lake Victoria's cichlid population so that some 300 species are now endangered or have become extinct. These disasters include siltation as a result of deforestation and soil erosion, introduction the the Nile perch and the water hyacinth and over-fishing.

I should point out that there is not full agreement in the scientific community on this time-scale. Mitochondrial DNA analysis, using a hypothetical mutation rate, suggests the current diversity took between 100,000 and 200,000 years. These two widely different time-scales could be resolved in two ways: firstly, the assumptions in the hypothetical mDNA mutation rate may not be valid; secondly, there could have been a few small deep pools in which earlier populations survived the dessication. The survival of a diverse population in small pools seems unlikely however and the analysis of the sediments seems conclusive, so on balance the shorter time-scale seems the more plausible.

Never-the-less, 500 new species over even the longer time-scale is impressive.

So, what creationists need to explain is how this rapid radiation into some 500 new species occurred when they argue (or should that be 'assert'?) that: a) there has not been enough time; b) 'macro-evolution' is impossible.

Once again we see the observable facts don't support creationism. (Tweet this)

And once again we see creationists refusing to take reality into account when it isn't what they want it to be.





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2 comments:

  1. Ah, but the world is only 6000 years old as all creationists 'know', so something in your argument must be fallacious (I don't think).

    Nice post, as usual.

    ReplyDelete
  2. Give the Creationists time, they'll think up some new lies to try to dodge this problem, just as Intelligent Design was meant to do before being laughed out of any serious discussion.

    ReplyDelete

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