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Unless a lake is considered polluted, we don’t reflect much on all the living organisms that the waters contain. As a matter of fact however, most lakes have many different kinds of single celled plants (algae) floating happily in the top several metres of the water column. While in certain situations, people say that variety is the spice of life, many scientists worry about why there is such diversity/variety in lakes and the sea.

Various experts have reflected on the amazing diversity/variety of algae that we see floating in lake waters and in the sea. One ecologist wrote an article in 1961 entitled “The Paradox of the Plankton”. Plankton means tiny floating organisms and can refer to plants or animals. If Darwin’s ideas about natural selection are correct said Dr. Hutchinson, then at least in summer when there is likely to be a shortage of nutrients “we should expect that one species alone would outcompete all the others so that in a final equilibrium situation the assemblage would reduce to a population of a single species.” (G. E. Hutchinson. American Naturalist 95 #882 p. 137) Of course the point of this article was to speculate on reasons why, while evolution remained true, evolutionary expectations were not met. Biologists are still reflecting not only on the amazing diversity/variety of organisms that exist, but also on the amazing variety of species that are able to live together at one time and in one location.

A book published in 2005 was entitled Demons of Eden: the Paradox of Plant Diversity (Jonathan Silvertown. University of Chicago Press). The book was written to consider the problem of the vast diversity of plant species. With the concept of natural selection (Darwin’s idea) in mind, one reviewer of this book pointed out: “one might predict that one supremely fit plant species, capable of photosynthesis, vegetative growth, pollination and seed dispersal in a way that outperformed all other plants, might ultimately prove the victor in the evolutionary struggle and would dominate the world’s primary production. But this has not happened.” (Nature Nov. 3/05 p. 27) Instead, the reviewer points out, we see an extraordinary diversity of plant species, about 400,000 according to some estimates. It might make sense that a few plants would win out in a struggle for survival, scientists might imagine, one in each kind of environment, but not the fantastic variety of shapes and life styles that we see in plants all over the world.

The issue of why there is so much more biodiversity than expected grows ever more interesting. Lately biologists have turned their attention to organisms in the soil, and they are amazed at what they are finding. Since the soil ecosystem consists mainly of microbes, apart from the obvious molds and mites, modern scientists have resorted to some fancy new techniques to find out about the tiniest organisms. Microbes like bacteria are so small that it is impossible to identify them by visual means. Instead biologists have typically identified microbes by the way they act in laboratory cultures.  So, suppose a scientist sprinkles some soil on agar plates, or washes the soil with water and puts that on the culture plates. The agar makes a solid surface, firmer than gelatin. Scientists add nutrients to the agar which they think the microbes of interest will want to grow on. A few well known organisms typically appear in culture and these will be duly identified. Suppose however that there are other organisms in the soil and that these organisms do not like the culture conditions offered to them in the lab. They won’t grow. How then, if such species exist, will we ever find out about them?

In the late 1990s some scientists devised a new technique called “metagenomics.” This is a technique which is designed to show the existence of different species in soil even if they will not grow in cultures. Metagenomics means that a small sample of soil is treated in such a way that all the DNA (genetic material) in all the microbes therein is extracted. This is then run through a machine which reads the information content on each fragment of DNA. Computers then figure out which fragments were originally joined together in one long loop of DNA in a microbe. So now the computer knows how many drastically different collections of DNA this sample contained. The computer will ignore duplicate samples of the same thing, and just list the very different “genomes” (loops of DNA) from very different organisms.

Several such studies have shown that there is no overlap, but rather quite a difference between the genetic information in one microbe and that in another. (Nature Sept. 25/08 p. 482). So the scientists count up the numbers of different “genomes” and this gives them an estimate of the number of different microbe species in the soil sample.

Some of the estimated numbers of microbe species have been quite astounding. Numbers varying from 2000 to 10,000 to 50,000 species per gram of soil are not uncommon. A gram is an extremely small amount of soil. The next thing scientists have done once they got over the shock of such numbers, was to ask why there is such variety in the soil. According to one commentator: “Many species also seem to be redundant, eating the same foods and fulfilling the same ecosystem jobs, so scientists don’t quite understand why they’re there at all.” (Nature Oct 9/08 p. 725). Evidently there seem to be a lot of organisms with different genetic information but which do the same thing.

One ecologist researched this issue by means of experiments. He set up soil cultures in jars and added fungal species, one at a time. As each new fungus species was added, the culture did better to a maximum of six different species. But the original soil sample had contained 43 fungal species. Above the six species however, no improvement in the culture was observed. So the question of why there is so much diversity in nature remains unanswered for the vast majority of scientists.

It is obvious that nature does not fit evolutionary expectations about diversity. Instead the tremendous richness and variety are clearly a matter of choice on the part of the Creator. God did not just create useful designs, he lavished upon the creation artistic and amazingly varied designs. He did this to make nature interesting and beautiful. Not only are the richness and diversity of coral reefs and the rainforest a mark of God’s creative hand, but so is life in lakes, the ocean, in soil and indeed in all the local natural communities with which we are familiar.


Margaret Helder
April 2009

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