Micro-Evolution's Limits

by Stephen Caesar

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As discussed often in this column, micro-evolution within species occurs frequently in nature. When a species endures outside stresses, such as environmental change or parasitic attack, its genetic code will flip an "on-off" switch, causing it to undergo minor changes that will give it a greater ability to deal with these stresses. Evolutionists claim that "macro-evolution is micro-evolution writ large," meaning that, over millions of years, microevolutionary changes will cause the species to evolve into a completely new, more advanced species (such as fish evolving into four-footed animals).

However, macro-evolution fails for two reasons:

Incremental changes only go so far before hitting a "ceiling," above which no changes occur;

When a species undergoes micro-evolutionary change in one area, it undergoes decline in another. If an organism micro-evolves an improved ability, say, to resist parasites, it may wind up living a shorter life, or being weaker or smaller, or having fewer offspring. This is called "fitness cost" or "fitness trade-off" (Buckling et al. 2003: 2107).

In the wild, many species undergo micro-evolutionary changes when they fan out from a common starting point and occupy different ecological niches (deserts, jungles, tundra, woodlands, etc.). Over time, different on-off switches in their genetic make-up will cause them to develop into different strains. However, one niche species is not an improvement over the other: each one is merely adapted for its specific niche. Angus Buckling and Matthew Wills (Department of Biology and Biochemistry, University of Bath, England), and Nick Colegrave (Institute of Cell, Animal, and Population Biology, University of Edinburgh, Scotland), conducted experiments on the bacterium Pseudomonas fluorescens that confirmed this.

The three researchers took six cloned (thus genetically identical) batches of P. fluorescens and allowed them to colonize different ecological niches in a laboratory. Rather than witnessing the different niche species macro-evolving into new, improved species, the scientists observed the following: "As predicted, populations increased in fitness through time but showed a greatly decreased ability to diversify. These results show that niche specialization may come with a cost of reduced potential to diversify" (ibid.). This is fitness trade-off in action.

The scientists reported that "adaptation itself is likely to limit a population's ability to diversify, when evolution occurs in rugged fitness landscapes'" (ibid.). All six batches of bacteria were raised in different environments, and the scientists transferred each batch to a new environment six times. They reported: "In all lines, diversification after six transfers was much less than ancestral diversification, and there was an overall negative correlation between transfer number and ability to diversifybetween fitness and ability to diversify" (ibid. 2108).

Simply put, this means that with each transfer to a new environment, each batch of bacteria became less and less able to diversify-just the reverse of Darwinian expectations. This is micro-evolution hampered by fitness-cost occurring before our eyes.

They concluded: "Adaptation can limit the ability of bacterial genotypes to diversify genetically. This was not the result of generalist evolution or the evolution of an intrinsic reduction in evolvability, but was caused by environment-specific adaptation" (ibid. 2109).

You can adapt or diversify-but you can't do both. Evolutionists predict that both should happen, with no trade-off occurring. Over time, each batch of P. fluorescens should continue adapting and diversifying until they become new, improved, separate species, all having evolved out of a common ancestor. This simply has not happened, nor can it. The ceiling has been reached.

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Reference:

Buckling, A., et al. 2003. "Adaptation Limits Diversification of Experimental Bacterial Populations." Science 302, no. 5653.

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Stephen Caesar holds a master's degree in anthropology/archaeology from Harvard. He is a staff member at Associates for Biblical Research and the author of the e-book The Bible Encounters Modern Science, available at www.1stbooks.com.

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