How do species change? According to Darwinists, physical differences result from the accumulation of small changes over many generations. But observations—like a recent report of steelhead salmon that changed in one generation—show that dramatic trait changes happen fast. What does that mean for the evolutionary concept of the way species develop?

While observing the migrating salmon population that inhabits Oregon’s Hood River, an Oregon-based team of researchers built detailed family trees of multiple fish generations. They used genetic fingerprinting to discover that after just one generation, fish that had been transported to hatchery ponds produced more offspring than their wild counterparts. However, the pond-bred fish didn’t fare very well when they were placed back in the wild.

The authors, publishing in the Proceedings of the National Academy of Sciences, wrote:

We have demonstrated rapid adaptation to captivity in a steelhead population….However, the trait values associated with success in the captive environment are detrimental in the wild, resulting in low reproductive success in the wild by fish from families that were successful in captivity.1

Thus, the fishes’ rapid success in the breeding pond came at the expense of their fitness in the wild, as measured by numbers of offspring produced.

How do these observations compare with various ideas about how species change? The authors correctly identified how traditional ideas of natural selection over many generations could be verified: If the “rapid fitness decline” that the fish experienced after adapting to the hatchery was the result of either a very high mutation load or of “many generations in captivity,” then natural selection could presumably explain the changes.1

But these fish only needed one generation to experience dramatic changes.

Moreover, the changes, which the study authors wrote were “possibly correlated,” occurred in multiple traits at once.1 And the evolutionary idea of random-based biological changes does not fit with such correlated changes….

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