A change in the environment – the arrival of poachers in significant numbers – drives a change in the DNA of animals living in that environment – fewer genes for large tusks.
Another change in the environment will drive another change in the DNA of animals in that environment. Evolution tracks changes in the environment and changes DNA to match those changes. In one environment large tusks are deleterious on average and so the genes for large tusks are disappearing from the population. If, later, large tusks become advantageous then those genes will increase in the population.
That is what evolution does: adjusts DNA to fit the environment.
rossum
This doesn’t reflect how evolution works.
Also, the example you provide of the elephant’s tusk is an adaptation, a capacity that is built-in to living organisms, and of which we take advantage in breeding animals. There is absolutely no proof for your claim of mutations driving the observed change.
Animals exist as parts of their environment. It is a relationship. The individual animal’s adaptability to its environment allows for its either reproducing or not. On the other hand, the environment chooses, albeit blindly. “Evolution” does not track anything. Evolution is a concept that represents what appears to have happened as the world changed in time.
Actually, Darwinism does not explain evolution, the appearance of a growing complexity of organisms over long periods of time.
There do occur mutations and the phenotype must be in sync with the organisms environment in order for it to survive until it produces offspring. We use the term reproduces, but according to Darwinism it would be a misnomer, since the organisms do not reproduce themselves if the offspring are of a different genetic make-up. As one example of a mutation that worked out, we observe that asymmetry may not necessarily be a detriment in the case of the founder. A story about its origins would include its ability to survive feeding on the bottom of the ocean, which also gives it some protection from predators. Looking at nature in general, such phenomena are rare.
Darwinism is in vogue because it fits the agenda of modern society in its worldly pursuits. It is easily adopted and propagated because the terms are poorly defined, it misuses the authority and power of science, and provides an interesting, although superficial story that links us to all creation. Unlike religions which draw on the Truth, it is more of a delusion, consisting of unproved assumptions are presented as justification for the belief.