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http://m.pnas.org/content/107/3/961.full

Thus, although there is considerable uncertainty in the preceding numbers, it is difficult to escape the conclusion that the per-generation reduction in fitness due to recurrent mutation is at least 1% in humans and quite possibly as high as 5%. Although such a mutational buildup would be unnoticeable on a generation timescale, over the course of a couple of centuries (approximately six generations), the consequences are likely to become serious, particularly if human activities cause an increase in the mutation rate itself (by increasing levels of environmental mutagens). A doubling in the mutation rate would imply a 2% to 10% decline in fitness per generation, and by extension, a 12% to 60% decline in 200 years.

Is this correct and unavoidable?

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    What pseudoscience babble is this? What is 'fitness'? Mutation IS evolution, only the environment can decide whether a mutation is 'deleterious '. If we're trying to say that mutations are causing imperfections then we have to start by defining a 'perfect' human state. And that is what we call 'Eugenics'. All mutations are good mutations as far as evolution is concerned.
    – Richard
    May 18, 2017 at 13:25
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    Is a very similar question, but I'm not convinced it's a duplicate.
    – user11643
    May 18, 2017 at 15:39

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Natural Selection works only if the unfit don't reproduce at the same rate as the fit. Since the percentage of humans born who eventually reproduce is at massively high and unnatural numbers, it goes to follow that there is little Natural Selection affecting the population genome.

There are numerous sources saying the same. Consider, for example, Sir David Attenborough: Humans have stopped evolving

Human beings have stopped evolving after becoming the only species to “put halt to natural selection of its own free will”, Sir David Attenborough has said, as he predicts the “cultural evolution” of the future.

Sir David, whose new show concentrates on the ascent of man, said he believed humans had now stopped evolving in physical terms, after developing means to keep even the weakest of the species alive.

Saying we are now able to rear up to 99 per cent of our babies, he added people were no longer subject to Darwinian theories natural selection.

Save for reproductive issues that medicine cannot overcome, there's no reason to think that the unfit reproduce more or less than the fit, when averaged out among the world's billions of people.

If it's good enough for Attenborough, it's good enough for me.

Now, the claim in the question's source goes a step further, saying the human genome is deteriorating. Maybe, but that's really a matter of perspective. If medicine can keep up with mutations and genetic drift that would otherwise be harmful, then it doesn't really matter. And if it can't keep up, well then Natural Selection will kick in again.

A more neutral term would be the human genome is "broadening". But this can be viewed as a good thing to. With a broader genome, the species is more likely to survive devastation from sudden environmental change, such as a plague.

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