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The paper referenced here:
Yann Leseque et al. A Resolution of the Mutation Load Paradox in Humans. Genetics 2012; 191: 1321-1330.
could provide a way into the literature on accumulated mutation damage in other species.
There seem to be a number of variables to consider - how many new mutations per generation, what proportion of offspring survive, how fast the population is growing and probably others.
Although this literature says 88% mortality or 12% surviving, this is only approximate - and there would have been considerable variation at different points in history.
It also seems a bit high for human reproductive capability - since hunter gatherer women seem seldom to have more than six children (due to late menarche, the children spaced-out by the contraceptive effect of lactation, prolonged lactation and then low fertility from age c 40) - which would not be enough.
So I guess the real number would be more like an average 1/4 or 1/3 of human offspring surviving for most of the time and in most places.
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What about about delayed reproduction in modern populations?
Delayed reproduction leads to more chance of mutations (eg from sperm) and problems with poorer quality control on release of older eggs (eg trisomy twenty one is probably the tip of an iceberg of similar problems).
But late reproduction also reduces the number of generations and the possibility of mutation accumulation from that cause - so that modern people only have two generations (e.g. average thirty plus years) - i.e. two new lots of mutations in sixty-something years - where in historical times there would have been three generations per 60-70 years - three lots of new mutations.
So slowing reproduction (by increasing the average age of reproduction) may perhaps reduce mutation accumulation temporarily; given that the effect of aging on mutations may be less per decade than the effect of an extra generation of new mutations.
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This was originally a comment at a new blog called Brain Size
http://brainsize.wordpress.com/2014/06/30/could-genetic-iq-really-have-declined-so-much-so-quickly/
Which is shaping-up to be a valuable contribution to intelligence research.
The author, Herr Professor Doktor Pumpkinperson, has the attributes of honesty, persistence (this especially), intelligence and a refreshing disinclination to take offense at the criticism of others!
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