MedMae wrote:I'm not convinced there is a reduced selection process going on or if it's just changed. For example in western society there is clearly a reduced significance on physical capabilities, but there is still going to be a high selective process going on in relation to cognitive abilities. Not just in intelligence but abilities to endure stress and concentrate.
Intelligence is likely to be a negatively self-selecting trait. It is hard to pick intelligence from education (and socioeconomic status) in our society, but intelligent/well educated people (most importantly women) generally don't start reproducing until later in life (if they choose to all). It tends to be the less intelligent/educated who start breeding at an early age, continuing to do so for longer, having more children in total, many of whom repeat the process. Being less intelligent/educated is actually a beneficial trait for passing on genes.
Nick wrote:I'm hazy about this, but it may stretch back to Malthus. The proposition is that it is the less able who breed more, and therefore that humanity is on a downward path. I'm not competent to examine thoroughly, though I'm inclined to think it is too pessimistic, but it would be an interesting starting point, to attack or defend as appropriate.
I think that the concept of a "downward path" is rather deterministic, since it applies that we are/have been/should be on an "upward path" - but towards what? Evolution is about breeding, not brains. The "less able" are those that don't breed, when we are talking in evolutionary terms. Someone might have an IQ of 72, no education, have no job and do nothing for society, but if they have ten kids (even if they are taken into care immediately) they are evolutionarily more successful than a Nobel Prize winner who has no kids.
I'm not sure I entirely agree with Steve on this, I can see where he's coming from, but use of the mean age of fathers does not reflect any pattern of the data. I'd like to see the raw data on this (or at least the range, standard deviation, median and a Kurtosis value), because the reduced average age could be due to be the result of a negative skew towards very young fathers (or even a binomial distribution of some young and some older fathers). Such a skew would shift the value of the mean, without it reflecting where the bulk of the data lie. Also, it would be interesting to see if the range of the data is greater than it was historically, since it may include a wider range of ages of men, so although the mean is lower, there could be more older men reproducing that there were historically. I also think that the narrow temporal range weakens the observation, since it wouldn't take much social change to shift the pattern.