Natural Blondes are caused by a recessive gene that means that no melanin is produced in the hair folicle.

Both parents have to possess the blonde gene for a blonde child to be born.

Currently recessive conditions are in decline world-wide. This is because the human populations are out-breeding at quite a fast rate, and this means that the chances of these genes meeting each other is very low. This is good because quite a lot of genetic diseases are necessarily recessive. Necessarily because otherwise evolution would tend to have removed them from the population. So genetic diseases are declining through dilution.

Alas! This also means that true blondeness is doomed also. The current estimate is that blondeness will be all but extinguished in about 200 years, if nothing were to be done- the last blondes are likely to be in Finland.

The WHO has denied doing any studies into this issue, so it may very well have been misreported; nevertherless IMO it is likely that the number of natural blondes will go down over time.