Have batsmen gotten better or have bowlers gotten worse?

By Adrian Meredith

We all know the stats, but here is a rough rehash:

1877 (test cricket started) - batting average was 20-25 per batsman

1930 (Bradman's time) - batting average was 30 per batsman

1965 (Benaud's time) - batting average was 35 per batsman

1990 (Tendulkar started) - batting average was 40 per batsman

So why is this? Why are batting averages getting higher?