There have always been big cocks, but until recently we haven't had the means to view them erect, or measure and collate worldwide statistics. It is possible that better nutition could lead to larger cocks, but it seems that the real correlation is adolescent testosterone levels, which is genetic rather than environmental.
Recently, two compressed evolutionary traits have been noticed. Until recently, African women were typically shortish and stocky, because that's how African men like their women. Over recent years, the European build (tall, slim, long-legged) has been available via magazines, films and the like. And it has been noted that the latest generations of women in Africa are taller, slimmer and longer-legged than previously.
The other trait is also to do with women, but this time white women. Women's attractiveness has changed dramatically over the last 100 years or so, or even more recently than that. Men have not improved in the handsomeness score, however. We now have many images of attractive women, compared to past times. If you look at pictures taken of women, say, in the late nineteenth and early twentieth centuries, you will see a lot who are rather 'plain'. Look around the streets today, and omitting those who are overweight and obese, how many plain women do we see? Not many.
Evolution is often thought to be slow and steady and incremental, but that isn't always the case.