Short-term waves ride on top of long-term waves, but if we want an accurate picture of reality, we need to simultaneously remember the short-term and long-term waves. The trough of one wave can mitigate the peak of another wave, should their frequency be off in such a way that they interfere with each other. Likewise, with social trends. Any article about what men think about marriage and fatherhood should be juxtaposed with the facts about the rise of single-parenting (and the fact that the majority of single parents are women).

There are a variety of sources that can be quoted on this issue, and depending which source you look at, you will see different numbers. However, my point is not about any particular set of numbers, but only about the need to remember the underlying trend. Just for the sake of having an example, I'll post one set of numbers, but no one should treat these numbers as being especially accurate:

"About 4 out 10 children were born to unwed mothers. Nearly two-thirds are born to mothers under the age of 30. ...According to U.S. Census Bureau, out of about 12 million single parent families in 2014, more than 80% were headed by single mothers."

https://singlemotherguide.com/single-mother-statistics/

Although any particular set of numbers can be questioned, the trend is beyond all doubt: the number of single-parents in the USA (and much of Europe) is increasing.

This trend overlaps with another trend, which is the big increase in divorce in the USA, which occurred between 1900 and 1970. The book by Carter and Glick (1976) looked at this data in great detail. In 1900 the USA had a divorce rate of 5%, whereas by 1970 the rate was close to 50%.

Since 1980 the divorce rate in the USA has declined slightly, but it remains high compared to earlier eras. More than 35% of all marriages end before their 20th anniversary.

When you combine the 40% single-parenthood statistic with the 35% divorce rate of 20 years, you end up with a figure of almost 75% of all children being born into unions that do not last during the years the child is growing up. However, it is worth noting, the 40% and the 35% are not mutually exclusive groups, so the rate is not actually 75%. Some people become parents while they are single, but they later get married. But this number doesn't dramatically shift the reality: the vast majority of kids come from romantic unions which are over before the child reaches their 18th birthday.

The people most likely to remain single while parenting fall into 2 groups: the very poor and those who are culturally non-conformists. A side-effect of the above trends is that the men who do get married tend to be more traditional than the average. Whereas 50 years ago there was no political division regarding marriage, in the future we can expect considerable political differences between those who have kids inside of marriage, versus those who have kids outside of marriage.

Some people regard the advent of single parenting as a radically modern phenomenon but it is worth considering it in light of the Grandmother Hypothesis, which explains menopause in women partly as a way of funneling needed resources to grandchildren. This theory is highly controversial. An early study concluded that in the Hazda tribe, the majority of all calories going to children came from the child's grandmother, although recent studies have disputed that, and it seems clear that the majority of protein comes from men who go hunting:

"On the whole, [men] contribute 43% of all daily kilocalories arriving in camp, but 50% among married couples, and 69% among those with nursing infants (Marlowe 2003a)"

http://www.unl.edu/rhames/courses/ppoint/menopause-short.pdf

That evidence can be read either way, but if you are traditionalist, and you believe women with young children are typically dependent on men, I think the surprising thing about this research was how many calories are brought in by the grandmothers. Whether that figure is 40% or 60% seems to me a minor point, the larger point is that is an important percentage. More so, I would guess that if a man went missing (died in war, died of disease, etc) the grandmother might then step up her efforts to bring in more calories for the children. So at least some aspects of single-parenthood have ancient roots (indeed, men have always died in war).

Those are the long-term trends.

There are medium-term trends, such as the decline of male wages since 1973, which forces men to work longer hours. Whereas in 1973 the typical American worker had more vacation time than the typical European worker, the situation has now dramatically reversed. The German worker regards 8 weeks of vacation as their sacred right, whereas most American workers can hardly dream of getting so much vacation time. This reality limits the amount of time that men can spend with their kids.

Then there are the short-term trends, such as the high levels of unemployment brought about by the Great Recession of 2008. Whatever ideals a young man might have about marriage and child rearing, the economic environment has been challenging for all but a privileged few.

I don't mean to imply that any of these trends are necessarily The Absolute Truth about fatherhood circa 2015, I only mean that to have an accurate read on the situation, one has to remember all of the trends, and how they happen to conjunct at the current moment.