Have we seen it occurring in the last ~150, i.e. since the last time there were famines in e.g. Europe? No. 150 years are only six generations. You need to have sequenced a lot of genomes to see evolution, i.e. changes in allele frequencies, over as few as six generations - unless there has been a catastrophe that has wiped out specific parts of a population. Currently, work is still ongoing to sequence even 1000 genomes. Current data allows identifying selection over the last few thousand years, i.e. ~100 generations, for example in adaptation of people in the Andes and Tibet to life under low oxygen conditions (see this article from PNAS).
In short, we cannot observe evolution through natural selection (which Darwin termed "natural" to differentiate it from breeding) in humans over very short timescales at the moment. However, we can observe evolution, i.e. change in allele frequencies, due to "breeding" in humans, such as caused by sex-selective abortions, which is shifting the ratio between boys and girls in some countries.
However, there is theoretical and empirical evidence that evolution is most likely speeding up due to the growing human population.
A recent paper in PNAS describes observable microevolution in humans between the late 18th century and mid-20th century. The authors use phenotypical analysis and statistics and conclude that the changes are not compatible with genetic drift.
It is often claimed that modern humans have stopped evolving because
cultural and technological advancements have annihilated natural
selection. In contrast, recent studies show that selection can be
strong in contemporary populations. However, detecting a response to
selection is particularly challenging; previous evidence from wild
animals has been criticized for both applying anticonservative
statistical tests and failing to consider random genetic drift. Here
we study life-history variation in an insular preindustrial
French-Canadian population and apply a recently proposed
conservative approach to testing microevolutionary responses to
selection. As reported for other such societies, natural selection
favored an earlier age at first reproduction (AFR) among women. AFR
was also highly heritable and genetically correlated to fitness,
predicting a microevolutionary change to- ward earlier reproduction.
In agreement with this prediction, AFR declined from about 26–22 y
over a 140-y period. Crucially, we uncovered a substantial change in
the breeding values for this trait, indicating that the change in AFR
largely occurred at the genetic level. Moreover, the genetic trend was
higher than expected under the effect of random genetic drift alone.
Our results show that microevolution can be detectable over relatively
few generations in humans and underscore the need for studies of human
demography and reproductive ecology to consider the role of