Darwin's contention that the strong survive and the weak die can be seen throughout history. For example, there are numerous examples of human populations becoming more resistant to diseases, as the 'weak' die and are unable to reproduce, while the 'strong' survive to contribute genetically to future generations.
In the book Guns, Germs and Steel: The Fates of Human Societies, Jared Diamond chronicles how Europeans living in cities allows plagues to spread rapidly, with those surviving and reproducing being resistant or better able to recover. The result is a more resistant population. In contrast, when Europeans traveled to the new world, bringing germs with them, the native American populations, who had never been exposed to these particular diseases, were decimated, undergoing the same process as Europeans experienced earlier.
Similarly, in cultures where communal drinking containers were used (ie kava vessels in Fiji), many diseases were transmitted to the entire group, again resulting in a more resistant population over time.
One way that human populations differ from the other organic populations described by Darwin is the human use of drugs, vaccines, and sophisticated medical medical procedures to treat diseases, injuries, and medical conditions. These go beyond the genetic makeup of a person, and make the 'selection' process more complex.
For example, the rise in cesarean births allows babies with larger heads to be born and survive, when otherwise, the result would often be death of the baby, the mother, or both. This medical procedure allows infant head size to increase over time, perhaps with other results, such as increased brain size and any accompanying benefits (or disadvantages) that might produce.
In a disease context, the use of AIDS medications allows more people with AIDS - who would have otherwise have died, if they lacked natural resistance - to survive & reproduce.
Another difference in human populations is the use of clothing, buildings, and technology to survive changes in environment. While animal & plant populations are largely limited to natural genetic variation for members to survive changes in environment (or migration to areas with more favourable conditions), human populations are able to use technology to expand into new territories or to survive environmental changes. For example, human beings do not need to grow their own fur coat to survive life in the Antarctic, but can build & heat suitable home or research facilities & can wear synthetic coats (or wear the furs of other animals) to survive, changes that do not require genetic change in the population.
Thus, Darwin's principle of the strong surviving & the weak dying can be seen in action throughout history. However, in human populations, medical and other technologies allow the survival of individuals who would otherwise have died, if genetic variation within the population alone was responsible for survival.