First off, the major difference between the natural sciences and the human sciences is that the natural sciences study the natural world and the natural things in it, like atoms in chemistry, living beings in biology and forces etc. in physics, whereas human sciences study humans and how they are affected, like how psychology studies the mind, political science studying the political world and sociology studying the different societies. The reason that they are all ‘sciences’ is because the methods and ideas behind studying them are either the same or very similar, with some being more ‘sciency’ than others. For example, the natural sciences are very experimentally based, however so is psychology, but something like anthropology is not as experiment based, although it make occasionally use experiments and data.
At Oxford, there is a course called ‘Human Sciences’. According to the course page, it focuses on ‘ the evolution of humans and their behaviour, molecular and population genetics, population growth and ageing, ethnic and cultural diversity and human interaction with the environment, including: conservation, disease and nutrition’. Personally I find the course very interesting, and I think it sums up almost all of the human sciences by encompassing them all into one course. However, (as far as I know) there are not many (or any degrees) offering the same kind of initiative for the natural sciences. Is this because they are not as interlinked, or is there too much material to cover? After some (a good 2 minutes) consideration, I think (although there is a lot more actual knowledge and facts to cover) that the core reason is because the natural sciences are more separate, or ‘purer’ than the human sciences. For example, anthropology – it covers so much, from ancient cultures to current human behaviour and linguistics, and crosses over into so many other human sciences (sociology, criminology, even law) and other subjects like history. In contrast, lets take physics – it focuses on matter, motion, energy and force, and while it applies to many other aspects of life and other subjects, it does not have nearly as much coverage of other subjects like any of the human sciences do.
To sum up, the natural sciences and the human sciences are equally sciences, but the natural sciences are more scientific in their methods, and the natural sciences study the natural world whilst the human sciences study humans themselves.