Modern-day people are as smart as their ancestors of old. As smart, not more so or less so. For there have been, are, and always will be those who are smart and those who are less so. The very nature of the human brain and of society dictates as much. Mental ability can be measured in two ways, that of intelligence, or the efficiency, number and complexity of mental operations, and of knowledge, that of measuring the amount of data contained in a brains memory, or more correctly the amount one can access, as much of a typical humans memory can not be readily accessed.
The amount of ones memory's data that one can access at any time one wishes to is a good indication of knowledge levels and intelligence levels with a single measurement. It shows how efficient ones brain is and also how much information one can retrieve. Thus it can be seen that knowledge and intelligence are closely linked, if not the same entities. When deciding whether or not humans are smarter than their ancestors it must be remembered that whilst society has changed much in recent years, the structure of the human brain, and the way society functions, have not.
Whilst the car did not exist in 1 AD, for instance, the wheel did. And both a horse drawn vehicle and a car serve the same purpose. Thus it can be seen from this simple example how whilst society is a constantly evolving entity, the way it operates and the reasons why it operates in those ways remain much the same. The human brain unlike society has had little change of any sort, like much of our structure, and is largely influenced by nurture, not nature.
The human brain must be thought of as an organic computer. It has evolved over time to handle 'calculations', and in many respects is similar to its electric cousin. However it differs in a number of important areas. Firstly it is not built to be programmed by a human. It has evolved to handle primitive conditions and whilst it is on a higher level of complexity than most animals it is still not designed to be used in the way one would a desktop computer. One can, for instance, not access any file one wants merely by using an efficient search mechanism, nor can one store files in folders.
Well, actually one can, but as Sherlock Holmes proves, it requires dedication and persistence, not to mention energy and stimulation, that most humans lack and do not require. Thus most peoples brains operate on a very instinctive and predictable fashion. For instance, if one feels thirsty, one's brain tells one to get a drink. In most ordinary circumstances even though one is capable of far more complex abstract thoughts one chooses only to exercise this to a limited degree.
However some individuals choose not to be, or are forced or influenced not to be, constrained by these limitations. Most people with a career, that is not a string of barely connected jobs but a profession, apply themselves to this profession and show what human brains are capable of if one tries hard enough to control them. A physicist, for instance, or an astronomer, will be able to amaze one with their knowledge on various complex things. But if one were in their situation one would know as much.
Society has always had individuals of a higher intelligence than others. Society is not constructed of a single class of human, and as such there will always be, whilst society has anything similar to its present system in operation, those of a higher intellectual level and those of a lower level. Thus one's ancestors were not smarter than one, and one not smarter than them, but, if one combines all the intelligent people in the world today, due to today's higher population figure, society itself is smarter on the whole.