Any scientific theory has to make predictions that can be falsified. A theory that makes no predictions, or one that cannot be falsified, regardless of whatever evidence comes along, is simply not science.
Darwin’s theory of evolution by natural selection has been accused of not being falsifiable, but this is not the case. One example of this is as follows.
When Darwin first proposed his theory of evolution, it soon became clear that evolution would take hundreds or – more likely – thousands of millions of years to create the complex life forms that now exist. But, at the time, it was believed by many that the Sun, and therefore our Solar System, could only be a few tens of millions of years old. The reason for this was that nobody could think of any way that the Sun could carry on shining for more than this period of time.
If they had been right, then Darwin’s theory would have been dead in the water.
But early in the twentieth century, Albert Einstein put forward his theory of special relativity, which includes one formula that everybody knows: E = mc2. The formula proclaims the equivalence of matter and energy, which can – in the right circumstances – be transformed into each other.
Sir Arthur Eddington
This gave Sir Arthur Eddington the idea that the Sun might be powered by the conversion of hydrogen to helium, with the emission of energy in the form of radiation, and we now know that this is correct. This mechanism provides an ample fuel source that enables the Sun to shine for billions of years. In fact, we now know that the Sun and the Earth are about 4.5 billion years old, giving ample time for evolution to have taken place.