By Dr. Anthony Policastro

It has been almost 200 years since Charles Darwin published his theory of evolution. One of the key tenets of that theory is survival of the fittest.

That tenet has played itself out multiple times throughout history. Scientists have been able to trace life on earth back to about 540 million years ago.

About 444 million years ago, we had what is known as the First Extinction Event. Ice age changes during that period resulted in massive changes in climate both on land and in the sea.Approximately 86 percent of species on earth became extinct. The remainder continued on.

About 84 million years later (360 million years ago) there was another period of cooling. This caused what is known as the Second Extinction Event. About 75 percent of species on earth became extinct, the remainder continued on.

About 90 million years later (250 million years ago) there was intense volcanic activity in Siberia. This caused global warming, it caused acid rain and acidified ocean waters. It was the Third Extinction Event. This time about 96 percent of species became extinct. The few remaining species continued on.

About 50 million years later (200 million years ago) underwater volcanic activity caused global warming and a dramatic change in ocean composition. This was the Fourth extinction event. Approximately 80 percent of species became extinct and the reminder carried on.

Then, about 135 million years later (65 million years ago) an asteroid impacted Yucatan, Mexico. It again resulted in rapid cooling. This was the Fifth Extinction Event. This time 76 percent of species went extinct. The dinosaurs were the best example of this period. The remainder carried on.

That brings us to today. All the other extinction events occurred between 50 and 135 million years apart. The last one was right in that ballpark at 65 million years ago.

Most of them were because of weather phenomena that was uncontrollable. But they all had one thing in common. Only the fittest species survived.

It is highly likely that there will be another extinction event in the future. It may be millions of years away. It might occur suddenly with a change in volcanic activity. It might occur gradually with a warming of the planet to a level that caused the Third and Fourth Extinction Events.

If and when that happens, we can expect a similar result to the other events. More than three quarters of the species on earth will die. There will be survival of the fittest. The real question is whether the human species will be one of the survivors or not.

Perhaps Charles Darwin knew the answer to that. We certainly do not.