LOS ANGELES, CA (Catholic Online) - According to researchers, the evolution of birds may have a lot to do with it. As it is now understood, birds evolved from dinosaurs and they preyed on giant insects. This created evolutionary pressure and natural selection began to favor smaller bugs that were more difficult to find and catch.

Giant insects first evolved thanks to the oxygen rich atmosphere of the prehistoric earth. Studies have shown that large insects prevailed at a time when birds did not exist and oxygen levels were high. These findings have been supported by modern research with insects raised in oxygen-rich environments. 

Fossil evidence shows some of the bugs were as large as a modern duck.

However, the evolution of birds appears to have changed the game for large insects. About 150 million years ago, despite high oxygen levels in the atmosphere, insects became smaller. This is the same time when birds appear in the fossil record. 

According to the theory of natural selection, this would be because smaller insect offspring would be more likely to survive and reproduce than large offspring, who would be more likely to become food. 

As the small offspring survived and the large were consumed, traits for small size became dominant and eventually large insects became extinct, replaced by smaller species. 

Researchers say further study is needed to confirm the hypothesis including studies on how changes in oxygen levels affects different insects over time, as well as seeking more fossils that would affirm, or invalidate the hypothesis.

All this leaves just one question. If the bugs were as large as birds, just how big were the birds that ate them?

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