Evolution favors neither side in chicken-or-egg mystery

Which came first, the chicken or the egg? This is a very old question, and it seems at first to have no definitive answer.

Many problems like this one are confusing because we look at them the wrong way or ask the wrong questions. In this case the confusion arises from two erroneous assumptions: one or the other must come first and both the chicken and the egg are unchanged from the beginning.

Use an evolutionary approach and the conundrum evaporates.

In the fossil record, single-celled organisms were around for several billion years before cells learned to cooperate and specialize to form multicellular organisms. Because a chicken is a highly evolved multicellular piece of biology and an egg is a single cell, it might seem natural to assume that the egg came first. But where did the first egg come from?

From an evolutionary perspective, the chicken and the egg co-evolved. As a mental exercise, we can trace it all the way back to the first sexual reproduction 3 billion years ago when all life on earth was unicellular and reproduced asexually. Before that time, reproduction took place through an asexual process of cell division. The most advanced form of life then was a single-celled amoeba-like organism that made identical copies of itself by splitting in half.

There are single-celled prokaryotic organisms living today that reproduce in this manner. It is very efficient, but it produces offspring that are genetically identical to the parent cell.

A major advancement in reproduction was the sexual revolution. Somewhere around 2.6 billion years ago the ability to mix genetic material between organisms arose. The breakthrough was containing the genetic material in the nucleus of the cell. This is the way that more highly evolved organisms such as us and chickens reproduce. With the advent of sexual reproduction, genetic material from one individual is combined with that of another. This has several advantages, the most important being that offspring are genetically similar to both parents, but not identical to either.

Because of this variation, some organisms are more fit than others and may pass on those traits to successive generations.

The offspring have traits inherited from both parents, but no two are identical except in the case of identical twins.

So what about the chicken and the egg?

From that very first combination of genetic information within the cell nucleus, all complex organisms have evolved. As that occurred, organisms also evolved several different ways of protecting the young until they are mature enough to survive in their environment. The more complex and the larger the offspring, the more time is required.

For reptiles, amphibians and birds, it is the egg that nourishes and protects the offspring until it is strong enough to break the shell and face the world. For mammals it is the womb or the pouch that provides a safeguard until the little one is capable of surviving outside of maternal protection.

So which came first? The answer must be neither and both.

Richard Brill is a professor of science at Honolulu Community College. Email questions and comments to rickb@hcc.hawaii.edu.