Origin of Hemoglobins: A Repeated Problem for Biological Evolution

Origin of Hemoglobins: A Repeated Problem for Biological Evolution

It’s football season again! And one of the big questions on every fan’s mind is, Can the New Orleans Saints repeat as Super Bowl champs? Even though the Saints are expected to have a good season, it is hard for any team to win the Super Bowl in back-to-back years. The last team to accomplish this feat was the New England Patriots.

Repeating as NFL champions is difficult because each season is filled with contingencies. Star players can get hurt, the referees can blow a call at a key point in a key game, bad teams can catch a lucky break, etc.

Evolution Doesn’t Repeat

The evolutionary process shares something in common with the NFL season: it too is characterized by contingencies. Late evolutionary biologist Stephen Jay Gould espoused the concept of historical contingency in his book Wonderful Life.

According to historical contingency, chance events govern biological and biochemical evolution at its most fundamental level. Evolutionary pathways consist of a historical sequence of chance genetic changes operated on by natural selection, which, too, consists of chance components. As a consequence, if evolutionary events could be repeated, the outcome would be dramatically different every time. The inability of evolutionary processes to retrace the same path makes convergence—the repeated and independent appearances of the same biological and biochemical designs throughout nature among unrelated organisms—highly unlikely.

As I noted last week, the unlikely appears to be the reality. Evolutionary biologist Simon Conway Morris points out in his book Life’s Solution that convergence is a widespread feature in the biological realm. (For examples of convergence, go here, here, and here.)

In my book The Cell’s Design, I document over one hundred examples of convergence at the biochemical level. If historical contingency truly reflects the nature of evolutionary processes, then I argue that the widespread convergence of such a broad range of biochemical systems raises significant questions about evolutionary explanations’ validity.

Hemoglobin in Jawless and Jawed Vertebrates

Recent research has identified yet another example of repeated origins in the emergence of hemoglobin in both jawless and jawed vertebrates.1 Found in vertebrates’ red blood cells, hemoglobin is the protein that binds oxygen when blood flows through the gills or lungs and, thus, transports this important molecule to various locations within the body.

Hemoglobin belongs to the globin protein family, a group that shares common structural features. The globin family includes myoglobin, neuroglobin, and cytoglobin. All of these molecules bind oxygen in muscles or the brain, giving these tissues oxygen storage capacity.

Evolutionary biologists believe that hemoglobin originated from an ancestral globin molecule through the process of gene duplication (in which a number of globin gene copies were generated through chance events). These duplicated genes were then co-opted to generate an oxygen transport protein (hemoglobin). Once it originated, this protein became encapsulated within erythrocytes (red blood cells). These scientists claim that this encapsulation provided an evolutionary advantage because passive diffusion of oxygen in the blood is not sufficient to sustain the high metabolic demands of large complex creatures.

Traditional evolutionary scenarios viewed the hemoglobin molecules found in jawless vertebrates as transitional to the ones found in the jawed vertebrates because of some structural and functional differences between them. Research by scientists from the University of Nebraska indicates that this is not the case at all.

When analyzed from an evolutionary perspective, it appears as if the hemoglobins originated independently in jawless vertebrates and jawed vertebrates. According to the latest work, it seems as if ancient globin genes underwent duplication separately, then were co-opted to generate hemoglobin molecules that, in both instances, became encapsulated within erythrocytes. In other words, this work seems to indicate that not only did these highly similar biochemical and physiological systems emerge independently, but the evolutionary pathways that produced them also were nearly the same.

This result fits awkwardly within the evolutionary framework. It also contradicts the results of the Long-term Experimental Evolution (LTEE) study, which demonstrated that microevolutionary biochemical changes are historically contingent. (To read an article I wrote about the historical contingency and the LTEE, go here.) The repeated discovery of convergence at the biological and biochemical levels in the face of the historically contingent nature of the evolutionary process makes me skeptical that biological evolution can explain life’s diversity.

And sorry, Saints fans, but the contingent nature of the NFL season makes me skeptical that the Saints can repeat.

Go Bengals!

  1. Federico G. Hoffmann et al., “Gene Cooption and Convergent Evolution of Oxygen Transport Hemoglobins in Jawed and Jawless Vertebrates,” Proceedings of the National Academy of Sciences, USA 107 (August 10, 2010): 14274–79.