Tuesday, March 31, 2009

Engineering Aquamen? It's harder than you might think.

Stephen Cass at Science Not Fiction recently tackled the question "could genetic mutation or manipulation create a superhuman?". The answer, not too surprisingly, is maybe - it all depends on what kind of superpower you have in mind. Flying? Probably not. A fluorescent glow? Almost certainly.

One of the examples of genetic engineering that Stephen writes about piqued my interest: a team of scientists at the MRC in Cambridge were able to modify human hemoglobin so that its biochemical properties were more like crocodile hemoglobin. Could that give a human Aquaman-like powers?

First a little background. Hemoglobin is the protein in our red blood cells that carries oxygen. One of its properties is that it binds oxygen more strongly when carbon dioxide levels in the blood are are low (such as in the blood vessels in the lungs). Higher levels of carbon dioxide - produced as waste when oxygen is used by cells to generate energy - reduce the affinity, promoting the release of oxygen from the hemoglobin. The exact biochemistry of the protein varies from species to species, depending on the animal's physiological needs and the environment it lives in.

Crocodile hemoglobin, for example, is more sensitive than the human version to dissolved carbon dioxide in the blood. The result is that a greater proportion of the hemoglobin bound oxygen can be released when the crocs are holding their breath, which allows them to stay under water for as long as an hour. It turns out that changing just a few amino acids in the human hemoglobin sequence changes its biochemistry to that of the crocodilian version. This recombinant "scuba" hemoglobin was developed as an improvement to artificial blood products, and was only produced in bacterial cells. But imagine introducing such a modified hemoglobin sequence into a human - it would potentially allow the carrier to hold their breath for an hour, just like crocs.

But unless such engineered Aquaman wannabes want to spend their time in warm shallow water lurking for their prey evildoers, they would need a number of other modifications to reach their superhero potential. Besides stay under water a long time1, Aquaman is also supposed to be able to dive very deep in the ocean and swim very fast. Neither ability is going to be provided by modifying hemoglobin.

The problem is that both the intense cold and high pressure in the ocean depths can easily kill any ordinary human. Animals that do routinely dive to great depths - like sperm whales - built anatomically to survive the pressure changes: they lack sinuses, have special structures in their ears and reinforced airways. There is no way to create similar changes in human anatomy without multiple genetic alterations. Whales also have a nice layer of blubber that acts as insulation. The blubber also makes the whale's body more buoyant and streamlined, which are important for rapid swimming.

Possibly a human could be modified to live like a whale, but he would end up looking pretty whale-like. In other words, he'd look like the big guy in the picture below, rather than the slim muscular dude wearing little more than tights.
The idea that genetic engineering could easily be used to reconfigure the human body to give it extraordinary abilities (for a human anyway), while retaining a normal human shape is a pet peeve of mine. If you are talking about biological beings, rather than magical ones, function does affect form.

1. I know Aquaman is supposed to be able to extract oxygen from the water in some kind of gill-less fashion. I'm not even sure where to begin to tackle that one.

Image (top): Cover of Aquaman 17 at comics.org
Image (middle): Structure of hemoglobin of the antarctic fish Pagothenia bernacchii. DOI 10.2210/pdb1hbh/pdb .
Image (bottom): Aquaman fights a whale guy in a panel from JLA #223 at The Aquaman Shrine.

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1 comment:

Arvind Mishra said...

Lots have been said about the human species being aquatic sometime in his long evolutinary history ! He may be now able to relive his past ! Thanks to technology and human ingenuity !