Wednesday, August 14, 2013

The incredible story of bones


This article is inspired by Neil Shubin's book: Your inner fish. A highly recommended read!

Few are people who really understand evolution. Fewer still are people who know how bones appeared, despite how important bones are in our lives. We often think of our bones as as a part of our body that "protects" us, and that's true, but was it intended as a protection from the start? I think not! This story absolutely amazed me when I read about it and so I want to share it.

Once upon a time the oceans, hundreds of millions of years ago, all creatures were soft. The game of life with some of the protagonists eating each other was already going on, of course, but nobody was equipped with bones. It was all a world of flesh. Think of starfishes! They eat algae, decomposing matter of dead plants and animals that litter the ocean floor, and also snails and shellfish. Think of jellyfishes! They eat crustaceans, plankton, small fish.

Now, think of ancient prehistoric fish! When I tell you this, you'll think of fish as you know them! with teeth, fishbones, etc. That's not what I'm talking about. I'm talking about old fish. And by that I mean swimming animals that look a bit like sea cucumbers and worms. They were soft, which means they had a soft mouth and their preys sometimes escaped. And someday, thanks to a random mutation, one of them was born with teeth. All of its body was still soft, but it had teeth. And teeth in a soft fish-eat-fish world are a gigantic advantage. So, this fish thrived and it was then able to reproduce and have many children equipped with teeth who would also be as successful and have children of their own. With generations, they reproduced, their lineage ruled the seas, they ventured into new territories, adapted, and diversified into several separate species who would then consider each other as a potential meal.

And among the uncountable mutations that happen all the time, one of them proved again to be a game-changer. This mutation was responsible for grossly malformed teeth. These malformed teeth would become the backbone and would offer a resistance that flesh alone didn't have. It offered a chance of survival when being bitten. Different mutation, same story! If it offers an advantage, it increases the chances of surviving until reproduction and it will be passed on to further generations.

However, teeth are incredible things. They're the hardest part of our body, due to enamel. And that has a cost: the body has an economy of its own, based on the food it can get and the energy it needs to expend. The cost of maintaining enamel on bones was high while enamel was not necessary. Softer layers of the bones were hard enough to offer protection and had a lower evolutionary cost. This is why bones lost their enamel layer.

And one vertebra, one day, was malformed and enclosed the head. Thus came to be the skull. And with other mutations, duplication of genes or chromosomes, some new extra body parts appeared becoming fins. And about 700 million years ago, some fishes that were prey to others found safe harbor on land. This required adaptations for breathing, but they were able to temporarily escape their predators by climbing on land while their predators couldn't. As time passed, the evasive tactic became a lifestyle and fins turned to legs. The emblematic half-fish-half-reptile Tiktaalik would be the first conqueror of land that would give rise to reptiles, dinosaurs and other vertebrates like us humans.


As I recounted this story, I realized that I have forgotten many of its details and that I probably made a few mistakes (of little importance for my popularizing purposes). So I recommend you read Shubin's book or listen to the audiobook version of it. This journey through the evolution of our bodies is a fantastic one, and probably a little more accessible, because more focused on humans, than Richard Dawkins' The ancestor's tale.

I hope you enjoyed this short journey through evolutionary history and that it made you want to know more about it.

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