« Prev Next »
As a 9th grade student, one mandatory class that I take is biology. So far, I've learned a lot of fascinating concepts, but one concept that I found to be the most interesting is Natural Selection. Recently in biology class, we watched a documentary, and one thing that was mentioned was how, in the 1900s, mosquitoes adapted to DDT, which was an insecticide, after it was used for decades. I thought that it was so strange how an insect could adapt to a poison that is meant to kill it. Then, I realized that this was a prime example of natural selection. Natural selection, proposed by the legendary Charles Darwin, is the process in where certain mutations are chosen because they benefit the organism and help it survive to reproduce. This sparked curiosity in me, and as I did more research, I found a study that has been published last month explaining that evolution is happening very quickly right before our eyes; fish are adapting to PCBs found in the Hudson River at a speed that is faster than usual for evolution to take place.
So what exactly are PCBs?
PCBs, which stand for polychlorinated biphenyls, are organic chemicals that can be made by humans. They were used in many products, such as plastic and rubber, since they were good insulators, but in 1979 they were outlawed because they contained high levels of toxins and were proven to cause harmful effects on humans, such as cancer. They also can't break down easily, so that was another problem faced since they were emptied out into the environment and the oceans. As I mentioned in a previous post, Garbage Dump in the Middle of the Pacific Ocean, fish are ingesting the PCBs in the water, and this makes them become sick and die. If they survive, the PCBs make its way up the food chain, and eventually, we will be taking in PCBs from the fish we eat.
Since PCBs are harmful to animals, especially fish, one type of fish called the Atlantic tomcod needed to adapt to them or else they would die out. In order to meet their biological goal, which is to survive to reproduce, they needed to adapt and evolve their bodies to deal with the toxins in their environment. In order for evolution to take place, there needs to be a mutation, so there had to be a mutation in one fish which allowed it to cope with the PCBs. Since it was beneficial to the fish, it was passed down to offspring, and now, many fish carry these mutations in their genes which help them become immune to the harmful PCBs.
What is the mutation in the Atlantic tomcod that enables them to withstand PCBs?
After studying these fish for about four years, scientists have come to the conclusion that they have a modified gene which helps control the noxious consequences of PCBs. This gene is called aryl hydrocarbon receptor2 and it enables a fish to store the toxins from the PCBs as fat inside its body instead of getting deadly ill.
Even though this one species of fish is evolving to stay alive, there are still tens of thousands of fish left in the ocean that need to do the same. Our actions as humans, even though they might not be purposeful, has a big affect not only on sea life, but for many other land organisms as well .That is why we have to be responsible and take into consideration the affects of our behaviors before they are carried out.
Image Credit: Christoph_w via flickr
Referances:
Anne Minard "Hudson River Fish Evolve Toxic PCB Immunity" National Geographic February 17,2011
Janet Raloff "Packing away the poison" ScienceNews February 17, 2011
"Persistent Bioaccumulative and Toxic (PBT) Chemical Program" United States Environmental Protection Agency
"Polychlorinated Biphenyls (PCBs)" United States Environmental Protection Agency
