Evidence Of Evolution In The Human Body

The anatomical structure of the human body is a product of 3.5 billion years of evolution. There are anatomical features passed down through this process from lower animals such as fishes, sharks, amphibians and other animals. Some of these features are not as obvious as the opposable thumbs passed down to us from the lower primates. The features I am talking about are responsible for inconveniences such as, appendicitis, hiccups and hernias we experienced occasionally because the design of the human anatomy was shaped from anatomical structures of lower animals.

To get a better understanding of this we must look back at the history of these animals I just mentioned. It was Charles Darwin who first realized that all higher animals develop from embryos that look almost exactly like in the early stages of development and then later begin to look different as they develop because they are different animals. This observation was one of the first steps that lead Charles Darwin to develop the Theory of Evolution which has been proven in many branches of sciences such as genetics, pharmacology, biology, zoology and many more. Today it is no longer a theory based on hundred of proofs documented over the years. Back then Charles Darwin simply did not have the necessary scientific equipments and techniques such electron microscopes, PCR, electrophoresis, etc to prove it. You will be surprised what these evolutionary hand-me-downs are.

Hernias is a problem some boys and men experience from time to time due to the results of evolution. This problem ocurrs because the gonads, the ovaries in the females and the testes in the males, were not originally in there present positions in the body. Both the ovaries and the testes were originally located right next to the liver during the early stage of embryonic development.  They were located there because the liver and the gonads were probably intereacting with the same tissues in that area during the early stages of development. Sharks and other cold-bloodied bony fishes gonads are still located next to the liver in their body to keep them warm.

Humans on the other hand are warm-bloodied. The gonads in the male fetus gradually descends from the liver down into the scrotum to place them in a cooler area away from the body to keep them at an optimum temperature to maintain sperm quality.  But what happened during descension, the spermatic cord that serves as the conduit for the sperms, had to take a round about way to reach the testes in the scrotum. A loop was essentially formed. The spermatic cord had to enter the scrotum through an opening at the bottom of the pelvis and since the scrotum is an outpocket of the body wall this created a weakness in the wall that can lead to hernias, a protusion of the intestine. The gonads also descended in the female but close enough to the uterus so that the eggs would not have far to travel. Females in general do not suffer from hernias.

Hiccups is another annoyances we have that can be explain through evolution. It can last a few minutes, sometimes days or even for years. Hiccups is caused by a spasm of muscles in the throat and chest. This is an involuntary response which means we cannot control it. Hiccups are triggered when we eat too fast or eat too much and in some cases are caused by a tumor in the chest.

Hiccups occur because we inherited anatomical features from two different animals on the tree of life. The fish is one and the amphibian is the other. We inherited the major nerves that control our breathing from fish and the hiccup itself was inherited from the past we shared with tadpoles. There is a group of nerves called the “phrenic nerves” that innervates the diaphram. The problem is that these nerves originate from the base of the skull and have to go through a series of twists and turns to make their way through the chest cavity and eventually end in the diaphram just below the lungs. There are a few structures along the way that can press on these nerves and irritate them thus interfering with our ability to breathe. A hiccup is the end result of this irritation. A better design would have been for the nerves to originate from an area on the spinal cord much closer to the diaphram.

Unfortunately, we inherited this design from fish with their gills closer to the neck and as we develop into a fetus the location of the origin of the nerves does not change, therefore the nerves that used to travel a short distant to innervate the gills to control breathing in fish must now travel further since the diaphram is far removed from the neck.

The other reason we may have hiccups because we inherited it from the tadpole. Some animals start their lives in water such as amphibians, specifically tadpoles, breathe with gills and lungs. They are able to do this because they have the right muscular structures and placement of nerves to produce hiccups naturally. The tadpoles must take in water and push it out through their gills for oxygen but at the same time they must keep the water from entering their lungs. So how do they do this? They close the glottis, a flap of tissue over the opening to the lungs, to close off the breathing tube to the lung while they are drawing the water in to push it out through the gills. Basically, what they are doing is a prolonged hiccup. Ours is much shorter. By the way that same flap of tissue that close our bronchial tubes is called the epiglottis.

Many of us often have problems with our knees because after 3.5 billion years of evolution they still are not design correctly for upright walking. Remember animals use to be only in an aquatic environment such as oceans and streams for a while. The major bones in our legs, wrists and backbone were not designed to support a lot weight, especially with the high incident of obesity. They were really design for swimming. Orthopedic surgery for knee replacements is at all time high for people below the age of 50. This is why we experience a lot of torn cartilages and ligaments in our knees and ankles. Almost all form of animals that walk on land eventually experience some form of bone disorder because of this design of the joints. Aquatic animals did not used these bones to support a lot weight. They were used for locomotion in the their watery environment, not to walk around on two feet.

There are many modern day ailments we experience because of evolution. Many of these aliments ocurr in a few generations of the evolution process. For example,  the very well known aliment called sickle cell anemia, a blood condition where the shape of the red blood cells are changed from their normal double concave disc shape to a sickle shape. The gene that control the shape of the red blood cells was altered in response to an parasitic infection from malaria carrying mosquitoes. The shape of the red cells were change to confer an immunity to malaria in people who live mostly around the mediterrean region of the world. The parasites in the mosquitoes’ saliva does not thrive in people with sickle cell anemia. Unfortunately, the trade off in immunity leaves people with this condition with serious debilitating pains throughout their body. Fortunately, it takes two carriers of the defective gene to produce an offspring with this condition.

As you can see the process of evolution is not necessarily a process of improvement all the times as most people think it is. Sometimes traits that were good for other animals in the tree of life may not be a good attribute for animals higher up in tree such as us. Eventually in time, these annoyances such as hiccups, hernias, joint pains and many more I did not discussed here such as goose bumps, extra ear muscle, extra eye lid, the appendix, etc., may eventually disappear through the process of evolution and become a thing of the past.

References:

• Scientific American, January 2009, Volume 300, Number1, "This Old Body" by Neil H. Shubin
• Wikipedia

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