Evolutionary Essay

Caryn Bradshaw

 Biology

3^rd hour

Evolution Essay

“Change is at the very core of evolution and without it, all creatures would look alike and behave the same way.” -Martin Dansky-

          Things are growing and changing around us everyday. Creatures big and small all over the world posses their own unique characteristics, but when you get to the bottom of things, every living, breathing, organism is made up in the same way.  So you would ask, if we are all made up the same way, then how are we so diverse?  There is no simple answer, but there is a theory.  This theory has grown over the years and is still studied today; it is the Theory of Evolution.  The definition of evolution is a change in the lines of decent of living creatures over time.  This means that it is believed new species develop from earlier species as a result of molecular changes.  Now, this theory is commonly perceived as scientists trying to explain the origin of life.  However, it is simply an explanation as to how organisms formed after life was created.  In addition, evolution is not something that just occurred in the past.  It is happening right at this moment and will continue to happen for eternity!  Included in this paper is information on the early theories of evolution, examples of microevolution occurring, and evidence of the theory of macroevolution.  Also included will be my personal opinion on the most convincing evidence of evolution.

            In the 18^th century, comparative morphology became a study among scientists.  Comparative morphology is the systematic study of similarities and differences in body plans between major groups.  Studying this requires taking a closer look at bone structures and physical appearances of life forms.  This study brought about a question in scientists minds.  How can animals appear different in bodily features, but so much alike in others?  An example of a study performed to look at comparative morphology would be to compare the pelvic structure of a manatee.  Now, for a sea manatee, there would be no need for a pelvic structure because they don’t walk.  However, scientists have found that sea manatees do in fact have a ghost socket where a pelvic structure would be found.  Why is this?  There were intermediate fossils found that gave evidence to there being such a thing as a “land manatee.”  These fossils contained many of the same characteristics of sea manatees, but included pelvic structure meaning they were able to walk.  How is this possible?

            A well-respected anatomist, Georges Cuvier, was first to come up with the theory of Catastrophism.  This theory suggested that at one point in time, there was a universal catastrophe that destroyed many of the life forms on the planet.  Then the survivors repopulated the world.  Cuvier stated that the offspring of those species were not new, but were just ones that scientists had not found fossils of yet dating clear back to the time of creation. 

            Some people were able to accept Cuvier’s theory, but others, like a man named Jean Lamarck, set out to prove the theory wrong.  He knew that inheritance of characteristics had something to do with the way species grew and changed.  So he hypothesized that environmental pressures and needs bring about permanent changes in animals and their offspring.  For example, if a species of giraffes have a short neck and are unable to reach high branches for food, they simply stretch out their necks to reach it.  By stretching out their necks day after day for food, the giraffe develops a long neck.  Once the long neck is developed, the giraffe passes the characteristic on to its offspring.  Although Lamarck’s theory is not necessarily reasonable, he was right with the fact that the environment plays a role in evolution.

            In the 1800’s, a geologist by the name of Charles Lyell began contradicting Lamarck’s theories.  He spent his time examining sedimentary rock layers and their age.  While many scientists suggested the earth was about 6,000 years old, Lyell came to the conclusion that the earth had to be millions of years old.  He came about this conclusion because there were so many rock layers that is was impossible for them to all form in the short period of time of 6,000 years.  This became known as the Theory of Uniformity.  After taking an even closer look at the rock layers, it was also understood that the possibility that a catastrophe occurred was nearly impossible. 

            In the middle of all of these forming theories about evolution came a man who would truly influence the way everyone viewed evolution.  In 1831, Charles Darwin embarked on a voyage across the sea to South America where he studied the diverse life on all the different islands.  Marine life was also part of his collection. 

            When Darwin returned to England, he began to review his notes and drawings of his findings.  He noticed that he had discovered some fossils of extinct animals, but then saw that some of the new species he examined resembled the extinct animals!  As he looked through his drawings and notes, he observed that not all of the species were alike, but they did show variation in size, color, and many other traits.  By reviewing all of his findings, Darwin was able to combine his new theories with those of Lyell and other scientists.  He was then able to formulate a theory that included all of the evidence found.  Variation became a huge part of Darwin’s conclusion because variation would enable the species to survive and reproduce in certain environments.  In other words, he proposed that an environment would “select” specific characteristics for a species to possess.  This is now called natural selection.  For example, if a finch lives on an island where their only food source is hard-shelled seeds, they must have a strong beak to crack the seeds open.  However, there are a few finches that lack a strong beak and have a lesser chance of survival.  Therefore, the strong beaked finches have a better chance of surviving and reproducing.  Over time, the strong beaked finches become abundant and the population of finches will be mostly strong beaked finches.  With that information you can conclude that a population is evolving if inheritable traits continue to change over time.

            Since Darwin’s theory emerged, variations in traits have been shown to be controlled by genes in DNA.  Microevolution occurs when little changes in allele frequencies are brought about by mutation of genes, genetic drift, migration, and natural selection.  When mutation in genes occurs, the result is a change in the DNA structure, which is heritable.  This occurrence is the source for diversity in species and organisms.  Gene flow and genetic drift is also a contribution to the diversity of things, but is can only cause a change in existing allele frequencies.  When alleles leave or enter a population, as a result of immigration or emigration, it is called gene flow.  This idea is much like genetic drift, however, genetic drift is brought about by chance only.  This size of a population affects the diversity of genetic drift because of the fact that small populations are more likely to loose alleles completely.

            An example of microevolution could be the guppy computer activity we did in class.  Imagine that there are all kinds of different colored guppies; some bright, some semi-bright, and some dull.  They all live in the same pond and share the same predators.  Because the brightly colored guppies attract the predators, they are eaten and unable to reproduce further.  However, the dull colored fish and even a few semi-bright guppies are less attractive and don’t get eaten as much, so they go on to survive and the population of them increases.  Now in another pond, the guppies share their habitat with fewer predators.  Since female guppies prefer to mate with brightly colored guppies, the dull colored ones are unable to mate enough to keep their population up.  So in the second pond, unlike the first pond, the brightly colored guppies make up most of the population.  As a conclusion, you can see how microevolution plays into the survival of different species.  The simplest factor in a population can play the biggest role in how an environment thrives. 

             Macroevolution is large-scale patterns, trends, and rates at a broader view.  Some examples of this broader study are fossil records, comparative morphology, and biochemistry.  However, most would say the most recognizable forms of evidence of macroevolution would be fossils.  Scientists use sedimentary rock sequences as geological time scales to define eras and eons.  Comparative morphology uses fossils as well as existing life to form similarities that show evolutionary relationships among groups.  Taking it a step further would be the use of biochemistry.  This is where scientists identify differences and similarities between species on a molecular level.  They can look at how one strand of DNA pairs with another strand from a different species and form an idea of the evolutionary distance between the two tested. 

            Out of everything I have discussed, I feel that the most convincing evidence is the study of macroevolution.  Those scientists are able to look at geological evidence, morphology, and DNA structures.  All of these things put together in my opinion are the keys to life and evolution.  You are able to look at time and age first, then you can see different structures of species and compare them to modern day species, and to take it a step further, you are able to look at DNA structures between species.  As Martin Dansky stated, “Change is at the very core of evolution and without it, all creatures would look alike and behave the same way.”  I feel this quote sums up my discussion on evolution.  We are all basically the same, and therefore we must have come from one common ancestor.  Everything in life has a cause; it’s just a matter of finding that definite reason for existence.