Darwin’s Missing Puzzle Pieces
Charles Darwin truly was insightful to come up with the theory of evolution through natural selection, particularly during his time. Not only did he challenge religious thought of his day (that man was created by God in his own perfect unchanging image), but he proposed this theory even when many pieces of his evolutionary puzzle were missing. Puzzle Piece A: For example, Darwin was missing information on the mechanism of evolution. How did creatures carry information from one generation to the next? Back in Darwin’s day, most people (including Darwin) accepted the “BlendingTheory” which stated that offspring were a blend (and therefore intermediate) of their parents. If this was the true mechanism behind inheritance, eventually everyone would look the same and all individuality would be “blended out.” We know today that this is not correct, and in fact the system is much more complicated. Unbeknownst to Darwin, the concept of genes and genetics came from Gregor Mendel’s sweet pea research, which was conducted in the late 1800s. Mendel unknowingly discovered the true inheritance of traits through genes and chromosomes, and his research inadvertently would kick off the entire field of Saylor URL: www.saylor.org/bio102
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genetics. However, even after his work was published, it would lay dormant in the literature for 20 years until it was rediscovered by Hugo de Vries, Carl Correns, and Erich von Tschermak. Even after this rediscovery, and despite the obvious link between Darwin’s ideas and Mendel’s work, the connection between them would not be made until the 1960s during a period called the “Modern Synthesis.” The Modern Synthesis involved the reconciliation of Mendel’s genetics work with Darwin’s evolutionary ideas. Soon after this union, a scientific explosion led to the evolution of several new fields of science including ecological genetics, evolutionary genetics, microevolution, macroevolution, and population genetics. Puzzle Piece B: A second piece that was missing from Darwin’s picture was the true age of the earth. According to the Bible, God had created the earth in 4004BC. Charles Lyell, a good friend of Darwin, along with several other geologists, felt the earth was in fact much older. Darwin felt an older earth was more likely, since his ideas of evolution would require much more time to give the modern diversity of organisms. Darwin estimated the planet to be several hundred million years old (NOVA 2007). It wouldn’t be until the discovery of radioactivity, by Marie and Pierre Curie, that a real estimate of the earth would be calculated. Radioactivity would soon be used to date the oldest rocks on earth, which were found to be between 4.1 and 4.2 billion years old. Some feel that the true age of the earth is even older based on meteors that were believed to have formed at the same time. The most recent estimate of the Saylor URL: www.saylor.org/bio102
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earth’s true age is 4.5 billion years old, which would give plenty of time for Darwin’s evolution to take place (NOVA 2007). Puzzle Piece C: The fossil record contains gaps, which would eventually be filled in by new discoveries of transitional fossils. The fossil record is incredibly incomplete for many reasons. First of all, the right conditions suitable for fossilization are incredibly rare. For traditional rock fossils, the organism must die and not decompose or be eaten by scavengers. Then, the organism must be immediately buried in anoxic conditions (no oxygen). Even if an organism gets quickly buried under the right conditions, over time heat and pressure must be applied to convert the organic matter to rock. Even under these “perfect” fossil conditions, fossils must then be rediscovered through the process of erosion. In addition to these rare conditions, tectonic activity has a way of destroying many of these buried treasures. Plate subduction (whereby one tectonic plate slides under another) can cause the destruction and remelting of many valuable fossils. Finally, the fossil record can be quite biased in what does get preserved based on the nature of the process of fossilization. For example, you will find many examples of ocean life such as clams, trilobites, and sea coral. Sedimentation can happen rapidly in aquatic environments and many of these organisms have hard parts that are easily Saylor URL: www.saylor.org/bio102
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preserved as fossils. However, based on their habitat, some organisms are rarely preserved. For example, organisms that live on the top of a mountain are much less likely to be preserved, particularly if they have soft bodies and few hard parts. Activity—Putting Together Your Own Puzzle: Now that we have discussed some of the limitations of the fossil record, it is time for you to put together your own puzzle of evolutionary history. Pick a time period that you are interested in and create a list of organisms that existed during that time. Use the fossil record, scientific literature, and any other reliable resources that give you the information you need. (Reliable resources include government websites, peer-reviewed journals, university websites, and other solid sources). For your time period, create a list (and pictures when possible) of plants, animals, and insects that existed (if they were around during your chosen time). Create a document that lists the information on the organisms you find and then when images are available use them to create a collage of existing organisms for your time. This should give you a good idea of life for the particular time period you have chosen. This exercise should also make you realize the limitations of the fossil record. What do you think is missing? What do you have an overabundance of? To get started, visit the website below: http://www.ucmp.berkeley.edu/help/timeform.php Images Used: http://commons.wikimedia.org/wiki/File:Jigsaw.png http://commons.wikimedia.org/wiki/File:The_Blue_Marble.jpg http://commons.wikimedia.org/wiki/File:Agaricocrinus_americanus _Carboniferous _Indiana.jpg Saylor URL: www.saylor.org/bio102
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