The article is dubbed "similarities in the embryonic development of various animal species are also found at the molecular level." Scientists such as Karl von Baer, Ernst Haeckel, and Charles Darwin have done a tremendous job in assessing the various developmental similarities that exist in embryos of different organisms. Scientists today have also proven that these similarities are not only found at the phenotypic but also at the molecular levels. In an experiment carried out in the 19th century, evidence showed striking similarities in the appearance of the embryos from different species of animals. As such, the three aforementioned scientists came up with the hypothesis that the individual development of an organism fundamentally mirrors its phylogeny or evolutionary history. Thanks to molecular biology, evidence has shown that such similarities also occur at the molecular level through gene expression. Consider a fish, fly, or a crocodile; there is a particular stage within their developmental cycle that the embryos of these organisms are difficult to distinguish phenotypically (Max-Planck-Gesellschaft, 2010).
Researchers have also unfolded that the similarities mostly occur during the middle stages of the embryo development at a period known as the phylotypic stage. Many species-specific variations mostly happen either before or after this stage. Researchers have referred to this as the hourglass model. The waist of the hourglass reflects the morphological similarities witnessed amongst these organisms. Research today has however increasingly focused on the similarities at the most basic level which is at the molecular or cellular level (Max-Planck-Gesellschaft, 2010). As a result, there is a body of research that continues to draw a strong relationship between ontogeny and phylogeny. Gene expression also follows the hourglass model previously discussed. During the stage of morphological similarities, gene expression also shows a typical pattern amongst different organisms. However, once the organisms pass through this development stage, variations reoccur. Therefore, in essence, these studies have aimed at drawing the linkage between evolution and development at the molecular level.
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Several theories have been fronted in a bid to explain the developmental similarities witnessed in the middle of the embryo development. For instance, a researcher at Dresden known as Casey Bergmann noted that the similarities could be as a result of selection. One of the organisms that have been extensively used in this research is the fruit fly. It has enabled the scientists to study the similarities and variations at the molecular level mainly. Therefore, it is important to appreciate that the hourglass phenomenon has provided scientists to track back in history where the developmental variations began. Scientists hope to find answers to the critical questions on the etiology of the many variations seen in the animal kingdom. The zebrafish has also provided scientists with a valuable tool to assess the morphological and molecular variation that occurs during the developmental stages of the embryo.
The article does a significant role in proving that indeed living organisms show development at different stages in their lifetimes. Development can either be at the physical or phenotypic level or the molecular level. The article attempts to draw a relationship between evolution and development of an organism. The hourglass phenomenon explains that within the development of an embryo, there is a stage where embryo of each species resembles each other phenotypically. Research has further shown that such similarities are seen at the molecular level. Therefore, from this, it is important to conclude that living organisms have an evolutionary relationship witnessed during development. Researchers are however keen to trace the origin of the differences and further assess why they diminish at this point in the middle of the embryonic development.
Reference
Max-Planck-Gesellschaft. (2010, December 15). Similarities in the embryonic development of various animal species are also found at the molecular level. ScienceDaily . Retrieved September 24, 2018, from: www.sciencedaily.com/releases/2010/12/101215112815.htm
