Where did the first cell come from?
Over the years, scientific materials have stated that living cells came from a single cell. The question that follows is where did this single cell come from? There has never been a single agreed answer to this question because for anything to exist, according to the theories of evolution and mutation there should be a cell involved. The statement means that the first single cell, therefore, must have come from another cell if science is anything to go by (NCBI, 2012) . Several assumptions exist trying to suggest where the first form of a living cel l came from which are as illustrated.
The original molecule that formed the first living cell might have been different from the one existing today while the energy molecules happened to exist in abundance. Secondly, it is a possibility that chemical compositions of the earth at that time was very conducive to the production of protein chains leading to the oceans being filled with random protein chains mixed with random enzymes (NCBI, 2012) . There might have been a random chemical reaction and process that created this cell. Suggestions also exist that the first cell was just something different from DNA. All these examples suggest the origin of the first living cell but they are not suggesting how life came into existence from them. This subject can also be argued from the religious point of view through relating the creation of the first living cell to a supernatural being such as God or any other that exists depending on one’s religion.
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Viral Eukaryogenesis theory
Viral Eukaryogenesis theory is controversial too in a number of ways. The theory suggests that “the cell nucleus of eukaryotic life forms evolved from a large DNA virus in a form of endosymbiosis within a methanogenic archaeon” (Bell, 2001) . Understanding the origin of these cells is still not easy as some researchers state that the first member was a multimember consortium that consisted of several viral ancestors of nucleus, an archaeal ancestor belonging to the eukaryotic cytoplasm combined with a bacterial member from the mitochondria (Bell, 2001) .
It is suggested that a cell wall that was less archaeon and some alpha-pro-bacterium made up a type of relationship that led to the making of a complex DNA that later produced 3 organic materials which evolved to make the eukaryotic cell (Bell, 2001) . Subsequently, the methods in which the virus replicated and produced daughter cells probably led to the evolution of both asexual and sexual mitotic replication cycle. Additionally, it is proposed that several characteristics that are found in the eukaryotic nucleus are directly derived from the cells viral ancestry; these include mRNA capping and the linear chromosomes (Bell, 2001) . Other suggestions are that phagocytosis evolution that took place from the co-evolution with nucleus led to eukaryotes to exist as the first organisms to occupy its predator niche.
Douglas Theobald’s Test
Douglas Theobald’s did a number of research works and test that he posted in different journals and periodicals with regards to the UCA. He claims in the report that the tests he has carried out are real “without any assumptions that sequence similarity implies genetic kinship” (Theobald, 2011) . His tests involve trying to identify whether common unguided ancestry for a group of similar genes is more likely compared to independent ancestry that is unguided for similar genes (Theobald, 2011) . An example of this would be a convergent evolution case. He states that sequence similarity is capable of arising from many different factors other than just the common ancestry due to factors such as structural constraints, biases in mutation or even artifact manufacture.
The theory on this topic is that the probability of highly similar DNA sequences coming out of independent evolutionary processes is almost zero (Theobald, 2011) . This explanation, therefore, means that the only possibility is that these sequences must have just been inherited from some common universal ancestors. He further suggests that there is no equivalence between sequence similarity and homology just because sequence similarity involves real empirical observation while homology is a mere hypothesis used to explain the concept of similarity.
Common descent theory
Common descent theory is used within evolutionary biology to refer to the common ancestry that a particular group of organisms has (Keynes, 1998) . The theory involves the idea that new species of an organism are formed from an earlier ancestral population. The evolution that comes from universal common ancestry is directly related to common descent as it involved a number of speciation events between species from natural selection and geographical distinction (Keynes, 1998) . This theory, therefore, suggests that every single living organism in the world is a descent of a single ancestor, thus the reason as to why species in different parts of the world, geographically separated exhibit different traits. Common descent is basically derived from physical observation of various phenotypes (Keynes, 1998) . Changes in DNA of organisms still suggest a shared ancestry amongst organisms.
Bibliography
Bell, P. (2001). Viral eukaryogenesis: was the ancestor of the nucleus a complex DNA virus? Journal of molecular evolution , 3 (53), 251-256.
Keynes, R. (1998). Theory of common descent. Exobiology: Matter, Energy, and Information in the Origin and Evolution of Life in the Universe (pp. 35-49). Cambridge: Kluwer Academic Publishers.
NCBI. (2012). The origin and evolution of cells . Retrieved 4 27, 2018, from NCBI: https://www.ncbi.nlm.nih.gov/books/NBK9841/
Theobald, D. (2011). On universal common ancestry, sequence similarity and phylogenic structure. Brandels University, Biochemistry department. Waltham: Biomed central.
