Explain why a person should believe that all life that currently exists on planet earth evolved from a simple, common ancestor through the process of mutation, natural selection, sexual selection and genetic drift.

In order to understand why many people believe that all life on Earth evolved from a common ancestor through various processes such as mutation, natural selection, sexual selection, and genetic drift, we need to delve into the scientific theory of evolution.

Firstly, it's important to note that evolution is supported by an extensive body of evidence gathered from various scientific fields, including paleontology, genetics, comparative anatomy, and molecular biology. These pieces of evidence allow scientists to construct a coherent and comprehensive understanding of how life has evolved over billions of years.

1. Fossil Record: The fossil record shows a progression of different life forms throughout Earth's history. Fossils provide evidence of organisms that existed in the past and demonstrate a gradual change in species over time. This supports the idea that common ancestors gave rise to diverse species.

2. Comparative Anatomy: Comparing the physical structures of different species provides compelling evidence for a shared common ancestor. For example, the skeletal structure of vertebrates exhibits striking similarities, suggesting a common origin. These similarities can be observed not only in overall body plans but also in detailed structures like limbs, organs, and bones.

3. Genetic Similarities: Advances in genetics have enabled scientists to analyze the DNA of various organisms. Comparing genetic sequences allows us to identify similarities and differences between species. Scientists have found remarkable genetic similarities between different organisms, indicating a shared genetic heritage. This supports the concept of a common ancestor from which all life descended.

4. Natural Selection: Natural selection is a fundamental mechanism of evolution proposed by Charles Darwin. It states that individuals with traits that confer a survival or reproductive advantage are more likely to pass those traits on to future generations. Over time, this results in the accumulation of favorable traits in a population, leading to adaptation and the formation of new species.

5. Sexual Selection: Sexual selection refers to the process by which certain traits are favored in mating, leading to reproductive success. Traits that are deemed attractive or advantageous by potential mates become more prevalent in a population over time. Examples include elaborate plumage in birds or antlers in deer, which are not directly related to survival but are favored during mate selection.

6. Genetic Drift: Genetic drift refers to the random variation in gene frequencies that occur in small populations over time. It can lead to the loss or fixation of certain alleles, which can affect the genetic diversity within a population. Genetic drift is particularly significant in smaller populations and can drive the formation of new species.

By considering these various lines of evidence, scientists have formulated the theory of evolution, which provides a comprehensive and well-supported explanation for the diversity of life we observe today. It is important to remember that the theory of evolution is continually refined as new evidence emerges, undergoing rigorous scientific scrutiny and testing.