What is evolution? Evolution is the development of life on earth. This is a process that began billions of years ago and is still continuing to this day. Evolution explains to us how it was possible for the enormous diversity of life to develop. It shows us how primitive protozoa could become the millions of different species that we see today. Evolution is the answer to the question that we have all asked: how is it possible for ancestors to have descendants that are so different to them, or how can one animal turn into a whole new species of animal? A species is a community of animals that is capable of producing offspring with one another, with the offspring also being able to reproduce. To answer this question, we will follow the life of a single celled eukaryote, named Barry, as he changes through time and eventually develops into an animal we see today. Being able to understand why an organism will change from its current state and develop is key to explaining evolution. This paper aims to answer this question by explaining how interactions within a biological ecosystem, the flow of energy and matter, changes in genetic information, structure and function, and emergent properties contribute to the evolution of single celled eukaryote to a multicellular animal roaming the earth today. Life is tough and when it comes down to it, everyone is looking out for themselves. Biology is essentially about reproduction and trying not to die, and both of these things are very difficult because of competition. There is a finite amount of resources on the planet so evolution drives us to compete for them in order to survive long enough to spread genes all over the place. Competition is a really important part to how different species interact when their habitats overlap. From all the forms of competition, the most prevalent to evolution is the predator versus prey relationship. For thousands of years, humans were preyed on not only by bears and wolves, but also by viruses, bacteria, and parasites. Predation doesn’t only occur between animal and animal. What is most important about predation, is the evolutionary pressures that come with hunting and being hunted for thousands of years. Because of these pressures, predation has driven all sorts of amazing adaptations that are seen everywhere. From grizzly bears having enormous claws and teeth, to the wolves concept of hunting in packs, as well as humans developing medical supplies to combat illness. In the end the effect of predator and prey interaction is an evolutionary arms race that results in the massive amount of diversity we see in any ecosystem. It’s been going on since the Cambrian Explosion, more than 500,000 years ago, and it will continue to spawn bursts of diversity forever. Everyone tends to think of predation as wolves killing sheep, or hawks hunting mice; however, predation is much more than carnivores killing and eating, it applies to any type of interaction where one organism kills another for its energy. A lot of evolution comes down to the flow of energy through nature. Every living thing needs energy to meet its evolutionary goals of staying alive and reproducing. Predators kill because they are hungry, but they are hungry because they need energy to survive and reproduce. Almost all energy on earth starts with plants. For example, a cow eats grass to capture their energy. It may not seem like predation; however it is an organism eating another organism in order to consume the energy from the sun. Predators and prey have millions of years of tricks stored in their DNA because every organism is playing to the same set of evolutionary rules, whether a lion, or cow, or bacteria, gaining energy efficiently (without being eaten in the process) is essential to reproductive success. The constant need to survive allows organisms to develop weapons or defense mechanisms in a never ending evolutionary arms race; predators develop sharp teeth and keen eyes, while prey develop camouflage or escaping techniques to outmaneuver a predator.