Evolution of life
Depicting the evolution of life on Earth. Earth (upper left) was born from clouds of gas and dust surrounding the Sun, which in turn was born from gas which condensed in our galaxy (upper right). Once the Earth started to cool after its formation, oceans formed, which were teeming with the basic chemical building blocks of life. From these components, first unicellular, then multi–cellular organisms evolved. As time progressed, larger predatory animals evolved, such as cartilaginous fish like the shark (center). These, and the bony fish (lower frame) which evolved later, paved the way for the conquest of the land.
Evolution is a process that results in changes in the genetic content of a population over time. Evolution describes changes in inherited traits of populations through successive generations. In fact, when we talk about evolutionary inheritance, the latter is what we are actually referring to: the transfer of genetic sequences from one generation to the next. When particular genetic sequences change in a population (e.g., via mutation) and these changes are inherited across successive generations, this is the stuff of evolution.
The study of evolution can be performed on different scales : Microevolution and macroevolution. Microevolution reflects changes in DNA sequences and allele frequencies within a species over time. These changes may be due to mutations, which can introduce new alleles into a population.
In contrast with microevolution, macroevolution reflects large– scale changes at the species level, which result from the accumulation of numerous small changes on the microevolutionary scale. An example of macroevolution is the evolution of a new species. Macroevolution, on the other hand, refers to change at or above the level of the species.
Thus, evolution reflects the adaptations of organisms to their changing environments and can result in altered genes, novel traits, and new species. Evolutionary processes depend on both changes in genetic variability and changes in allele frequencies over time.