Final answer:
The Theory of Evolution by Natural Selection explains that individuals with favorable traits are more likely to survive and reproduce, leading to evolutionary change over generations. Variation within a population, competition for resources, and inheritance of advantageous traits are key factors in this process. Darwin coined the term 'descent with modification' to describe how species evolve and diversify over time.
Step-by-step explanation:
The theory of evolution by natural selection, put forward by Charles Darwin and Alfred Russel Wallace, is a foundational concept in biology. Natural selection, also known as "survival of the fittest," is the mechanism by which individuals with favorable traits are more likely to survive and reproduce, allowing those advantageous traits to be passed down to subsequent generations, leading to evolutionary changes. This process is contingent on the existence of variation within a population, competition for limited resources, and the inheritance of traits conducive to survival and reproduction.
Darwin's view was solidified by three principles: first, variation in traits among individuals; second, the production of more offspring than can survive; and third, the competition for limited resources. These principles undergird the concept that over generations, populations will evolve in a process Darwin termed "descent with modification." The theory states that over time, due to natural selection, species change and new species emerge, contributing to the diversity of life forms we see today.
The impact of natural selection is evident in the genetic variability of populations, which is due in part to mutations in the DNA, and the shifting nature of environmental conditions, causing those with favorable adaptations to thrive and, therefore, altering the genetic demographics of populations across generations. It is this mechanism of evolution by natural selection that helps to explain both the unity and the immense diversity of life we observe on Earth.