Evolution is a theory that explains how life on Earth has diversified into millions of different species. It is a key principle of biology and it connects and explains many facets of life. The theory of evolution states that the diverse array of organisms on Earth has evolved from a single common ancestor over time. Evolution works through a process known as natural selection.

Natural selection makes it more likely for the best-adapted individuals to survive and reproduce. Individuals who reproduce pass their traits on to their children. The children with the traits that are best adapted to survive are more likely to pass their traits on to the next generation.

Over multiple generations, the traits that offer the best chance of survival and reproduction spread across an entire population. In different environments, different adaptations are beneficial for survival. Over time, the organisms in different environments begin to evolve into different species because different adaptations are being selected for by natural selection.

For example, on land animals often have long, thin limbs to help them move around. In water, however, limbs are not very helpful and animals are usually nicely streamlined and have short flattened fins. Evolution addresses many aspects of life on Earth.

The theory of evolution can help us to answer important questions such as:

  • Why do so many different species exist on Earth?
  • Why do different regions have unique species?
  • How come different species can seem so similar?
  • Why do different species have unique adaptations?
  • And why do different species that live in similar habitats have similar adaptations?

Natural selection

Natural selection is the process that drives the evolution of new species. It is based around the concept that individuals with beneficial traits for in their environment are more likely to reproduce and pass on their traits and genes to more offspring.

An organism’s environment is shaped by a range of factors such as temperature, precipitation, wind, predation, competition, and disease. As environmental factors change, the level of benefit gained from certain genes and traits varies. Some genes and traits become more beneficial in a specific environment while others lose their benefit.

New species emerge through natural selection in different environments over many generations. This is because individuals with traits that are more beneficial are more likely to survive and reproduce. These beneficial traits are then passed to the next generation. Different beneficial traits are passed from generation to generation in different environments and, over many generations, the populations in different environments become very different from one another.  

For example, the photos above show two different colored moths in two completely different environments. One environment is filled with green leaves while the other is a desert made from orange sand.

In the green, leafy environment the orange moths stand out while the green moths are very difficult to see (they’re there, I promise). In this green, leafy environment it is much more likely that predators will spot, catch and eat the orange moths. The green moths are much more likely to go unnoticed, survive and reproduce. In this environment, being green is an advantage and a beneficial trait.

In the desert environment, the green moths stick out against the orange sand. In this environment, the orange moths have a much better camouflage and would be less likely to be eaten by predators and more likely to reproduce.

If a single species of moth lived in both of these environments, over time, natural selection would change the two populations in different ways. The population of moths living in the green, leafy environment would be more likely to gradually become green while the population of moths living in the desert would be more likely to become orange. Over many generations, two new species would have evolved through natural selection.

Charles Darwin

Charles Darwin is arguably the most significant biologist of all-time due to his work on the theory of evolution and the mechanism of natural selection.

Darwin’s publication ‘On the origin of species by means of natural selection’ changed society’s perception on the natural history of Earth. It delivered a solid argument for the theory of evolution and provided a plausible mechanism – natural selection – that could lead to the evolution of new species.

Nearly 150 years have passed since Darwin first published his theory and the quantity of evidence to support his work is staggering. Subsequently, much of the present-day biological research is performed with the theory of evolution as its foundation.

In 1859, Charles Darwin presented a publication titled ‘On the Origin of Species by Means of Natural Selection’. Thirty years of research and thought were collaborated into the publication that changed our understanding of the natural world.

The book presented two arguments backed up with large amounts of evidence from nature. The first point proposed that species were not created in their current forms but evolved from common ancestors. The second proposed the mechanism that pushed the evolution of species – natural selection.

When Darwin presented his paper, creationism was the dominant belief amongst the general public and the scientific community. Naturally, there was great resistance to the theory of evolution as it contradicted the words of the ‘Old Testament’ and flipped the common view of how life had developed.

Darwin wasn’t the first to write about evolution but he was the first to propose the theory with enough evidence and logic for the world to take notice and effectively changed western culture and the study of life, forever. Darwin’s development of the evolutionary theory did not come out of the blue but was a product of the combination of similar geological theories, diligent observation and clear reasoning.

George Cuvier, a pioneer of palaeontology (the study of fossils), observed and documented the change in fossil records from older to younger rock. He also noticed that younger fossils bared a greater resemblance to present-day species than older fossils. However, Cuvier was a fierce opponent of the theory of evolution and explained the changes in time by a theory of catastrophism.

Last edited: 20 October 2020

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