The theory of evolution is the foundation of biology. Currently we have technology that allows us to decipher the DNA code, which guides the species classification in modern taxonomy. However, the theory of evolution was proposed long before the existence of this technology and was accepted as a scientific theory based on concrete evidence.
Learn the difference between a normal theory and scientific theory.
Darwin proposed that the characteristics of the species are changing slowly through the generations due to the pressures of their environment, these changes constitute evolution. The following evidence supports the theory of evolution
The fossils provide much information on the living things that existed in the past. Bones, teeth, fingerprints and even whole organisms are preserved million years. Currently we have technologies such as carbon-14 dating allows us to determine the age of fossils. The analysis of all fossil creates a complex description of how living things have been changing over time. For example, in the fossil record we can see the transition from fish to amphibious in Class Sarcopterygii with lobe-finned fish and lungfish.
Some parts of the body of an organism no longer have any function, but left over from an older form of the organism evolutionarily. These parts are called vestigial structures. Over time, the body’s needs change and sometimes accumulates other adaptations which function having the structure originally. As evolution is a slow and continuous process, a vestigial structure no longer function, but it has not completely disappeared. Examples include the coccyx and the appendix of the human being. The coccyx is the last part of the spine that at some point served to hold a queue that no longer have. The appendix is what remains of a digestive organ (as a second stomach) we no longer need. It is assumed that over time these vestigial structures disappear from the human body.
Some plants and animals have similar structures that perform the same function despite not having a close genetic relationship. These are called analogous structures and support the theory of evolution because they show that species adapt to their environment over time according to the limitations and resources of their environment. For example, dolphins are closest relatives of humans than sharks. However, dolphins and sharks are very similar in shape and body size, color, location of the fins, etc. This is because the characteristics of the natural environment sharing (the water pressure, the sea depth, the refraction of light in water, etc.). The adaptation process resulting in the analogous structures and bodies with the same shape is called convergent evolution. Examples include the shape of the leaves of aloe and agave (the penque), and the wings of insects, birds and bats that make flight possible.
Different organisms that first glance do not seem in the least share structures that show their true relationship. For example, birds, bats, horses, dolphins and humans all have digital bones (fingers) and you can see how these same bones were changed to develop different forms which are the wings, hooves, fins and hands as the development of each organism in the tree of life.