How Evolution is Still Making a Difference
Off the coast of Ecuador, on the Galapagos Islands, an important scientific discovery occurred. Charles Darwin noticed birds on different islands that looked very similar but with one key difference, their beaks. Since he didn't know much about birds, Darwin took samples back to England to consult an ornithologist, a person who studies birds. The ornithologist confirmed that though these birds were similar, they represented different species. This example of speciation, where a new variety of bird is formed due to evolution, can be explained by looking at their food sources.
On each of the Galapagos Islands Darwin studied, a different food source was available to the birds. Some birds ate seeds, others ate insects and others found leaves and flowers for food. These food sources acted as selective pressures. If a bird built with a beak for eating seeds lived in a place that only had insects available for eating, the bird would starve and never reproduce. Therefore, birds with beaks meant for seed eating could never survive in a place with only insects. Biologists would say the bird with a beak for seeds was not fit for an environment with insects. This concept is also described as survival of the fittest or natural selection. Selective pressures force a species, in this case birds, to adapt or die.
How Organisms Get Different Traits
Every biology student must memorize this:
DNA -------------> RNA ----------> Proteins
Biologists use the term, the central dogma, to describe the process of making proteins and it explains how life happens. Every living thing needs proteins. Proteins give structure, carry signals, make up organs and in general allow us to carry on with our lives. As the central dogma shows, DNA becomes RNA through a process called transcription. RNA then becomes proteins in a process called translation. Any new trait in a species comes from a mutation in either DNA or RNA. The imperfect DNA replication process makes mistakes and this causes mutations. Different types of mutations alter the DNA code which produces proteins, which alter the traits of an organism. Mutations do not always cause an organism to develop a beneficial trait. In fact, many DNA mutations cause genetic disorders or cancer.
A new trait requires that a mutation takes place. Then the environment must select for a trait by allowing organisms with that trait to survive. Even though Darwin’s bird beak discovery happened a long time ago, scientists still try to understand the complexities of evolution and our DNA.
Adaptation in our world today
Spend any amount of time in the healthcare world and you’ll hear about antibiotic resistance, and for a good reason. In recent years, germs that cause illness have evolved an ability to survive the antibiotics that used to kill them. What happened to the birds’ beaks, happened to the bacteria that makes us sick. In this case, the antibiotics created a selective pressure. For example, a particular colony of bacteria that enters a person's body may make them sick. The person receives an antibiotic which kills almost of the bacteria. However, a small amount remain with a trait that allowed them to live. In the case of the birds, this trait was the beak that allowed them to eat. Bacteria notoriously reproduce quickly and soon that small amount could grow and make the person sick again. Whenever antibiotics are prescribed the pharmacist will tell the patient to take all of the pills. Signs in hospitals often explain that even though a person feels better, disease-causing bacteria might still live in their body so every dose of antibiotic must be taken to kill those bacteria!
Bacteria have a superpower called lateral gene transfer. Vertical gene transfer occurs when a species has offspring and gives some of their genes to the next generation. Lateral, or horizontal, gene transfer occurs when two bacteria cells temporarily join and exchange their DNA, or genes. Here is why that matters. If an ill patient stops taking their antibiotics before they were supposed too, some of the bacteria left in their body could be resistant and some of the bacteria might not be resistant. However, using lateral gene transfer the resistant bacteria can give their resistant DNA to the other bacteria, allowing them to survive and come roaring back stronger. Then the whole colony of bacteria will have adapted. This time the ill person has to take a stronger antibiotic to kill off the bacteria. Stronger antibiotics often have worse side-effects on the person and eventually, even the strongest medicines will not kill the super-powered bacteria. One particularly bad bacteria is C. Difficile which kills about 15,000 people per year.
The Peppered Moth in England provides another example of evolution in real time. Usually Peppered Moths display white wings with black spots. This pattern allows them to blend in with tree lichens and avoid predators that eat them. This changed in the nineteenth century when industrial factories pumped soot into the air and the soot colored the tree trunks, and other surfaces, black. A genetic variation of the Peppered Moth had almost entirely black wings. Previously, this black-winged Peppered Moth was more obvious to predators and it was rare to find. However, once black soot started covering surfaces, the black-winged Peppered Moth blended in more efficiently than the white-winged Peppered Moth. In 1848, the first black-winged Peppered Moth was documented. By 1895, 98% of Peppered Moths living in cities were black-winged. The population transformed again later when air quality improved. Without black sooted surfaces, the black winged Peppered Moth lost its evolutionary advantage and the white-winged Peppered Moth increased.
Neat stuff, right?
Evolution impacts every facet of life. If you think this is neat and want to study biology in college, check out Upchieve’s academic coaches. They can de-stress the college search.