Scientific theory, not frivolous fiction

A scientific theory is a set of carefully made observations and events based upon proven scientific hypotheses. It is not merely a made up explanation. It is based on evidence that is collected by scientists, based on scientific laws, and is subjected to peer review by other scientists. Ideas are tweaked and honed but never entirely replaced. Once a scientific theory is accepted as truth, it can be used to make predictions of future events. Scientific theories are much more complex than scientific laws, and most scientific theories will never become laws because of their inherent complexities.

Scientific theories include plate tectonics, cell theory, atomic theory and the theory of relativity. All of these are supported by incredibly strong evidence and, along with evolution, have never been disproved. No theory, however, provokes as much controversy as evolution.

Origin of a controversy The evolution theory is mainly credited to Charles Darwin. In the early 1800s, at the tender age of 22, Darwin embarked on a five-year voyage around the world on a ship called the HMS Beagle. This journey led him to the Galapagos Islands, off the western coast of Ecuador in South America, where he collected specimens of finches, tortoises, worms and barnacles, and many animals from other places.

On his return journey, Darwin continued to study finches. He wondered how these birds came to be, and why various species were subtly different on every island, yet strikingly similar in ways to other birds on the islands and mainland.

Darwin wondered if the island finches shared a common ancestor with mainland finches. He knew that species compete for natural resources and potential mates, and considered if this was the driving force that led some individuals within a species to successfully breed, or for others to breed at a lesser rate. He called his theory Natural Selection.

It was later coined as Survival of the Fittest by Herbert Spencer - who also promoted Social Darwinism. As Darwin's theory became more and more widely accepted, scientists naturally began asking about the origin of human beings and how we might have evolved over the years.

Nosing your niche, naturally

There are two forces that drive evolution. The first is natural selection, which suggests that all living organisms are in competition with each other and with other species. Plants compete for light, space, water and nutrients. Animals compete for food, space, mates, dominance and other things. The results of the competition determine whether the organism successfully breeds, and therefore passes its genes on to the next generation or not.

If you are faster, bigger, more attractive, or smarter - or have any other particular trait that makes you better than others within your species - you will be among the fittest and will therefore get more chances to breed. This will enable your genes to have an influence on future generations. In contrast, you will have fewer chances to breed if you lack such qualities. The end result of natural selection is that favorable traits are passed on while less favorable traits die out.

In the case of Darwin's finches (he observed at least 13 species), he concluded that mainland finches are ancestors of various island finches. Although the birds are similar in size, shape and color; their beaks vary greatly. The finches on the Galapagos Islands developed different types of beaks to enable them to successfully exploit the various habitats and food sources. Finches that ate nuts naturally needed bigger and stronger beaks to crack the shells. Other finches developed specialized beaks to to feed on nectar or insects, or to drink the blood of seabirds.

Since the different feeding methods require specialized beaks, the animals' genetics adapted to the needs and eventually evolved the right tool for the job.

Swimming in the gene pool

The creation of a new species is called speciation. It takes a very long time for speciation to occur. Adaptations are seen in just a few generations, but it can take millions of years for DNA to differ sufficiently to result in speciation.

Since no two species of organisms can exist in the exact same niche, geographical isolation by rivers, mountains, canyons or islands - aids a species in exploiting its niche. The isolated groups breed within nearby groups.

Nature will evolve a species so that it might take advantage of a new niche. This inevitably leads to certain genes prevailing in one population and other genes prevailing in another population. This is called genetic drift.

Visible differences can be quickly observed in a selective breeding program, which combines desirable traits during breeding with other selected traits. Dogs are a good example. There is a wide variety of dogs, from the tiny Chihuahua to the enormous Great Dane. Yet the common ancestor of all dogs is the Gray Wolf.

Selective breeding helps to shape physiological and behavioral differences. Selective breeding is also common among thousands of ``modified'' plants and other organisms deemed by man to be helpful to humans.

The right stuff

The second driving factor of evolution is sexual selection, which governs behavior or physical attributes helpful in attracting mates, as opposed to aiding survival. Some traits in birds, reptiles, fish and mammal have evolved to quickly display to the females of the species just how good the males' genes are.

Song, color, large antlers, mating rituals and other ``sexy'' features are used to sexually attract a mate. Favorable traits suggest to females that some males' genes are better than others for her offspring.

An example is the colorful plumage of a peacock's train (tail feathers). The train is a major hindrance to the male's survival, as it slows its escape if attacked, rendering it vulnerable to predators. But it is most advantageous during the mating ritual, when the males parade their fancy plumage to attract females. The female subconsciously recognizes that he is fit enough to survive and has the ``right stuff'' (good genes) to pass on to her offspring.

Mutation

Genetic mutation can occur within DNA, such as during the formation of sex cells. This is known as meiosis. This can produce organisms with slightly different traits. Often these mutations amount to nothing, and other times they have negative impacts on individuals. But if they happen to benefit the organism by producing larger muscle mass, longer necks, longer tongues, brighter petals, or tastier fruits, the organism may breed more successfully. Then the mutated DNA will pass to the offspring and the successful mutation may spread through the population and eventually lead to speciation.

Evolution uses its many instruments - natural selection, sexual selection, geographical isolation, genetic mutation, adaptation, competition, sexual reproduction, and genetic drift - to create a climax of beautiful and incredible diversity among all life on Earth.

David Canavan has an MSc in Behavioral Ecology and teaches science, math and ICT at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind; the more dangerous the better. You may contact David at davidc@gardenbangkok.com .