Evolution is one of the most widely known scientific theories, at least on the surface level. You’re reading this article right now thanks to the result of millions of years of evolution to produce a creature with the intelligence and reasoning skills to understand complex language and concepts.
We have evolution to thank for every achievement and success of the human race, but how much do most of us really understand the theory of evolution? If you want be more clued up on the famous theory of evolution introduced to the world by Charles Darwin, read on.
Genes, Recombination and Mutation
Firstly it’s important to know that every part of all the physical characteristics of creature – size, colour, appearance – is decided by its DNA. DNA (DeoxyriboNucleic Acid) is the blueprint for life and contains all the instructions to make a living creature: every living creature is a result of its DNA.
Another characteristic every living thing shares is the ability to reproduce: creating copies of themselves with slight differences. Billions of years ago when life on Earth was just forming, this was restricted to single-cell organisms dividing themselves into perfect copies, sharing the exact same DNA – most of the time anyway, but we’ll get to that in a moment.
Of course, Earth is now teeming with tens of thousands of varied and complex lifeforms which reproduce by mating: a male and a female combining their cells together to form new offspring.
Living creatures produce reproductive cells known as gametes, sperm cells for males and egg cells for females. These cells are created by copying half of the DNA of the creature, which is selected randomly. When two creatures mate and the male inseminates the female, an offspring with half the DNA from each parent is formed. The two pairs of DNA are combined randomly to produce a child with a mix of traits from both parents. This is all well and good but you may have picked up on something: the recombination process – both as individual gametes and during fertilisation – can’t actually create anything new.
This is where mutation comes in.
Sometimes during the process of copying the DNA into the gamete, a copying error will occur and the resulting gamete will be slightly different from the original DNA – a mutation has occurred. Mutations are often negative and affect the creature adversely, but sometimes they are neutral or even positive changes. The blue eye colour in humans is one example of such a mutation.
During fertilisation, If one of the gametes contained mutated DNA, then the child will have some traits which belonged to neither parent, but this mutation is now part of its DNA and there is a chance it will pass this trait onto its children.
So we know that evolution occurs via the changes to DNA through the two natural processes of recombination and mutation. However, there is still a problem. All of these processes are random. How can all the amazing, complex lifeforms we see today on Earth be so perfectly adapted to their environment if they all merely the results of random chance. Well, there’s one more crucial piece of the puzzle we’ve still yet to talk about. Perhaps you’ve heard of it:
With all the randomness involved in determining the DNA of new offspring, there are billions of possible different DNA combinations any one creature could have. The important thing is however, these random variations are not created equal and some will of these offspring will have a natural advantage over others in its environment due to the traits it has inherited. The offspring gifted with longer legs will be more able to chase down prey and run away from predators, the ones with skin colourations that blend into their environment will escape the notice of unwary predators or prey. Because of the advantages certain individuals of a species possess, it is much more likely they will survive and pass on their genes than the ones who do not possess these natural advantages. As such, over time the localised gene pool of the species will predominant with the traits most beneficial to group.
Factors in natural selection include predators, diseases, rivals of the same species, shortage of food, changes in habitat and climate. Whenever something changes in the environment that a creature habitats, those with the traits best suited for that environment will be the ones to reproduce until the species has transformed to be suited to that habitat as a whole.
Natural selection examples in effect include:
- Certain giraffes having longer necks than others allowed them to reach food in higher trees, allowing those giraffes to survive in greater numbers and passing on the genes determining their long necks.
- There are many examples of animals with colourations that match their surroundings escaping the notice of predators and eventually all members of that species
- Insects and Parasites are notorious for their ability to become resistant to the man-made chemicals designed to kill them, having gained immunity to such chemicals within a matter of just months. It is even known for species of insects to have been immune to insecticides within a single generation.
- Flowers with larger and more colourful petals are more easily noticed by bees, making it more likely they will be visited and pollinated by one. Similarly, male peacocks with larger and more colourful plumages are more impressive to a mate, and thus they will be the ones to mate and pass on their genes.
- Perhaps the most famous example is that of a group of finches on the Galapagos Islands, off the shore of South America. The Galapagos Islands was not the usual habitat for the finches – it is believed a large storm must have blown them there – and as such was rife with food and no predators to harass the finches. The finches population exploded across these islands until rivalries became fierce. However, some of the finches found themselves an ecological niche – an opportunity only they could exploit – because their beaks. Some of the finches possessed long, thin beaks well suited to digging for worms, whilst others had thick, wide beaks better suited for cracking open nuts and seeds. The finches begin to mate only with other finches in the same group as them and as such, the characteristics of their differing beaks became enhanced to further improve their efficiency at finding food. Eventually, the two groups of finches had changed so much they could no longer mate with each other – they are now two completely separate species.
That’s all well and good, but thus far we’ve only covered micro-evolution – changes in a single species over a relatively short period of time.
But you’ve likely heard of theories of whales having evolved from land-based mammals over a course of millions of years. And perhaps you’ve heard tales of the humble chicken being one of the closest relatives to the T-Rex? How are such drastic transformations possible?
The answer is macro-evolution. Macroevolution isn’t any more complex than microevolution at its core; the exact same principles apply, simply with the causes and effects extrapolated over a much longer period of time. Billions of years ago, amphibian-like creatures with the best traits to survive on land slowly evolved into the reptiles we now know as dinosaurs. Unlike the Darwin Finches and other examples mentioned previously however, this transformation took millions of years as opposed to merely hundreds.
Similarly, later mammals returned to an aquatic lifestyle, with the best traits being selected over and over again in a course of millions of years until they became whales. Whales are indeed mammals and still share many of the traits commonly associated with land-dwelling mammals such as feeding giving live birth as opposed to laying eggs, feeding their young on milk, breath air with two lungs through their blowholes, which are believed to have adapted from the nostrils traditionally found on land-dwelling creatures. A look at the skeleton of a whale will even show they possess underdeveloped hip and leg bones within them that go unused, a leftover artefact from their ancestors.
So to recap, evolution is the changes of traits within animals through generations caused by the random mixing of DNA when gametes are produced and when the egg is fertilised. Then, the likelihood of each individual surviving it’s based on how suited to the environment their physical characteristics and traits are, meaning the best adapted creatures are the ones who will pass on their genes and eventually the species will be perfectly adapted to its environment. Whenever there has been so much chance in their genetic code that the creature cannot mate those it once could, a new species has officially been formed. Stretch this process over millions of years and there can be some drastic changes, such as the evolution of land mammals into whales.
Alternate Theories Of Evolution To Darwin's Theory of Evolution
This is evolution as we understand it today, built upon the concepts and theories proposed by Charles Darwin. However, Darwin’s theory of evolution wasn’t the first or only one to have been considered and analysed by the scientific community.
The most well known theory of evolution besides Darwin’s belongs to that of Jean-Baptiste Lamarck. Lamarck’s theory was centred around the idea of use and misuse. Lamarck proposed that a feature of an animal became bigger and stronger the more the creature used that characteristic, with the traits the creature doesn’t use growing weaker and disappearing eventually. Believing in a form of memory shared through ancestors (Now often called genetic memory) Lamarck also theorised that the repeated use of a trait would be recorded and that record would be passed onto its child, emphasising that trait and allowing the child to possess a stronger version of it before ever using it. For an example of this, whereas Darwin later theorised that Giraffes with long necks were simply more likely to survive and pass on their traits to their children, Lamarck believed that the Giraffe’s neck grew longer over its lifetime through repeated use and the Giraffe would pass on the memories of that use to its child, ensuring it had a longer neck than its parent.
Lamarck’s theory of use and misuse and acquired characteristics was later discredited as our increased understanding of genetics showed these ideas have little grounding in reality, whereas as Darwin’s ideas of evolution have been shown to have much more merit on a wide field of scientific subjects.
But Isn’t Evolution Just a Theory?
But – some might ask – isn’t evolution just a theory, still unproven? With many competing theories of evolution (Charles Darwin’s and Jean-Baptiste Lamarck’s simply being the best known) and Darwin himself having made many inaccurate statements and guesses regarding his theory, do we really have any reason to believe evolution is real?
The first of these doubts often arises from the name: the theory of evolution. If it’s only a theory, doesn’t that mean it hasn’t been proven?
In the world of science, a theory means something a little different from its everyday usage. In science, a theory is a conclusion based upon the available facts and observable data – and when new data comes to light, a new conclusion might be reached. A theory does not remain stagnant.
Darwin’s theory itself has grown and matured thanks to the contributions of scientists who came after him. Darwin himself did not know about genetics – it wasn’t until about a century later until DNA and genetics became understood. But Darwin made some observations about the natural world in regards to how living things are perfectly suited to their environment and how offspring inherit traits from their parents, and attempted to reason why nature worked like this, even if he couldn’t fully appreciate the underlying mechanisms of what he was trying to explain. When Darwin’s The Origin Of Species was written, it was a hypothesis – a reasonable and well-thought out conclusion based on the available evidence, but one that still has room for doubt and error.
Now Darwin’s hypothesis is supported by a wide body of evidence from the fields of palaeontology, geology, genetics, biology and more. It has enough evidence behind it is proven beyond a reasonable doubt to be an accurate representation of the reality of how things work in nature and is thus the Theory Of Evolution.
Like its subject matter, Darwin’s hypothesis has evolved from a controversial book which drew heavy fire into one of the most respected and influential theories across many separate fields of study. Much like the still unfinished journey life has taken to reach this point, the Theory of Evolution will continue to adapt and change as even more discoveries refine it. Where our understanding of evolution will go no-one knows for certain, but whatever we learn we will be all the more stronger and more adaptable for it.
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