The Basics: Evolution by means of Natural Selection
In the minds of most people Evolution and Charles Darwin will forever go hand in hand, and quite right too, he came up with the idea of evolution by means of natural selection. However, he did not come up with the idea of evolution itself. A prime example of this is Erasmus Darwin, Charles Darwin’s grandfather, he had the words E conchis omnia emblazoned on to the side of his carriage beneath the family crest of three seashells, it means ‘Everything from seashells’. Over the years many people grappled with the problem of evolution including Gregor Mendel with his pea experiment, Hugo de Vries with his evening primrose mutations and Charles Darwin with his finches and their bill shapes. This leads us to the two main questions of this article – What do we mean by evolution? And what did Darwin bring to the table?
What is Evolution?
The idea of evolution is that life changes over time. This is the opposite of Intelligent Design, the idea that everything in the world was created, yes things live and die, but the replacement is the same within certain variation. Evolution rejects this steady state principle and embraces the fluctuation within species as signs of continued adaptation. This is a struggle that is seen all over the world that gives rise to new species.
Theory of Evolution by means of Natural Selection
So what was Darwin radical new idea? Natural Selection.
The principle of Natural Selection is very simple. It is based on two things, firstly, the ability to survive and reproduce is down to more than random chance, and secondly, that this advantage could be passed on to the next generation. Today we would understand this as an advantage based on genetics but back then they did not know about DNA.
Survival
Now let us explore the first one, the ability to survive and reproduce, this is called an organism’s fitness. If we imagine a wolf pack chasing down a herd of deer, which deer do they single out? Is it the one in the back? The one that made a miss-step? Perhaps the sick or elderly one? So they have the option of the slower runner, the least agile, the most susceptible to illness or the oldest. Through this analogy it is easy to see how prey and predator get locked into an evolutionary battle of speed, agility and health. But this does not explain why deer grow antlers, or the difference between the markings on male and female birds.
Reproduction
It can often be observed that a female bird is well camouflaged whilst the male has clearly dressed for the occasion. The array of colourings and patterns that males show is really astounding but surely makes them more obvious, more likely to be eaten by a predator, thereby reducing their ability to survive and reproduce. This is where reproduction comes in, mate selection. Without considering behavioural patterns a female invests more in the next generation. The energy investment to produce an egg is greater than that of sperm. This leads to an imbalance, generally females will have one clutch, litter or offspring each season whereas a male has to potential to have many more. Therefore, females tend to be more selective while males compete for attention. This leads to a variety of different ways they show their superior genes. A brightly coloured male will have to be faster and more agile than his dull counterpart to avoid predation. This can lead to males getting brighter and brighter, or their tails getting more and more ornate as is the case with the peacock. Therefore, fitness incorporates both the ability of an organism to survive and produce offspring.
Inheritance
The second part relies on heritability, the major reason that evolution works, the ability for the trait which made the parent successful to be inherited by the offspring. Today we know about DNA and genes so I will used them to help illustrate the concept. There are two copies of a gene within each cell. When organisms reproduce sexually, one copy from each parent is passed down to the offspring. Now this offspring will not necessarily gain the same advantage that the parent had as this is now a new combination of genes but it is easy to see that within families people tend to look similar but not identical.
Summary
Evolution can be used to describe the interplay between predator and prey, organism and environment. It is the process that gives rise to variation with a population and thereby producing new species. It was Darwin’s biggest accomplishment, describing the process that drove evolution> His theory of evolution by means of natural selection combines these different forces into one theory. This theory now underpins work within the field of evolutionary biology, with terms such as fitness, mate selection and heritable traits regularly being used.
Further Reading
Natural History Museum – What is Natural Selection
A more detailed look the driving forces behind natural selection, including a look at Darwin’s famous finches, the inspiration for his evolutionary theory .
National Geographic – Natural Selection
A short article that covers natural selection but it also includes a glossary of terms.
Learn more from The Basics range
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A brief overview of how DNA works as the mechanism through heritable traits are passed down.
Most DNA is translated into proteins, but what exactly is a protein?
How to change DNA, this molecule that underpins how traits are inherited, and why would we want to.
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