Charles Darwin is widely regarded as one of the greatest scientists to have ever lived. He is credited with developing the theory of evolution by natural selection, which, although having undergone minor updates as new research is highlighted, is still the overriding theory behind the study of life sciences. Darwin’s theory of evolution by natural selection was a big idea that transformed how we view the world and our place in it, explaining, with one single idea, how all the myriad different living things on the planet came to be adapted so well to their particular environments.
But in coming up with his theory Darwin encountered numerous problems and obstacles, which his theory could not explain immediately. The biggest problem for Darwin and one used ever since he published his ideas by those opposed to his theory, is the ‘gap’ in evolutionary fossils, which Darwin relied upon to prove his theory and is commonly referred as Darwin’s Dilemma.
What is Darwin’s Dilemma?
Darwin's revolutionary theory of evolution, published 150 years ago, explained how natural selection picks out the genetic changes that are most helpful in fitting a species to survive. Put simply, evolution is the passing of genes from one generation to the next, with change.
However, those who argue against Darwin’s theories often point to the fact that Darwin failed to explain and account for the sudden appearance of large animal fossils more than 500 million years ago. It has been the greatest unsolved mystery in natural science ever since the publication of On the Origin of Species through Natural Selection in 1859.
Although highly contested by sceptics, in recent years, new scientific discoveries in the fields of geology and fossil records hint at an explanation. Scientists now believe that fossil records are actually a lot older than they originally thought, going back some 3,500 million years, an age more than seventy-five percent of the total of the planet itself. This extension of the planet’s age suggests that life-forms would have had time to evolve into the animals which then created the larger fossils.
Solving Darwin’s Dilemma: Is Oxygen the Answer?
The sudden appearance of large animal fossils more than 500 million years ago, bamboozling even someone with as lofty an intellect as Charles Darwin and giving rise to the term Darwin’s Dilemma, may have finally been solved.
In 2002, palaeontologist researchers from Queen’s University in Ontario, Canada, found the world’s oldest complex life forms. The life forms were found between layers of sandstone on the south eastern coast of Newfoundland, Canada and made scientists re-think their calculations for the age of complex life on Earth to more than 575 million years ago, closely linking it to the time massive ‘snowball’ glaciers that covered the Earth melted. The scientists argue that the melting of these massive glaciers created a sudden huge increase in the oxygen levels found in the world’s oceans and may be responsible for the rise in large animals on Earth after three billion years of mostly single-celled evolution.
The Canadian study showed that the oldest sediments on the area of Newfoundland that they studied completely lacked animal fossils and were deposited during a time when there was little or no free oxygen in the world’s oceans. However, immediately after this ice age there is evidence of an increase in atmospheric oxygen in the sea by as much as 15 per cent of modern levels, and the later fossils show evidence of larger animal fossils.
The study suggests then, that the injection of oxygen into the world’s oceans when the glaciers began to melt, kick-started a new phase in evolution – the leap to larger, more complex life forms, offering an explanation to Darwin’s Dilemma.
Darwin and the Eye
‘It is curious that I remember well time when the thought of the eye made me cold all over, but I have got over this stage of the complaint, and now small trifling particulars of structure often make me very uncomfortable. The sight of the peacock’s tail, whenever I gaze it, makes me sick!’ wrote Darwin in a letter when he was working on his theory of evolution.
Indeed, when those sceptical of Darwin’s theory of evolution want to criticise him, they often draw attention to the eye. Darwin himself said that he thought it was unlikely that the human eye evolved spontaneously. But in 2004, scientists at the European Molecular Biology Laboratory (EMBL) tackled Darwin's major challenge to explain the evolutionary origin of the human eye.
Studies of a "living fossil," taken from a marine worm that still resembles early life forms found on Earth up to 600 million years ago and known as Platynereis dumerilii, the researchers discovered that the light-sensitive cells of our eyes, known as the rods and cones, actually come from an ancient population of light-sensitive cells that were initially located in the brain.
Interestingly, scientists now know that humans have light-sensitive parts to their brains. The research argues that the human eye may have originated from light-sensitive cells in the brain and only later on in evolution would these brain cells moved away from the brain to create an eye capable of vision.
As Dr Eliot Marston (PhD in Childhood Leukaemia), Translational Research Manager in the College of Medical & Dental Sciences, University of Birmingham, UK, explains;
“Organisms without light-sensitivity develop a basic mechanism to detect it which makes them more suited to compete for resources in their environment, and mutations in subsequent generations gradually improve upon this in tiny increments over an extremely long time until you arrive at a functioning eye. It’s actually a very logical process following the theory of evolution.”
Modern Science and Evolution
New research is appearing all the time, particularly in the fields of genetics, to reveal the complexity and uniqueness of living things. Today, it is now known that all animals use the same core methods to grow into adults. Harvard Medical School's Marc W. Kirschner and John C. Gerhart, of the University of California–Berkeley show in their book The Plausibility of Life: Resolving Darwin's Dilemma, that living organisms and their 'parts' are very different from what we are used to seeing as parts for man-made machines. Instead, living organisms are able to make connections over and over again in order to make different functions.
For example, the scientists argue, while we may imagine that the processes involved in making the neck of a giraffe longer may be many-fold and include mutations such as expanding the neck muscles, or making the blood vessels longer, but infact, the scientists suggest, the muscle and blood vessels grow to fit around the bone. So what look like complicated biological mutations can actually occur without too complex a biological process taking place.