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  • 達爾文的演化遠征 DARWIN'S LOST VOYAGE

DARWIN'S DILEMMA

Darwin’s Dilemma

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.

DARWIN'S VOYAGES

Darwin’s Voyage of Discovery

To say that Darwin’s journey aboard the Beagle and time spent at sea was not life-changing would be an understatement. In 1831 – at the age of 22 – Charles Darwin was given the opportunity of travelling aboard a survey ship, HMS Beagle, as a naturalist. It was a round the world journey that took in several continents and equipped the young Darwin with a fundamental knowledge of geology and biology, as well as information on various animal species that would later prove extremely important when developing his theory of evolution.

‘The voyage of the Beagle has been by far the most important event in my life, and has determined my whole career. Everything about which I thought or read was made to bear directly on what I had seen or was likely to see; and this habit of mind was continued during the five years of the voyage. I feel sure that it was this training which has enabled me to do whatever I have done in science.’ - The life and letters of Charles Darwin, 1887

During his five year journey, Darwin filled countless note books and ledgers with an abundance of information and facts on the various animal and plant life that he picked up on his travels, shipping home more than 1,500 different species in the process.

Darwin was also able to make many important geological findings and notes on the effects of erosion, earthquakes and volcanoes. In an age when sea travel was both exciting, exotic and highly dangerous, sailing in a small Navy brig, the journey aboard the Beagle was a true voyage of discovery for the budding young naturalist, as he travelled from England to South America, into the Pacific Ocean and the Galapagos Islands, before returning via Australia, Mauritius and South Africa.

The Beagle & Journey

The Beagle was a Royal Navy brig just 27 metres (90 feet) long, yet it circumnavigated the world in just less than five years. On board were 74 people, countless provisions, supplies and 22 clocks, all stored in very small quarters.

The passage the Beagle took on leaving England was a popular route taken by ships in the nineteenth century. From England, the Beagle sailed south towards the Cape Verde Islands off Africa’s western coast, before heading West across the Atlantic to what is now Brazil. Moving down the coast the Beagle then surveyed the coast of modern day Argentina and the Falkland Islands before rounding Cape Horn – the southern tip of Latin America – and following the Pacific coast of Latin America north before reaching the Galapagos Islands. From the Galapagos, Darwin’s journey then took him right across the Pacific Ocean to Sydney, Australia, before moving onwards, once again, to Mauritius in the Indian Ocean and then Cape Town, South Africa. From Cape Town the Beagle then crossed the Atlantic once again, touching the Brazilian coast, before finally, after nearly five years at sea, making its way back to Britain. Although Darwin never stopped there – the place did not exist at the time of his journey - Darwin in north Australia was named after Charles Darwin by his former shipmate John Lort Stokes, who was on the Beagle’s next voyage.

Even today, a sea voyage of this length and distance would not be without risks, but it is worth remembering that Australia and much of the Pacific Islands, as well as New Zealand, were only discovered and accurately mapped by Captain Cook just over sixty years before Darwin undertook his journey. Sixty years on, there were still plenty of wild and unknown places for an enquiring naturalist to explore in the world.

South America

Although the Beagle and even Darwin to some extent are now inextricably linked with the Galapagos Islands in the Pacific Ocean, for most of the five year expedition the Beagle actually spent the majority of its time surveying the Southern Coast of what is today Argentina and Chile. It was in Latin America where Darwin made many of his most important discoveries that had a lasting influence on his future work and evolutionary theory.

In Brazil, Darwin first experienced the rainforest; collecting samples and making meticulous field notes to send back home. Further south, in what is now Argentina, and also on the bleakly desolate Falkland Islands, Darwin was able to find countless fossils and geological findings.

Later in the journey when the Beagle was surveying the coast of Chile, Darwin explored extensively Chiloé Island. After Tierra del Fuego, Chiloe is the largest island in South America. From north to south it measures 112 miles.

Interestingly, because of its geographical location and because the coastal mountains cross its entire length, Chiloé has two completely different environments. The Pacific facing side of the island is very damp with heavy rainfall and high winds to create an environment rich with vegetation. The continent facing side of the island is protected by the mountains and has a unique micro-climate that has supported native life for centuries. It was while exploring Chiloé Island that Darwin witnessed the volcanic eruption of Mount Osomo, something which increased his understanding of the earth’s geology.

The Galapagos Islands

Straddling the equator and approximately 600 miles to the West of the Latin American continent in the Pacific Ocean, the Galapagos archipelago has been described as one of the most unique, scientifically important, and biologically outstanding areas on the planet. Today, the Galapagos are a popular destination with naturalists and wildlife tourists. The Galapagos had a profound affect on Charles Darwin, where he was able to witness first hand the effects of evolution in isolation. Somewhat surprisingly however, on a journey that lasted nearly five years, many Darwin fans might be surprised to learn that the Beagle spent only five weeks on the Galapagos. Made up of lots of small islands, Darwin landed at only four of the islands on the archipelago: San Cristobal, Floreana, Santiago, and Isabela. It was the numerous differences between the animals, flora and fauna on each island that caused such a sensation to Darwin and helped him prove his theory. He wrote at the time ‘…the circumstance that several of the islands possess their own species of tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder.’
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