We have detected that you do not have the latest version of Flash player installed.
Please click here to download the Flash plugin

If you do not wish to download the latest version of Flash player please click here to bypass detection.

Loads of time for Charles Darwin

It is 200 years since the birth of one of Britain’s greatest scientists. Charles Darwin was born on 12th of February 1809, and his theory of evolution has proved to be one of the greatest ideas of science.

What is Darwin’s theory?

Darwin said that evolution was driven by a process called 'natural selection'.


So what is natural selection?

The recipe goes like this:

Organisms always show some variation

For example, a species of millipede can be red or black.

All organisms are subject to environmental stress

Not all of the millipedes will live to their natural life span. Most of them will be eaten! If birds tend to spot the red millipedes more easily than the black ones, more of the red millipedes will be eaten. Less red millipedes = more black millipedes that survive and reproduce.

Millipedes

They show heredity

The surviving black millipedes tend to have black babies because this trait is genetically present.

The end product

The more advantageous trait, that is, being black, allows the black millipede to have more offspring. These offspring will show the black trait. After enough generations, the whole population turns black!

Bingo, evolution!

As environmental pressures change, different traits become more or less advantageous. This means that new species are always produced to take advantage of changing conditions. For example, if the climate warms up, species that can cope with higher temperatures survive and reproduce. Eventually new species evolve that thrive in warm weather!

What does it all mean?

Natural selection means that species and organisms best suited to their environment are more likely to survive and reproduce. They then pass on the characteristics which helped them survive to their offspring.

Gradually, species change over time. Many thinkers of the period were working towards this idea, but Darwin was the first person to put all the pieces of the puzzle together and write it all down. The full title of the book is ‘On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life’. It is still worth a read today. The basic ideas underlying evolution are very simple and covered in every biology classroom in the country.

The hominoids are descendants of a common ancestor

So, what took so long?

One really interesting question is why it took so long for people to work it out. The main reason is time. Darwin was probably one of the very first people to realise just how much of it there is. Up until Darwin most people assumed the Earth was about 6000 years old. Back then this was calculated by looking at the events in the bible and working backwards.

There are at least 50 million species on Earth. It’s seems impossible that that they could all have evolved over 6000 years, a relatively short period of time. Many thousands of species would have had to evolve every day. For his theory to work, Darwin needed time, and lots of it!

Some clues: volcanoes, earthquakes and great landscapes!

Landscapes Volcanoes and Earth Quakes

Darwin made many groundbreaking observations. He was one of the first people to appreciate that landscapes change over time. Mountains grew slowly and were equally slowly eroded away by the weather. He had seen volcanoes erupting and had experienced an earthquake where he saw some of the ground pushed upwards. He knew that to produce landscapes as varied as he had seen all over the world, trillions of tones of rock needed to be eroded away, transported and re-deposited. This all needed huge amounts of time.

Working out the age of the Earth

The first really scientific approach to working out the age of the Earth was done by Lord Kelvin. He knew a great deal about heat energy. He realised that the Earth must be losing heat to space and therefore cooling down. He estimated the maximum temperature at the centre of the Earth could have started off at about 3872 °C (7000 °F).

He could calculate the rate at which the Earth was losing heat by looking at the change in temperature of rocks: about 17°C (63°F) per 50 feet of depth. He calculated that the Earth was about 100 million years old. Not old enough for Darwin and the geologists, and too old for the bible!

What Kelvin didn’t know was that the core of the Earth is highly radioactive. This provides lots of energy to keep the Earth hot for a very long time. Modern estimates put the age of the Earth at around 4,500 million years. Lots of time for evolution and everything else!

Surviving the extremities!

Darwin got a good grip on how life evolves and changes, but we are still making discoveries about how good life is at surviving. It seems that once life has got started it really hangs on. Almost everywhere we look we find it! From the deepest darkest mine shaft, the bottom of steaming oil wells, under the surface of freezing rocks in Antarctica, lounging around inside boiling pools of salty water in Yellow Stone Park, and even basking in tanks of nuclear waste!

Thermophiles

Extremophiles

These organisms are called extremophiles, because they can live in such extreme conditions. They are usually bacteria. There are lots of different types:

Acidophiles

These can live in very acidic conditions. The most extreme can thrive in a pH of 0. That’s stronger than battery acid! Some like it hot!

Hyperthermophyles

These can survive very high temperatures. Some live in temperatures of over 120 °C (248 °F). This is hotter than most pressure cookers and way above the normal boiling point of water. If a human being was exposed to such temperatures for even a fraction of a second, he or she would definitely get third degree burns.

These creatures live around hydrothermal vents on the sea floor. Here hot water gushes out of undersea volcanoes at up to 4000 °C (7232 °F). The microbes that thrive in these conditions never see sunlight, they are around about 3Km (1.8 miles) and so cannot use photosynthesis to make their food. They live directly off the minerals dissolved in the hot water.

Whole colonies of more complex organisms like the tube worms in the picture live off the extremophiles. More and more species of these are being discovered all the time and they look as if they could have been very important in getting life started in the first place. In the early history of the Earth such conditions would be common. So just maybe we all owe our existence to a few bugs living on some very unfriendly real estate in the depths of the oceans.

ET takes a bath

Europa

In fact we may have some neighbours in our solar system that live in similar conditions. Jupiter’s moon ‘Europa’ has an ocean of water covering its surface.

The top layers are frozen and look just like the ice sheets covering the Antarctic ocean on the Earth. Down below it is liquid, and it probably has hydrothermal vents!

Could there be life down there? It is a real possibility. The National Aeronautics and Space Administration (NASA) has plans to send a robot spacecraft to find out.

ALVIN and SENTRY

It would not be a simple mission. First it would have to penetrate the ice. It could do this by carrying a small hot nuclear reactor to melt its way through. Once through, it would have to swim around in total darkness under its own control looking for life. It would need to be a pretty smart machine. NASA is supporting projects to develop just such a robot.

Sentry is an Autonomous Underwater Vehicle (AUV) swimming around looking for new hydrothermal vents on the Earth. One day, a descendant may be swimming around the oceans of Europa!

The big questions:

How does evolution produce intelligence? Is it really a big survival advantage?

Are human beings the ultimate extremophiles because we can survive in the depths of space, the Antarctic wastes, or nuclear waste sites?

Computers are often said to be ‘evolving’ at an enormous rate. Do you think the next life form we see on earth will be based on Silicon instead of Carbon?