LIFE
1802--William Paley published a forcefully argued treatise entitled:Natural Theology - or Evidences of the Existence and Attributes of the Deity Collected from the Appearances of Nature.
This is perhaps the best-known work that uses the Argument from Design to argue for the existence of a creator.
Argument from Design: Living systems are so exactingly well-adapted to their purpose, and so incredibly complex, that they could not have arisen by chance. Indeed, they appear to have been designed by a supremely competent designer. Since living systems could not have arisen by chance and appear to have been designed then surely they must have been designed.For example, the haemoglobin molecule consists of 4 chains of amino acids twisted together. Each chain contains 146 amino acids. Life on Earth is based on 20 different kinds of amino acid. Therefore, the number of different ways of making a chain of 146 amino acids from 20 different building blocks is 20 multiplied by itself 146 times, since at each position in the chain one can place any one of 20 amino acids. That number is 20146 or about 10190 !
Even if random combinations of 146 amino acids were put together at the rate of one trillion a second, it would still take about one million times the age of the universe to have a fair chance of creating a single haemoglobin molecule by chance alone! Clearly, chance alone cannot lead to life.
The Argument from Design seems, in view of these odds, utterly compelling. However, fifty years after Paley's book a purely natural way to achieve adapted complexity was discovered.
1859--Charles Darwin published Origin of Species. This is arguably the most revolutionary work in the history of science. It is certainly the most controversial. Darwin's basic idea is very simple; so simple, in fact, that it is frequently misunderstood. He recognized a purely natural way to obtain highly adapted complex organisms:
complexity can arise as a result of the cumulative effect of small random mutations.
adaptation to a particular purpose is the result of a selection effect: mutations that confer advantage to an organism enhance the chance that the organism will survive long enough to reproduce. If the organism reproduces it will pass on the mutation to the next generation.If, however, a mutation reduces the chance of survival then that mutation is less likely to be passed on to the next generation because the organism may perish before it reproduces.
Thus over many generations the survivors will be those organisms that are best able to survive. These are the organisms that are best adapted to their local environment. This selection effect is called
Natural Selection
as opposed to
Artificial Selection,
which humans have been practicing on lower animals for thousands of years, and may well be on the threshold of practicing on themselves.
It is important to understand that, unlike evolution by artificial selection, evolution by natural selection, is undirected and goal-free. There is no aim, no master-plan, no built-in tendency towards perfection: what survives is what works best at the moment.If big brains are currently a good thing, then big-brained creatures will succeed until big brains are no longer an asset. From this perspective, making big-brained creatures called homo sapiens is no more a goal than making eboli viruses.
We, like eboli, are just twigs on an expansive tree of life. We think we are important only because we can, whereas eboli cannot!
If evolution by natural selection has occurred on Earth, can it occur, and has it occurred elsewhere?
Our galaxy contains about 100 billion stars; the known universe contains about as many galaxies. Given the immense number of stars, it is at least reasonable to ask: Are we alone?The answer to this question is extremely important to each of us; for if the answer proves to be "No, we are not alone; and, in fact, there are numerous civilizations throughout the universe," it would force us to re-examine our most deeply held beliefs.
Why? Because, if there are others "out there" many are likely to be thousands or millions of years ahead of us. If ever we were to encounter such overwhelming intellectual and spiritual power, it would be impossible for us to maintain beliefs that were incompatible with theirs. Our belief systems would collapse.
Life as we know it
The basic building blocks of life, as we know it, are built from organic molecules. We know that such molecules are spread throughout the universe. An immediate question is: how easy is it to go from these simple organic molecules to the building blocks of life?
This question was answered in a classic experiment performed in 1952 by the American chemists Stanley Miller and Harold Urey. They showed that simple molecules can combine to form the molecular building blocks of carbon-based life-forms under conditions that are believed to have existed on the Earth in its early history. These building blocks are the amino acids.Of course, this success is only the first step towards life-forms. Somehow we have to get from amino acids to self-replicating molecules. This is where natural selection proves crucial: although the chance of producing the right combination of amino acids to create a viable replicating molecule is essentially zero, it is possible, through natural selection, to get to such a molecule by the cumulative effect of small random changes in a large pool of randomly created molecules. Over time, the population of the more stable, better adapted, molecules would grow at the expense of less stable, less well-adapted, molecules.
SETI: Search for Extra-Terrestrial Intelligence
Assuming that we are not alone, how can we go about finding ET? We believe that the best way to find ET is to listen to possible radio emissions that ETs might be broadcasting. But where to look?
It might make sense to look in a region of the radio spectrum where the radio noise level from the universe is the lowest. The universe emits the least amount of radio energy at the "water hole"--the radio frequency range from 1 to 10 GHz (Giga-Hertz), which is close to the microwave emission lines of H and OH, hence the "water hole".
Or perhaps, aliens would use the the 21-cm emission line of hydrogen because of its universal importance. They might reason that any civilization advanced enough to have invented radio astronomy would surely have discovered this particular radio emission of hydrogen since hydrogen is the most common element in the universe.
In 1960 Frank Drake started "listening" to two Sun-like stars, tau Ceti and epsilon Eridani, using a radio telescope at the National Radio Astronomy Observatory in West Virginia. Unfortunately, he did not discover any signals indicative of ETs. Since Drake's pioneering work, many people have been scanning the universe for signs of intelligent signals, alas, so far without success.Extra-Solar Planets
Perhaps searching for ETs is futile. Life as we know it requires a planet on which to evolve. Even if there are many stars in the universe it may be that planets are extremely rare. The recent discovery of extra-solar planets is therefore extremely exciting because it tells us that planetary systems are common. There could well be more planets in the universe than stars.
The existence of such a huge number of planets significantly enhances the probability that we are not alone, because if solar systems are commonplace then it is much more probable that a planet like the Earth exists elsewhere. However, we should expect the species on these other worlds to be different from those on Earth. But how different?
This is a very difficult question to answer because there is much about life on Earth that we do not understand. Some features may be very peculiar to Earth whilst others, such as eyes, may be universal. On Earth eyes have evolved independently many times suggesting that they confer such fantastic advantage to an organism that eyes are likely evolve elsewhere also. Still, we should not be surprised if ETs turned out to look not a bit like us.
But if, one momentous day, we receive a signal from an extra-terrestrial intelligence we would face the most important, most far-reaching question ever posed:
Should we answer?