SEARCHING FOR THE ORIGIN OF LIFE
DNA AND INFORMATION
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Question from Chapter 5
Where did the information in the first life molecules come from? Could DNA acquire information by natural processes?
To date, no-one has suggested DNA could have been the first molecule to occur spontaneously as a result of the Natural Properties of the earth and sun because DNA is much more complex than RNA. DNA consists of two strands neatly aligned with one another, then coiled into a helix. DNA carries the information for each living creature to make all the biological molecules it needs. This information is called the genetic code.
Each cell in a living organism contains all the genetic code for the organism, and when cells divide the DNA in the cell is copied so that each new cell gets a complete copy. Therefore, all the living cells on earth today have inherited their genetic information from the DNA in the cells they were derived from, which means all present day DNA molecules have got their information from other DNA molecules.
How does DNA copy its information?
DNA does not copy itself. It can only be copied if a number of proteins and other molecules work on it. One group of proteins with a special role in this process is called DNA polymerase. Like proteins in all living cells, DNA Polymerase is made from exclusively left handed amino acids, which brings us full circle in our search for the origin of living molecules. It also brings us to our other serious problem for the origin of life. DNA polymerase can only carry out its function because it has the right structure, i.e. the right sequence of amino acids.
The structure of DNA polymerase is determined by information stored on DNA, but it takes DNA polymerase and other proteins to make DNA. Furthermore, information to make DNA polymerase must be transferred to RNA before it can be used to make proteins from amino acids. Making the RNA copy also requires proteins.
This problem can be expressed using the diagram below.
Can you see where the process has a beginning? Could any of it function before the whole system was complete?
This system will not work unless all the components are present and functioning. This means that in order to start life you must have proteins and RNA and DNA.
Another DNA Polymerase Problem.
One function of DNA Polymerase is to ensure the information on DNA is copied correctly. As each new nucleotide is added to a newly forming DNA copy, DNA polymerase checks that it is the correct one, and if a mistake has been made, replaces it with a correct one.
This raises an interesting problem for the theory of evolution.
Evolutionary theory states that after the first life form arose from non living matter it gave rise to many new and different life forms. We can express this sequence of events with our formula as follows:
Matter + Energy + Time ® Life Form 1
Then: Life Form 1 + E + T ® Life Forms 1 + 2 + 3 ... etc.
Or, in shorthand
L1 + E + T ® L1 + L2 + L3
Each new life form would have new and different DNA. Therefore we can express the changes involved in making new living things by naturalistic evolution as:
DNA1 + E + T ® DNA1 + DNA2 + DNA3 ... etc.
Are there any observations of such evolutionary progression happening?
A Classic Study
An example that is often used as an example of evolution is "Darwin's Finches". These are a group of small birds that live on the Galapagos Islands in the Pacific Ocean, off the coast of South America.
During his visit to the Galapagos Island Charles Darwin collected specimens of the finches and classified them into the nine species. Since then other scientists have studied the birds and classified them as 12 or 13 species, on the basis of overall size, beak shape, feeding habits and colour. Darwin suggested (and no-one disputes it) that the birds were the descendents of an ancestral group of finches that somehow migrated to the islands from South America. As they spread out among the different islands they split up into the different distinctive varieties under the influences of environmental pressures, such as what type of food was most available. The most distinctive variation among the different species is their beak shape and feeding habits.
In spite the great variety of beaks, the birds are otherwise fairly similar and if they are allowed to cross-breed, the resulting offspring that can sing, court, mate and produce fertile offspring. This indicates that they are not really different species, and the reason they don't normally interbreed is lack of opportunity because they live in different habitats, rather than biological inability.
So, what caused the different beak shapes? Is this evolution of new species?
Recent studies of the finches provides clue as to what has happened to them since they first moved to the islands. In 2002 the results of a thirty year study of two species of finches on the island of Daphne Major was published. Average beak size in both species changed after drought or rain caused different kinds of seeds to be more are less abundant. If there were fewer small seeds, birds with the smallest beaks died out and larger beaked birds survived and reproduced, so the next generation had larger beaks, vice versa. If the two species interbred they had offspring with intermediate size beaks, and provided there was suitable food available, these intermediate birds survived and bred. Meanwhile, other researchers have identified two chemicals, CaM and Bmp4, that control the size and shape of the beak as the embryo birds are developing in the egg. They worked out that variations in these two chemicals could account for the whole range of different beak shapes in all the Galapagos finches.
(References: Science, vol. 296, p707, 26 Apr 2002; Nature, vol 442, p563, 3 Aug 2006)
Putting this evidence together, we should ask: Has evolution of new life forms occurred amongst Darwin's finches?
The answer is definitely not!
All that has happened is on each island the birds whose beaks were most suited to the most abundant food source survived and reproduced at the expense of those less suited to that island's food. This process is called Natural Selection, or "survival of the fittest".
However, survival of the fittest does not explain the arrival of the fittest, i.e. how living things came to have the characteristics that enable them to survive. The fact that finches, which already had beaks before they arrived on the islands, gave rise to finches with varying sizes and shapes of beaks after they lived on the islands for a few generations, does not explain how birds came to have beaks, or how birds came into existence.
For evolution to be true the following events must have happened before the ancestral finches moved to the Galapagos Islands:
Simple Molecules → Complex Molecules → Cells → Multi-Cellular Animals → Reptiles (no beaks) → Birds (with beaks)
Now consider that same sequence in terms of DNA information:
No DNA, therefore no code or information → DNA, some coded information → DNA, animal without beak → DNA, bird, with beak
For evolution to have occurred DNA information must have increased from zero information, to millions of bits of information, all by natural processes.
Could DNA code have generated itself from non biological molecules, and then progressively added more coded information by exclusively naturalistic processes?
To see whether this could have happened we need to check out the properties of codes. We will do this in the next Chapter 7.
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