Family tree for Pennys eleven species

If molecular genetic technology continues to expand at its present exponential rate, by the year 2050 deriving the complete sequence of an animal's genome will be cheap and quick, scarcely any more trouble than taking its temperature or its blood pressure. Why do I say that genetic technology is expanding exponentially? Could we even measure it? There is a parallel in computer technology called Moore's Law. Named after Gordon Moore, one of the founders of the Intel computer chip company, it can be expressed in various ways because several measures of computer power are linked to each other. One version of the law states that the number of units that can be packed into an integrated circuit of a given size doubles every eighteen months to two years or so. It is an empirical law, meaning that, rather than deriving from some piece of theory, it just turns out to be true when you measure the data. It has held good over a period of about fifty years so far, and many experts think it will do so for at least a few more decades. Other exponential trends, with a similar doubling time, which can be regarded as versions of Moore's Law, include the increase in speed of computation, and size of memory, per unit cost. Exponential trends always lead to startling results, as Darwin demonstrated when, with the aid of his mathematician son George, he took the elephant as an example of a slow-breeding animal and showed that, in just a few centuries of unrestricted exponential growth, the descendants of just one pair of elephants would carpet the earth. Needless to say, population growth of elephants is not, in practice, exponential. It is limited by competition for food and space, by disease, and by many other things. That, indeed, was Darwin's whole point, for that is where natural selection steps in.

But Moore's Law really has remained in force, at least approximately, for fifty years. Although nobody has a very clear idea why, various measures of computer power actually have increased exponentially in practice, where Darwin's elephant trend is exponential only in theory. It occurred to me that there might be a similar law in force for genetic technology and the sequencing of DNA. I suggested it to Jonathan Hodgkin, Oxford's Professor of Genetics (who had once been an undergraduate pupil of mine). To my delight, it turned out that he had already thought of it - and measured it, in preparation for a lecture at his old school. He estimated the cost of sequencing a standard length of DNA at four dates in history, 1965, 1975, 1995 and 2000. I inverted his figures to 'bangs for the buck', or 'How much DNA could you sequence for £1,000?' I plotted the figures on a logarithmic scale, chosen because an exponential trend will always show up as a straight line when plotted logarithmically. Sure enough, Hodgkin's four points fall pretty well on a straight line. I fitted a line to the points (for the technique of linear regression, see note on p. 112) and then took the liberty of projecting it on into the future. More recently, just as this book was going to press, I showed this section to Professor Hodgkin, and he told me the most recent data of which he was aware: the duckbilled platypus genome, which was sequenced in 2008 (the platypus was a good choice, because of its strategic position in the tree of life: the ancestor that it shares with us lived 180 million years ago, which is nearly three times as long ago as the extinction of the dinosaurs). I've drawn the platypus's point as a star on the graph, and you can see that it fits pretty well near the projected line that was calculated from the earlier data.

The slope of the line for what I am now calling (without permission) Hodgkin's Law is only slightly shallower than that for Moore's Law. The doubling time is a bit more than two years, where the Moore's Law doubling time is a bit less than two years. DNA technology is intensely dependent on computers, so it's a good guess that Hodgkin's Law is at least partly dependent on Moore's Law. The arrows on the right indicate the genome sizes of various creatures. If you follow the arrow towards the left until it hits the sloping line of Hodgkin's Law, you can read off an estimate of when it will be possible to sequence a genome the same size as the creature concerned for only £1,000 (of today's money). For a genome the size of yeast's, we need wait only till about 2020. For a new mammal genome (as far as this kind of back-of-envelope calculation is concerned, all mammals are equally expensive), the estimated date is just this side of 2040. It's an exhilarating prospect: a massive database of DNA sequences, cheaply and easily obtained from all corners of the animal and plant kingdoms. Detailed DNA comparisons will fill in all the gaps in our knowledge about the actual evolutionary relatedness of every species to every other: we shall know, with complete certainty, the entire family tree of all living creatures.* Goodness knows how we'll plot it; it won't fit on any practical-sized sheet of paper.

Llpiii regreB&lon 1iMeif to lour ij.i1 j pon Ms. Hi ¿ii eitrapol-atfd La ZO&D

Llpiii regreB&lon 1iMeif to lour ij.i1 j pon Ms. Hi ¿ii eitrapol-atfd La ZO&D

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