LITMIR.BIZ

      The type specimen of the duck-billed platypus (Ornithorhynchus anatinus). This animal was not believed to be real when it was first described.

      Duck-billed platypus. Photo © Natural History Museum, London.

      The taxonomic process as I have described it would certainly have applied at the time I first nosed my way cautiously around the maze of offices and corridors in the Natural History Museum. I still believe today in the primacy of collections and specimens – they don’t go out of fashion, because they are preserved to outlive any passing phase of epistemology. However, it would be surprising if there had not been changes in scientific practice and theory over the last decades, if only because science always moves on. I deliberately concentrated on species above, because that basic unit has retained its central role in systematics, no matter how technique and theory have changed elsewhere. Species are not merely specious.

      The most important change in the scientific firmament was the appearance of molecular techniques. The possibility of sequencing genes followed upon the unravelling of the structure of DNA – and now has reached new heights after the decoding of entire genomes, including that of our own species. What began as a major technical challenge is now almost entirely routine, and every research institute worth its salt, including the Natural History Museum, has a molecular biology laboratory, staffed by scientists of the white-coated variety, slaving away with test tubes in front of highly sterile machines. Nowadays, an organism must reveal its secrets down to the molecules in its DNA or RNA. Gene sequences provide a whole plethora of characters to add to the traditional morphology – something to challenge the hairs on legs, spines on shells, pattern of bones or structure of flowers. Because the genome is almost unimaginably huge, the potential for information locked in its sequences of bases is theoretically almost endless. It is small wonder that there has been a boom in the employment of molecular biologists at the expense of traditional experts on groups of organisms.

      More than twenty years on from the appearance of these techniques it is possible to see just how many questions can now be tackled which were previously beyond reach. Many people have used the obvious pun ‘designer genes’ before, but it is not a bad phrase to summarize what scientists actually do with the vastness of the genome. They use different parts of it for different purposes. If they have been curated appropriately, pieces of type specimens can even be fed into the DNA factory, thanks to a technique known as PCR that ‘magnifies’ sequence information from tiny pieces of tissue. There is, of course, much variation in the genome within a species. Some variation is at the level of the individual – hence the possibility of ‘nailing’ a criminal for an offence using stored samples such as blood or semen years after a deed has been committed. The gene sequences in question identify a particular person beyond doubt, like a fingerprint. Other changes in gene sequences are conserved for slightly longer periods of time; sections of DNA called microsatellites have high rates of mutation, which makes them ideal for studies within the historical time span and within species – for example, in tracing movements of human populations around the world. Other parts of the genome change still more slowly, and yield sequences that are of particular use in recognizing species – we will come back to these again, because they are of special importance in taxonomy. Other parts of the genome are generally conserved, which means they accumulate changes only very slowly, over millions of years, or even longer. Some of these genes are important in the functioning of any organism – they include genes that encode proteins, for example. Or there is the RNA of the cell’s ‘powerhouse’ organelle, the mitochondrion, which was one of the first molecules of this kind to be completely sequenced. Such slowly changing genes and sequences allow the scientist to ‘see’ backwards in time to the divergence of major lines of evolution, to examine relationships between different groups of organisms that might previously only have been investigated by the palaeontologist delving deep in the fossil record. To say that these discoveries had a profound effect on systematics would be a considerable understatement: it provided a whole new way of looking at the natural world. There are even genes that could potentially ‘see’ the separation of the major designs of animals and plants hundreds – even thousands – of millions of years ago. In 1991 great surprise greeted the discovery that the sequence of the elongation factor gene in the nematode worm Coenorhabditis elegans was more than 80 per cent similar to that in a mammal; here was common ancestry writ large. Some genes were evidently so deep-seated that they continued to do their work over a timescale of many, many millions of years. Such evidence proved beyond question that we are one with the worm and the bacterium.