Darwinian molecular imaging

Abstract

On 12 February 2009, we celebrated the 200th anniversaryof Charles Darwin’s birthday. His theory of evolutionthrough natural selection [1] is a most famous biologicalconcept, with a notoriety as wide as Albert Einstein’sconcept of relativity in physics. If, as Dobzhanskyprovocatively stated, “Nothing in biology makes senseexcept in the light of evolution” [2], then it is worthwhilethat we, as molecular imaging practitioners and scientists,should ask ourselves how much Darwinian is molecularimaging today. What use of Darwin’s theory of evolutionthrough natural selection is made in the fields of molecularimaging and nuclear medicine? Is the evolution theoryconceptually useful or a mere theoretical notion occasion-ally discussed by basic researchers in molecular imaging?Could the introduction of Darwinian concepts be operant toevolve more efficient and better molecular imaging? Now200 years after his birth and 150 years after the first editionof his famous book, one of the greatest successes inscientific publishing ever (the first edition sold out in just1 day), it appears timely for molecular imaging to takestock of Darwin’s heritage.Darwin’s theory of evolution through natural selectionIn 1859, Charles Darwin published On the Origin ofSpecies by Means of Natural Selection, or the Preservationof Favoured Races in the Struggle for Life [3]. The theoryof natural selection results from insightful connectionsbetween a huge corpus of meticulous observations of livingspecies, both animals and plants, wild and domesticated,collected during 30 years of scientific activity.Several exegetes (see among others Ernst Mayr, Dobz-hansky, Patrick Tort) have unveiled the logics of construc-tion of Darwin’s theory, which we briefly summarize herein four principles:1. Principle of variability: both wild and domestic animalsexhibit phenotypic variation; hence, living species havea natural propensity towards variation.2. Principle of the limitation of population size: thereproduction capacity of most species is so high that,in the absence of limitation, they would grow expo-nentially. This is not observed and population sizesgenerally tend to be stable because a regulatory factorlimits population sizes.3. Principle of selection: breeders and farmers selectvariations that they deem advantageous by allowing onlythoseindividualswithdesiredtraitstoproduceanoffspring.Several of these traits are transmitted to the offspring.4. Principle of the survival of the fittest: similar to thelimitation of population sizes by breeders, competitionfor survival is observed throughout natural populations.Only individuals that have inherited the genetic traitsbest adapted to their environment survive and produceoffspring. Therefore, in a given environment thedriving force for selection is the struggle for life andonly the best fit to that environment survive.