The origin of acquired immune deficiency syndrome: Darwinian or Lamarckian?

Abstract

The subtypes of human immunodeficiency virus type 1 (HIV–1) group M exhibit a remarkable similarity in their between–subtype distances, which we refer to as high synchrony. The shape of the phylogenetic tree of these subtypes is referred to as a sunburst to distinguish it from a simple star phylogeny. Neither a sunburst pattern nor a comparable degree of symmetry is seen in a natural process such as in feline immunodeficiency virus evolution. We therefore have undertaken forward–process simulation studies employing coalescent theory to investigate whether such highly synchronized subtypes could be readily produced by natural Darwinian evolution. The forward model includes both classical (macro) and molecular (micro) epidemiological components. HIV–1 group M subtype synchrony is quantified using the standard deviation of the between–subtype distances and the average of the within–subtype distances. Highly synchronized subtypes and a sunburst phylogeny are not observed in our simulated data, leading to the conclusion that a quasi–Lamarckian, punctuated event occurred. The natural transfer theory for the origin of human acquired immune deficiency syndrome (AIDS) cannot easily be reconciled with these findings and it is as if a recent non–Darwinian process took place coincident with the rise of AIDS in Africa.