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

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 phylogen y Neither a sunburst pattern nor a comparable degree of symmetry is seen in a natural process such as in feline immunodeficiency virus evolution. We t herefore have undertaken forward-process simulation studies employing coale scent theory to investigate whether such highly synchronized subtypes could be readily produced by natural Darwinian evolution. The forward model incl udes both classical (macro) and molecular (micro) epidemiological component s. HIV-1 group M subtype synchrony is quantified using the standard deviati on of the between-subtype distances and the average of the within-subtype d istances. Highly synchronized subtypes and a sunburst phylogeny are not obs erved in our simulated data, leading to the conclusion that a quasi-Lamarck ian, punctuated event occurred. The natural transfer theory for the origin of human acquired immune deficiency syndrome (AIDS) cannot easily be reconc iled with these findings and it is as if a recent non-Darwinian process too k place coincident with the rise of AIDS in Africa.