Scientific Methods

Wednesday, March 29, 2006

Power point Abstract, David Vaughan.

Co-evolution of lice (Phthiraptera) and humans: Did antagonistic host-parasite interactions lead to co-evolution of, and lack of, host-immune responses? (ppt)

David Vaughan

2651582, University of the Western Cape, Bellville, South Africa
(Two Oceans Aquarium, Victoria & Alfred Waterfront, Cape Town, South Africa)


Homo sapiens is parasitized by the head louse ( Pediculus humanus capitus De Geer), the body louse ( Pediculus humanus humanus Linnaeus) and the crab or pubic louse ( Pthirus pubis Linnaeus). P. humanus humanus is the known vector for several rickettsial diseases such as louse-borne typhus, a bacterial disease responsible for more associated mortalities than all the wars combined in history (Abdu F. Azad & Charles B. Beard, 1998). Trench fever caused by the bacterium Bartonella quintana, is transmitted by lice, using humans as reservoirs, causing chronic bacteremia, which is not always easily detectable (Michel Drancourt et al . 2005).

Through evolutionary processes and natural selection, parasitism by lice ( Phthiraptera) fueled adaptation through mutation, defining H. sapiens as visually distinct from the apes, resulting in hairlessness (Markus J. Rantala, 1999).

One of the most interesting facts with the accepted theory of contemporaneous hominids of history, is the (gradual) extinction of the latter in favor of the survival and success of H. sapiens . Indeed evidence supports the co-speciation of H. sapiens with other hominid species of their time, but does not indicate, rather suggests avenues of elimination such as the greater adaptability of H. sapiens to changing environments over their contemporaries, out-competition of resources and even elimination through violent encounters. This presentation will include an additional, untested hypothesis, supported by recent evidence suggesting that direct physical contact occurred between archaic and modern forms of Homo (David L. Reed et al . 2004), that the associated host switching by the lice of the time could have been the mode of transmission of rickettsial diseases, to which H. sapiens serviced a more successful immuno-response over that of their more primitive contemporaries.

The theory is posed as a question, which in itself, if supported by evidence, could possibly strengthen either of the models of human origins, the Recent African Replacement model of Stringer and Andrews, 1988 (David L. Reed et al. 2004), and the Multiregional Evolution model of Wolpoff et al. 1994 (David L. Reed et al. 2004).

In addition, SEMs (scanning electron micrographs) by Prof. Edward Green from MEDUNSA (Medical University of Southern Africa), used with permission, will provide a visual representation of the lice in question, emphasising their remarkable adaptations to a parasitic life-style.


1)Abdu F, Azad and Charles B. Beard (1998) Richettsial Pathogens and their Arthropod Vectors. Emerging Infectious Diseases 4(2): 179-186.
2)David L. Reed, Vincent S. Smith, Shaless L. Hammond, Alan R. Rogers, Dale H Clayton (2004) Genetic Analysis of Lice Supports Direct Contact between Modern and Archaic Humans. Plos Biology 2(11): 1972-1983.
3)Markus J. Rantala (1999) Human nakedness: adaptation against ectoparasites? International Journal of Parasitology 29: 1987-1989.
4)Michel Drancourt, Lam Tran-Hung, Jean Courtin, Henry de Lumley and Didier Raoult (2005) Bartonella quintana in a 4000-Year-Old Human Tooth. Journal of Infectious Diseases 191: 607-611.

David Vaughan
Senior aquarist, Quarantine
Two Oceans Aquarium
Cape Town, South Africa
(021) 418 38 23