PREDICTIONS – 10 Years Later - Santa Fe Institute

5. GOOD GUYS AND BAD GUYS COMPETE THE SAME WAY
available trace the same pattern with exceptional regularity, see Appendix
C, Figure 5.2. Any “comeback” of tuberculosis you may recently
hear about in the news would concern increases in the death rate of
tenths of a percent, imperceptible in the scale of the figure.
Instead of the pronounced deviation at the time of World War I seen in
the case of diphtheria, the tuberculosis data showed a broad peak around
1946, with an increase from 1936 to 1946, the decade leading up to and
including World War II. Such a deviation might be explained by the
poverty and hardships of the Depression, conditions that could result in
a comeback for tuberculosis.
I have seen occasional deviations on the shares of other diseases
phasing out along declining S-shaped trajectories: typhoid, whooping
cough, scarlet fever, gastroenteritis, and pneumonia. Local deviations
can sometimes be due to improper classification. For example, data on
propeller and jet airplanes, both of which have competed with ships in
transatlantic passenger transport, when lumped together do not produce
a smooth growth curve for airplanes. Similarly, the lumping together of
the Spanish flu—which may not have been a flu at all—with pneumonia
produces a noticeable upward deviation at the end of World War I. 6
With time, however, such deviations from the overall trend are eventually
reabsorbed without leaving a long-term trace. The image that
emerges rather reliably from the cases studied so far is that a phasing
out disease empties its niche—its share of all deaths—along an S-
shaped trajectory. The essential message can be summed up as follows:
• Winning the battle against a disease is a process that
proceeds “naturally.” From historical data on the first
half of the process one can forecast the second half.
• A disease starts phasing out well before effective medication
becomes perfected and widespread.
If these hypotheses are true, discovering a vaccine or other effective
cure for AIDS would have been unrealistic before the numbers showed
a relative decline in AIDS victims. When I first analyzed the spread of
AIDS in 1989, I concluded that we should not expect a vaccine for
many years to come. But the number of AIDS victims in the United
States indeed began declining in 1995, and medication improved sig-
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