By Stephen Caesar
Associates for Biblical Research
“Is Malaria Evolving?”
The cover of the March-April 2010 issue of Harvard Magazine features the headline “Malaria: An Elusive, Evolving Foe.” The article inside opens by referring to “a reality of evolutionary biology: EVERYTHING changes and adapts, and microbes have a way of outmaneuvering medicine” (Humphries 2010: 42 [emphasis added]). The clearest case of this phenomenon is malaria, which rapidly adapts to outpace any new drug employed to combat it.
According to the article, “Treating the disease with a drug immediately prompts its evolution toward developing resistance” (Ibid.). For example, after World War II the main anti-malarial drug, quinine, was replaced by a synthetic drug, chloroquine. “Chloroquine resistance emerged separately in Southeast Asia and South America more than 50 years ago, and scientists can trace its origins to mutations in a specific gene. Gradually, the resistant types [of malaria-causing parasite] came to dominate” (Ibid. 42-43).
One notable aspect of this change in the malaria parasite is the extreme rapidity with which it occurs. The article refers to “malaria’s rapid evolution” (Ibid. 43) and further states:
“In Africa, P. falciparum [one of the four parasites that cause malaria] has textbook conditions for an evolutionary perfect storm. With its two hosts [humans and mosquitoes] living in close proximity, the parasite has many opportunities to mate and diversify, but the bottlenecks it faces as it moves between mosquito and human ensure that only the best adapted individuals survive. This abundant variation, when combined with stringent selection, fosters rapid evolution” (Ibid. 45).
The article then points out that the human species has likewise adapted to meet the onslaught of the malaria parasite:
“…[T]he parasite’s numbers exploded around the time agriculture was developed 10,000 years ago. Humans were then living in denser populations and clearing land for fields and settlements, which meant that some of them were living close to wet habitats where mosquitoes bred. Much of the malaria genome evolved after this large expansion, which was also when the mosquito species that transmit malaria began to expand and diversify” (Ibid. 45-46).
The article immediately goes on to state:
“Scientists looking at the human genome can see that malaria has been one of the most important factors in shaping it ever since. The disease has a direct effect on human survival and reproduction….In fact, it was human adaptation to malaria that provided the first direct evidence that the human race has indeed evolved….[S]ickle cell anemia was found to arise from a genetic adaptation that protects people from malaria. Other blood disorders have subsequently been linked to malaria resistance as well, which helps explain why these seemingly harmful genetic diseases have become prevalent among people living in tropical areas” (Ibid. 46).
There are three important points to keep in mind. First, when the article mentions “evolution,” it is referring to changes within a species. For example, it explicitly compares human evolution to the evolution of the four micro-organisms that cause malaria, yet, just as humans are still humans 10,000 years after suffering their first assault from malaria-causing parasites, the four parasites are still the same species. Second, as already mentioned, these micro-evolutionary changes have occurred rapidly, sometimes even within a few years of a new drug having been introduced to combat malaria. Third, as has been discussed several times in previous installments of this column, when a species (including humanity), micro-evolves to adapt to a new threat, it does so at a “fitness cost,” that is, it grows stronger in its ability to combat the new threat (e.g., malaria), but gets weaker in another area (e.g., blood disorders in people who have built up an immunity to malaria).
In light of this, the use of the term “evolution” in the Harvard Magazine article is not to be taken in the strict Darwinian sense of one species eventually turning into a new, different, superior species over millions of years. In both humans and the malarial parasites, they’re still the same species.
Humphries, C. 2010. “An Evolving Foe: Applying Genomic Tools to the Fight against Malaria.” Harvard Magazine 112, no. 4.
Stephen Caesar holds his master’s degree in anthropology/archaeology from Harvard. He is a staff member at Associates for Biblical Research.