Further Evidence of the Cost of Microevolution

by Stephen Caesar

Previously (see January issue of Pulpit Helps), I discussed how experiments on fruit flies demonstrated that when a species develops improvements within its pre-set genetic boundaries (microevolution), it not only fails to become a newer, higher species (macroevolution), but it also pays a price for its improvement by becoming disadvantaged elsewhere. In a process called "artificial selection," flies were intentionally bred to develop increased resistance to parasitic wasps. The hope was that, in accordance with macroevolutionary theory, the flies would keep improving their wasp resistance to the point where they would evolve into a new species that was 100% wasp-resistant. Continuous breeding, however, failed to produce flies that had anything higher than a 60% resistance to the wasps, and the flies were weaker, shorter-lived, and less able to compete for food than individuals that did not undergo the improvement (Zimmer 49-50).

Such disadvantages are called "fitness costs" (Read & Allen 1104). This term refers to the fact that creatures undergoing minor improvements to increase their chances of survival (like building up immunity to parasites) do not macro-evolve into higher species, but actually have to sacrifice part of their vitality to make up for the improvements. In other words, animals only have a limited "budget" for improvement. If they "increase spending" on fighting parasites, they must "decrease spending" on strength, size, lifespan, etc.

Experimentation has demonstrated that what is true for fruit flies holds true for other animals and for humans. Science magazine reported: "In taxa [major animal groups] as diverse as snails, moths, mosquitoes, and fruit flies, artificial selection in the laboratory for increased ability to resist parasite attack has been associated with reductions in at least some components of fitness." The intentional breeding of bumblebees to fend off internal parasites "dramatically reduced their survival compared to bees that were not immunologically challenged." An attempt to increase wild birds' immunity to tetanus and diphtheria gave the following result: "Immunized birds fledged [became the parents of] fewer and lighter offspring than non-immunized birds" (ibid.).

These "fitness costs" also occur when humans build up resistance to parasites. In Africa, where malaria is prevalent, local populations have, over time and through random genetic mutations, developed an increased resistance to Plasmodium vivax, the mosquito-borne parasite that causes malaria. This increased resistance, so necessary to survive in Africa, comes with a price: the Harvard University Gazette reported that the mutation that increases resistance to malaria "causes sickle cell anemia, a painful inherited blood disease that occurs mainly in blacks. Sickle cell anemia, however, is not usually fatal" (Cromie 4). Thus, the improvement Africans undergo to fight a lethal disease (malaria) is offset by a painful, debilitating, but not fatal, disease (sickle cell anemia). This is a perfect example of how minor improvements within the boundaries of a single species demand a "fitness cost," rather than serving as a rung on an alleged ladder that leads to a new, higher species.

The conclusion is this: intraspecific microevolution (small genetic mutations that occur within a species in order to protect that species from biological attacks) is scientifically proven. However, transpecific macroevolution (the transformation of this micro-mutating species into a completely new creature) is devoid of scientific proof. Micro-mutating species do not keep mutating until they transform into higher life forms; instead, they sacrifice part of themselves, ultimately resulting in the same species all along.


Cromie, William J. (2001). "Evolution at work: The tale of a tail." Harvard University Gazette, 8 February.

Read, A. F., and J. E. Allen. (2000). "The Economics of Immunity." Science 290, no. 5495.

Zimmer, Carl. (2000). "Attack and Counterattack: The Never-Ending Story of Hosts and Parasites." Natural History 109, no. 7.

Stephen Caesar is currently pursuing his master's degree in anthropology/archaeology at Harvard University. He is the author of the e-book The Bible Encounters Modern Science, available at www.1stbooks.com.

2011 Disciple 155x50 2011 AMG 155x50
Disciple Banner Ad