Fitness is a measure of reproductive success. It is used to assess the advantages and disadvantages of an adaptation.[1] This adaptation can be opposable thumbs or the loss of eyes. The idea of fitness is used in a medical sense to determine which individuals are most susceptible to a disease or disease process.

Inclusive Fitness (increase in probability of reproductive success) is gained through helping family members. This causes alleles with the highest fitness to increase in frequency within the population[2] .Any advantage and individual can gain over another individual adds to their fitness; while any negative adaptation detracts from their fitness.


The first evolutionary hypothesis was created by Jean Baptiste Lamarck. He hypothesized that although all creatures were created perfect, they have a need to change as their environment changes. He wrote that characteristics which are acquired throughout an individual's life time are passed on to their offspring. If the characteristics are beneficial they will be passed on to more offspring than if they are not beneficial. These changes are perpetuated through the survival of individuals which are more suited for the environment in which they reside; individuals which have a greater degree of fitness. He is best known for using the necks of giraffes as an example. He concluded that the necks of giraffes are long due to the stretching of their necks while reaching for the leaves at the tops of trees. By reaching the leaves at the very top of the trees the individual has less competition from other giraffes. The giraffe can have a shorter neck but it will lengthen after a long period of stretching. The offspring of the giraffes that stretch out their necks will be born with longer necks than their parents were born with and will therefore have to stretch their necks less.

Jean Baptist Lamarck

Lamarck's hypothesis has since been disproven but it was a very important step in evolutionary theory. At the time Lamarck posed his theory the prevailing thoughts on evolution were based in religion. It was believed that all of God's creatures were created in perfection an therefore had not changed throughout history because they had no need to change. Lamarck's theory in evolution was a mix of the scientific feelings at the time and the views of the church and the public. Lamarck paved the way fot the acceptance of more substantiated evolutionary theories such as those of Charles Darwin and Alfred Russel Wallace. Darwin's best known work is The Origin of Species. It was actually meant as an abstract to a much longer paper but Darwin never got the chance to finish it.

Even though Darwin is now regarded as a revolutionary individual by the scientific community, and his theories that would be included in the Origin were mostly refined and completed in 1840, the Origin was not published until 1859. This could be because Darwin was worried about the backlash that the manuscript would cause. Darwin was not very well known and
Charles Darwin
most of his research was centered on barnacles. He actually wrote a paper on Natural Selection which he intended to have published upon his death. This would have meant that he would not witness the criticism that would come with a direct contradiction of the church. He was forced to publish his findings in 1859 when he received a manuscript from a friend, Alfred Russel Wallace. Wallace had come to the same conclusion as Darwin independently and without knowing about The Origin of Species had sent Darwin a copy of the manuscript for revision before its presentation at a meeting of the Linnean Society in London in 1858. Darwin told Wallace about his discoveries and they presented their findings together at the meeting.

After receiving Wallace's paper Darwin became afraid that another scientist might publish a paper about natural selection before he could. He hurriedly compiled his notes into The Origin of Species intending on completing the work for a second publication.[3]

Anthropological Study

Example 1

In areas where there is a high incidence of hypoxia; due to the decreasing oxygen with increasing altitude due to the fall in barometric pressure in higher altitudes; there is a genotype which is linked to a higher oxygen saturation in the blood. From a previous study it has been shown that there are high values for heritability in the hemoglobin concentration and oxygen saturation in the populations of focus in this study.There is significant evidence for a "major gene for oxygen saturation;" individuals which have this allele have a 5-6% higher oxygen saturation than those which do not have the allele. [4]

Some women are estimated to "have a high probability to have high oxygen saturation genotypes" while other women "have a high probability to have the low oxygen genotype." The women which have the "high oxygen saturation genotypes" will pass on that genotype to their offspring (the high oxygen saturationgenotype is the dominant genotype). There is a marked decrease in infant mortality and aborted fetuses among women which have the higher oxygen saturation genotype that the women with the low oxygen saturation genotype. This is evidence for a higher group fitness among the women which have the high oxygen saturation genotype. These women will have more offspring which survive to reproductive age. Eventually the high oxygen saturation genotype will become fixed within the population making it distinct from other populations at that locus[5] .


Example 2

According to Dr. Matt Gilg at the University of North Florida, early reproductive events have a greater effect on fitness than late reproductive events. He provides two of the many reasons for this. One: A higher proportion of population will survive to reproduce at younger ages than at older ages. And two: if mx (mx– average number of offspring born to a female of age x) remains constant the more offspring will be produced in early reproductive events).

For example:

If mx =2 at all ages

-100 females survive at age 2= 100*2= 200 offspring (has a greater effect on r- fitness – intrinsic rate of growth (of genotype or population)
- r = (lxmx)
-60 females survive at age 3= 60*2= 120 offspring

Also if reproductive events occur earlier than there is greater opportunity for the individual to reproduce within its lifetime, adding to its overall fitness. The offspring of earlier reproductive events will reach reproductive age earlier than those individuals from reproductive events which occurred later. Becoming reproductively active earlier the individual has an advantage to produce offspring earlier and therefore will contribute to population growth earlier. The genes of the offspring of earlier reproductions will contribute genetic makeup to more individuals. Offspring from individuals with greater fitness will be more fit as long as the climate and competition for resources stays relatively constant.[6]

Example 3

Figure 1. Biston betularia lightly colored and darkly colored (Natural Selection 2010).

Fitness can be greatly affected by population perturbations. A study by Bernard Kettlewell in 1956 on the Peppered Moth, Biston betularia, showed changes in fitness directly correlated with habitat changes. His work on Biston betularia, covered color changes from following the industrial revolution. Before the industrial revolution the majority of peppered moths were lightly colored (see right). Following the industrial revolution the majority of Peppered Moths were darker in color. There is a spectrum of colors included in the colors of the Peppered Moth; figure 1 shows the two extremes created by selection.

Kettlewell concluded that prior to the industrial revolution moths with lighter coloration had a higher degree of fitness than those of darker color. He theorized this from the light color of the trees within the moths’ habitat. The industrial revolution brought about industrial melanism, the darkening of the trees from the pollution produced by industries. The darker trees caused the darker moths to have better camouflage from predators. Therefore the darker moths now had the greater fitness.[7][8]

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Additional Resources


Case Western Reserve University (2007, November 2). Elevated Nitric Oxide In Blood Is Key To High Altitude Function For Tibetans. ScienceDaily. Retrieved October 11, 2010, from­ /releases/2007/10/071030095520.htm

Darwin, Charles. The Origin of Species by Means of Natural Selection of the Preservation of Favoured Races in the Struggle for Life. 150th Anniversary ed. New York: Signet Classics, 2009. Print.

Werf, Julius Van Der. Adaptation and Fitness in Animal Populations: Evolutionary and Breeding Perspectives on Genetic Resource Management. 1st ed. Springer: Springer, 2009. Print.

"Darwinian fitness." Encyclopædia Britannica. 2010. Encyclopædia Britannica Online. 28 Sep. 2010 <>.

"Natural Selection - VELS Standards and Focus Ideas - Science Continuum P-10 - Department of Education and Early Childhood Development." Department of Education and Early Childhood Development - Department of Education and Early Childhood Development. 13 Nov. 2009. Web. 28 Sept. 2010.

Related Terms

  • Fecundity
  • Heritability (H2)[9]
    • Inclusive Fitness
    • Life-History characteristics (traits)- a suite of co-evolved traits that have a direct effect on fitness; average measures of the different fitness characteristics of a genotype/ population (Gilg, 16 Feb 2010).
    • Natural Selection
    • Reproductive Fitness


  1. ^ Wiley, Andrea S., Allen, and John S. 2009 Medical Anthropology: A Biocultural Approach. New York: Oxford University Press.
  2. ^ Gilg, Matt. Behavioral Ecology. Evolution. University of North Florida, Jacksonville Florida. 22 Mar. 2010. Lecture.
  3. ^ Gilg, Matt. History of Evolutionary Biology." Evolution. University of North Florida, Jacksonville Florida. Jan. 2010. Lecture.
  4. ^ Beall, Cynthia M. (2006) Andean, Tibetan and Ethiopian Patterns of Adaptation to High-altitude Hypoxia. Integrative and Comparative BIOLOGY 46.1: 18-24.
  5. ^ Beall, Cynthia M. (2006) Andean, Tibetan and Ethiopian Patterns of Adaptation to High-altitude Hypoxia. Integrative and Comparative BIOLOGY. 46.1: 18-24.
  6. ^ Gilg, Matt. Life-History Evolution. Evolution. University of North Florida, Jacksonville Florida. 16 Feb. 2010. Lecture.
  7. ^ "Kettlewell's Experiments | NCSE." NCSE | National Center for Science Education - Defending the Teaching of Evolution in Public Schools. 2 Oct. 2008. Web. 22 Sept. 2010.
  8. ^ Gilg, Matt. FDS- Frequency Dependant Selection. Evolution. University of North Florida, Jacksonville Florida. 8 Feb. 2010. Lecture.
  9. ^ Case Western Reserve University (2007, November 2). Elevated Nitric Oxide In Blood Is Key To High Altitude Function For Tibetans. ScienceDaily. Retrieved October 11, 2010, from­/releases/2007/10/071030095520.htm
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