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Outbreeding Depression Definition

By Contributor ; Updated September 21, 2017

Outbreeding depression is a scientific term that refers to when two distant relatives of the same species produce offspring less fit than themselves. These hybrids are generally eradicated through natural selection due to their inferior survival capacity. Scientists, however, use the study of outbreeding depressions to ensure the survival of some and avert the disasters of others.

Predicting the survivability of offspring engineered through crossbreeding is essential to ecologists, pathologists and botanists. Outbreeding depressions can indicate which newly developed crop should be planted, where a species should or should not be relocated, or what diseases may be propagated by the breeding of unsuitable mates.


Outbreeding occurs when two dissimilar individuals belonging to the same species reproduce. The terms 'outbreeding' and 'crossbreeding' are sometimes used interchangeably. Hybrid dogs like the Cockapoo, an outbreeding of Cocker Spaniel and Poodle breeds, are living examples of the process. Outbreeding can occur in plants, animals, microscopic organisms, and even humans. Outbreeding can be either naturally occurring or the result of scientific intervention and may have positive or negative results.

Outbreeding Depression

Outbreeding can be either beneficial or detrimental to the resulting offspring. Crossbreeding which results in disadvantage to offspring is considered an outbreeding depression. Distinct genetic traits of either parent combine to produce new traits, which hinder the survival of the resulting offspring.

Michael Lynch of the University of Oregon's Department of Biology offers the example of fish. Hatchery fish and wild fish possess specific traits, particularly size, that are beneficial for their unique environments. Outbreeding between these two dissimilar gene pools of the same species can result in offspring of size that is neither complementary to survival in the hatchery or in the wild. The combination of genes from the dissimilar progeny (parents) can result in genetic traits that render the offspring less fit than either parent.


Studying the results of outbreeding, whether by natural occurrence or human intervention, offers animal scientists a powerful tool in combating the extinction of species.Springer Link posts the abstract of a collaborative study in which scientists examined the effects of outbreeding depression in diminishing frog populations.

The study revealed crossing dissimilar adults of the same species resulted in smaller offspring with lower survival rates. Researchers concluded that the species would likely be harmed by mating between dissimilar frogs and warned caution should be used to prevent outbreeding depression. Such a depression would likely hasten the reduction of frog numbers, contributing to their extinction.


The University of Wisconsin's School of Veterinary Medicine shares the results of research in which an outbreeding depression was exposed in largemouth bass. Fish were taken from separate regions of Illinois and Wisconsin for use in the study. Both varieties of largemouth bass displayed genetic adaptations to their unique environments, making them suitable for outbreeding.

The resulting offspring were found to be less fit than the adults from either progeny sample. The hybrid bass were less resistant to viral infection. Researchers concluded that further breeding between the two groups would result in genetic traits that were detrimental to the offspring and the species as a whole. The research serves as a warning about the potential dangers of animal translocation by humans.


The need for stronger, more plentiful crops drives massive research campaigns in agriculture. Botanists conduct crossbreeding experiments to develop hybrid improvements of existing plant life. The resulting plants can show great potential, but they may also display signs of outbreeding depression. Studies conducted by the American Journal of Botany on a number of these experiments show great attention is paid to the potential for disaster in hybrids. Identifying outbreeding depressions in small scale research can help avoid financial disaster for the farming industry and food shortages worldwide.


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