Community hub
Recent from talks
Knowledge base stats:
Talk channels stats:
Members stats:
Parasite-stress theory
Parasite-stress theory, or pathogen-stress theory, is a theory of human evolution proposing that parasites and diseases encountered by a species shape the development of species' values and qualities, proposed by researchers Corey Fincher and Randy Thornhill.
The differences in how parasites and diseases stress people's development is what leads to differences in their biological mate value and mate preferences, as well as differences across culture. Parasites causing diseases pose potential ecological hazards and, subsequently, selection pressures can alter psychological and social behaviours of humans, as well as have an influence on their immune systems.
Several hypotheses have attempted to explain how parasite load influences female mate choice, as certain traits are thought to be costly and the expression of such traits may be indicative of genetic quality.
According to the Hamilton–Zuk hypothesis, female mate choice is based on the extent to which male secondary sexual characteristics are expressed, as these are thought to be indicative of a heritable resistance to pathogens. A meta-analysis reviewed studies exploring the magnitude of the relationship between expression of secondary sexual characteristics and parasite intensity, as well as level of host immune functioning. Consistent with the hypothesis proposed by Hamilton and Zuk, the meta-analysis revealed that males with the fewest parasites and/or the strongest immune systems typically had the most extravagant secondary sexual characteristics. With regards to parasite-stress theory, these findings would be interpreted as those men who have encountered more parasites – or are naturally less capable of dealing with parasites – are also less desirable mates to females, due to a lower genetic quality for the potential offspring.
The Zahavi handicap principle, originally proposed by Zahavi in 1975, suggests that males who possess secondary sexual characteristics which provide a handicap are more attractive to females. These sexual ornaments are sexually selected in order to appear stronger and better adapted, compared to other males in the environment. This is because these characteristics are indicators of good genes and heritable viability, as they are costly to an individual's survival to maintain and produce. Therefore, the stronger the individual is, the more able they are to bear this cost.[citation needed]
These kinds of characteristics are a form of communication within species, as they are defined as honest signals (a signal about a mate's quality which cannot be faked). As a weak individual would not be able to survive with this particular characteristic, it signals to potential mates that it is stronger than its competitors and has a high mate value. Examples of such traits include the peacock's tail, very bright in nature and hence attracting more attention from predators as well as requiring more energy to maintain. Another example is the gazelle's stotting behaviour, whereby the gazelle jumps up and down when it spots a predator, in order to indicate its physical fitness.
This hypothesis takes Zahavi's principle further in suggesting that testosterone is responsible for the production of male secondary sexual traits while also suppressing the immune system. It therefore proposes that these traits are honest signals of mate quality because only males with 'good genes' should be able to fully express them without being vulnerable to parasite attack. Males will, therefore, demonstrate their high genetic quality by developing more attractive honest signals in substitute for their immune system's strength. These honest signals require testosterone, which simultaneously suppresses the immune system.
A meta-analysis revealed that evidence for a direct effect of testosterone on the expression of sexual traits and the suppression of immunocompetence was weak. It was found, however, that increased testosterone influenced parasite loads, indicating an indirect role of the hormone in immune function.
Hub AI
Parasite-stress theory AI simulator
(@Parasite-stress theory_simulator)
Parasite-stress theory
Parasite-stress theory, or pathogen-stress theory, is a theory of human evolution proposing that parasites and diseases encountered by a species shape the development of species' values and qualities, proposed by researchers Corey Fincher and Randy Thornhill.
The differences in how parasites and diseases stress people's development is what leads to differences in their biological mate value and mate preferences, as well as differences across culture. Parasites causing diseases pose potential ecological hazards and, subsequently, selection pressures can alter psychological and social behaviours of humans, as well as have an influence on their immune systems.
Several hypotheses have attempted to explain how parasite load influences female mate choice, as certain traits are thought to be costly and the expression of such traits may be indicative of genetic quality.
According to the Hamilton–Zuk hypothesis, female mate choice is based on the extent to which male secondary sexual characteristics are expressed, as these are thought to be indicative of a heritable resistance to pathogens. A meta-analysis reviewed studies exploring the magnitude of the relationship between expression of secondary sexual characteristics and parasite intensity, as well as level of host immune functioning. Consistent with the hypothesis proposed by Hamilton and Zuk, the meta-analysis revealed that males with the fewest parasites and/or the strongest immune systems typically had the most extravagant secondary sexual characteristics. With regards to parasite-stress theory, these findings would be interpreted as those men who have encountered more parasites – or are naturally less capable of dealing with parasites – are also less desirable mates to females, due to a lower genetic quality for the potential offspring.
The Zahavi handicap principle, originally proposed by Zahavi in 1975, suggests that males who possess secondary sexual characteristics which provide a handicap are more attractive to females. These sexual ornaments are sexually selected in order to appear stronger and better adapted, compared to other males in the environment. This is because these characteristics are indicators of good genes and heritable viability, as they are costly to an individual's survival to maintain and produce. Therefore, the stronger the individual is, the more able they are to bear this cost.[citation needed]
These kinds of characteristics are a form of communication within species, as they are defined as honest signals (a signal about a mate's quality which cannot be faked). As a weak individual would not be able to survive with this particular characteristic, it signals to potential mates that it is stronger than its competitors and has a high mate value. Examples of such traits include the peacock's tail, very bright in nature and hence attracting more attention from predators as well as requiring more energy to maintain. Another example is the gazelle's stotting behaviour, whereby the gazelle jumps up and down when it spots a predator, in order to indicate its physical fitness.
This hypothesis takes Zahavi's principle further in suggesting that testosterone is responsible for the production of male secondary sexual traits while also suppressing the immune system. It therefore proposes that these traits are honest signals of mate quality because only males with 'good genes' should be able to fully express them without being vulnerable to parasite attack. Males will, therefore, demonstrate their high genetic quality by developing more attractive honest signals in substitute for their immune system's strength. These honest signals require testosterone, which simultaneously suppresses the immune system.
A meta-analysis revealed that evidence for a direct effect of testosterone on the expression of sexual traits and the suppression of immunocompetence was weak. It was found, however, that increased testosterone influenced parasite loads, indicating an indirect role of the hormone in immune function.