Science Fair Project Encyclopedia
In zoology, a hermaphrodite is a species that contains both male and female sexual organs at some point during their lives. In many species, hermaphroditism is a normal part of the life-cycle. Generally, hermaphroditism occurs in the invertebrates, although it occurs in a fair number of fish, and to a lesser degree in other vertebrates.
See below for use of the term in plants.
Note: The term "hermaphrodite" has historically been used to describe people with ambiguous genitalia or biological sex. The term intersexual to describe these people is now preferred, and the term "hermaphrodite" is deprecated, since hermaphrodism is not a typical part of the human life cycle.
- Sequential hermaphrodite: The organism is born as one sex and later changes into the other sex.
- Protandry: When the organism starts as a male, and changes sex to a female later in life. Example: The seabasses (Family Serranidae). These are a highly sought food fish complex made up of primarily groupers. Since even a small male can produce more than enough sperm to fertilize a huge number of eggs, while a female's egg output increases greatly with an increase in size, this strategy makes sense for an organism (fishes in general) where over 90% of the eggs laid will not result in a fish that reaches sexual maturity. It has been shown that fishing pressure actually is causing a change in when the switch from male to female occurs, since fishermen naturally prefer to catch the larger fishes. The populations are generally changing sex at a smaller size, due to natural selection.
- Protogyny: When the organism starts as a female, and changes sex to a male later in life. Example: Wrasses (Family Labridae) are reef fishes that tend to have three distinct sexual types. Small females, immature males and supermales. The small females and the immature males have identical colorations. The supermale is usually brightly colored, and there is only one in a given area of the reef. This supermale dominates the other wrasses of the species, having the choice of females to mate with. When the supermale dies, the largest wrasse in the area, male or female, becomes the new supermale.
- Simultaneous hermaphrodite: The organism has both male and female sexual organs at the same time as an adult. Usually, self-fertilization does not occur. Also called synchronous hermaphrodites. Examples: Earthworms. Hamlets (Family Haemulidae) are a type of fish that are curious for many reasons, including that they seem to be evolving into different species quite rapidly. Unlike other fishes, hamlets seem quite at ease mating in front of divers, allowing observations in the wild to occur readily. They do not practice self fertilization, but when they find a mate, the pair takes turns between which one acts as the male, and which acts as the female, through multiple matings, usually over several nights.
Gonadal dysgenesis, a type of intersexuality formerly known as "True Hermaphroditism", occurs in about one percent of mammals (including humans), but it is extremely rare for both sets of sexual organs to be functional, usually neither set is functional. In many cases, these manifestations are altered, sometimes only cosmetically, to resemble standard male or female anatomy shortly after birth.
Hermaphrodite is used in botany to describe a flower that has both staminate (male, pollen-producing) and carpelate (female, seed-producing) parts. Other terms for this condition are bisexual and perfect. Hermaphrodism in plants is more complex than in animals because plants can have hermaphroditic flowers as described, or unisexual flowers with both male and female types developing on the same individual—a closer analogy to animal hermaphrodism. However, this latter condition constitutes monoecy in plants, and is especially common to the conifers, while occurring in only about 7% of angiosperm species (Molnar, 2004).
The term "hermaphrodite" derives from Hermaphroditus, the son of Hermes and Aphrodite in Greek mythology, who was fused with a nymph, resulting in one being possessing physical traits of both sexes. Thus Hermaphroditus was, by the modern terminology, a simultaneous hermaphrodite. The mythological figure of Tiresias, who figures in the Oedipus cycle as well as the Odyssey, was a sequential hermaphrodite, having been changed from a man to a woman and back by the gods.
- Molnar, Sebastian. 2004. Plant Reproductive Systems, internet version posted February 17, 2004.
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