Hermaphroditism in biology and nature

Hermaphrodite is an organism in which a single individual has both male and female gametes. Many plants and some animals are naturally hermaphroditic and can self-fertilize and reproduce themselves from a single organism. (Omoto & Lurquin, 2004, p. 209) While some species actually reproduce asexually, such as single celled organisms and other creatures, this is not the same as being hermaphrodite. There are benefits to the species in some sense in being able to self-fertilize and reproduce in this way. Sexual reproduction in effects cuts the population's growth rate in half. Only females produce offspring, not males. If half the population is male, then the speed of population growth is half that of an all-female population. An all-female species can quickly out produce a male/female species, allowing an all-female species to survive in high mortality habitats where a male/female species can't succeed. This result is also true in hermaphrodite species, in which the fifty-fifty allocation of reproductive effort to male and female function reduces the female allocation used to make eggs by half. (Roughgarden, 2004)

A single organism that makes both small and large gametes at some point in life is called a hermaphrodite. An individual who makes both sizes at the same time is a simultaneous hermaphrodite, and one who makes them at different times is a sequential hermaphrodite. Most flowering plants are simultaneous hermaphrodites because they make pollen and seeds at the same time. Pollen is the male part of a plant and the ovule is the female part. A pollinated ovule turns into a tiny embryo that detaches, to be blown away by the wind or carried away by an animal. Among animals, hermaphrodism is common in the ocean. Most marine invertebrates, such as barnacles, snails, starfish, fan worms, and sea anemones, are hermaphroditic. Many fish are as well. (Roughgarden, 2004)

Hermaphrodism can also be an asset to the geneticist is another way. Take for instance the nematode Caenorhabditis elegans, which has been a staple of developmental biology research since the 1960s. It has come to be the geneticist prime target in genomic experimentation and research, in large part because of its relative simplicity and its straightforward developmental evolution. Additionally it is a mostly transparent roundworm, a benefit for researchers wishing to keep track of which cells end up where. Indeed, studying its development in a stepwise fashion seems so straightforward that it has been referred to it as "the reductionist's delight." (Kaplan, 2006) C. elegans has two forms, a hermaphrodite and a male form. The adult hermaphrodite has 959 somatic cells; of these, 302 are neurons, making its nervous system by far its largest organ. (Kaplan, 2006) it's hermaphroditic nature, as previously discussed, also makes it an ideal candidate for quick reproductive genetic research. C. elegans hermaphrodites are able to reproduce either by sell-fertilization, using sperm that have been made during larval development, or by cross-fertilization, using sperm contributed by a male after mating. Hermaphrodites are unable to cross-fertilize each other. Once a hermaphrodite has mated with a male, the sperm from the male are used preferentially over the sperm made by the hermaphrodite. This form of self-fertilization means that a hermaphrodite carrying a recessive mutation will automatically produce animals homozygous for that mutation, as one-quarter of its progeny, according to standard Mendelian principles. As a result, screening for mutants is made much easier, because there is no need to set up specific crosses in order to generate homozygotes. (Hope, 1999; Kaplan, 2006)

Normally, populations of this animal consist almost entirely of diploid self-fertilizing hermaphrodites. which each produce a limited number of sperm and a larger number of oocytes. Both types of gametes result from conventional meiosis with about one crossover event per chromosome. (Hope, 1999, p. 247)

In higher order species such as animals and humans, "hermaphroditism" is the technical term denoting the presence of both testicular and ovarian tissue. Within the human species, an individual organism is a true hermaphrodite when it possesses, "a DNA chromosome karyotype of 46 XX/XY (mosaic) independently of one's external appearance. Hermaphrodites have two separate chromosome karyotypes, similar to Siamese twins sharing one body. This can happen when two fecundated gametes merge." (Corazza, 2004, p. 368)

True hermaphrodism in human beings does not exist, but pseudohermaphrodism does, where an individual has both male and female external genital organs, sometimes at the same time. This condition has been met with various degrees of shock and confusion by most people, doctors included. Surgeon Franz Neugebauer also believed that, in addition to being a fairly regular problem, pseudohermaphrodism was a particularly serious problem.