Penis fencing
Encyclopedia
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
behavior engaged in by certain species of flatworm
Flatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
, such as Pseudobiceros hancockanus
Pseudobiceros hancockanus
Pseudobiceros hancockanus is a species of hermaphroditic flatworm in the family Pseudocerotidae.-Description:According to the Baensch Marine Atlas, "P. hancockanus is intense blue to black with white and orange peripheral bands and a purple fringe. The two short cephalic antennaie are easily...
. Species which engage in the practice are hermaphroditic
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
; each individual has both egg-producing ovaries and sperm-producing testes.
The flatworms "fence
Fencing
Fencing, which is also known as modern fencing to distinguish it from historical fencing, is a family of combat sports using bladed weapons.Fencing is one of four sports which have been featured at every one of the modern Olympic Games...
" using two-headed dagger
Dagger
A dagger is a fighting knife with a sharp point designed or capable of being used as a thrusting or stabbing weapon. The design dates to human prehistory, and daggers have been used throughout human experience to the modern day in close combat confrontations...
-like penises which are pointed, and white in color. The mating ritual involves a violent battle during which two hermaphroditic flatworms attempt to pierce the skin of one another with one of their penises. The "winner" is the organism that inseminates the other; the winner becomes the father. The sperm is absorbed through pores in the skin, causing fertilization in the "loser," who becomes the mother.
Child-bearing, while necessary for the continuation of a species, requires a considerable investment of time and energy from one or both parents
Parental investment
In evolutionary biology, parental investment is any parental expenditure that benefits one offspring at a cost to parents' ability to invest in other components of fitness...
, and according to Bateman's principle
Bateman's principle
In biology, Bateman's principle is the theory that females almost always invest more energy into producing offspring than males invest, and therefore in most species females are a limiting resource over which the other sex will compete...
, almost always more from the mother. Thus, from a biological point of view, it is preferable to be the father rather than the mother. However, there are other hermaphroditic species where both partners try to be inseminated rather than to inseminate.