While some avian species have very long phallus, like the duck, whose penis grows as big as its own body, others have none. Current biology published that 97 % of avian species stop growing their penises as early embryos. As humans, we think that internal fertilization is the way to go, because without it, we wouldn´t go too far, in terms of reproducing.
Darwin at some point wondered about the changes in shape of bird beaks from island to island. He found that the beaks adapt to survive on available food.
The birds have genitalia when are embryos, but after nine days the penises stop growing and start shrinking. According with Current Biology, the responsible for this in 97% of birds is a gene, which plays a very important role, is the activation of cell death by Bmp4 in the genital tubercle.
The team research two types of birds: the Galliformes, which go on land and have a lack of genitalia; and the Anseriformes, which is the water friendly and have a big genitalia, which means that the Bmp4 makes it grow and grow and grow. The breakthrough found also, that Bmp is related to beak shape, feathers, and toothless.
For Darwin all species are coming from one ancestor and the changes are related to evolution. Darwin considered “natural selection” like a struggle and a race, and at the end of it the fittest wins. He also called it “struggle for existence”, competition among species related is more severe and gets rough. However it´s not clear why some birds lost their penises, commented Ana Herrera, the lead author of the study, but the loss of the genitalia might have given the hens more control over reproduction. Bob Montgomerie an evolutionary biologist, commented to Nature that because the cloacal kiss needs cooperation between willing partners, female chickens and other birds may have selected males with smaller penises to escape forced copulation.
In the “struggle for existence”, the Bmp4 is on and off in some species, is the regulation between cell proliferation and cell death. Martin Cohn of Howard Hughes Medical said, “Too much cell division or too little cell death can lead to overgrowth or miss-regulated growth, as in cancer”
In the absence of genitalia, Galliformes develop a fertilization method that doesn´t need penetration. The males and females have an orifice known as cloaca. When male and female rub each other, the sperm is transferred to the female reproductive tract. This is known as a “cloacal kiss”.
This new discovery is transcendental because allow us to understand why species evolve in certain way. This breakthrough shows us the possible cause of malformations and at the same time, might answer some medical questions.
By Oskar Guzman.
Source: BBC news, Nature, National Geographic.