Sunday, January 21, 2007

Lighthouse of Alexandria

The Pharos of Alexandria was a lighthouse built in the 3rd century BC on the island of Pharos in Alexandria, Egypt to serve as that port's landmark, and later, a lighthouse. With a height variously estimated at between 115 and 135 metres it was among the tallest man-made structures on Earth for many centuries, and was identified as one of the Seven Wonders of the World by classical writers. It ceased operating and was largely destroyed as a result of two earthquakes in the 14th century AD; some of its remains were found on the floor of Alexandria's Eastern Harbour by divers in 1994. More of the remains have subsequently been revealed by satellite imaging.

Constructed from large blocks of light-colored stone, the tower was made up of three stages: a lower square section with a central core, a middle octagonal section, and, at the top, a circular section. At its apex was positioned a mirror which reflected sunlight during the day; a fire was lit at night. Extant Roman coins struck by the Alexandrian mint show that a statue of a triton was positioned on each of the building's 4 corners. A statue of Poseidon stood atop the tower during the Roman period.

Monday, January 08, 2007

Conjoined twins

Conjoined twins are monozygotic twins, whose bodies are joined together at birth. This occurs where the single zygote of identical twins fails to separate completely, and the zygote starts to split after day 13 following fertilization. This condition occurs in about 1 in 50,000 human pregnancies. Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as brain, heart or liver.

A chimera is an ordinary person or animal except that some of his or her parts actually came from his or her twin. A chimera may arise either from identical twin fetuses, or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin colouration in human chimeras. A chimera may be a hermaphrodite, composed of cells from a male twin and a female twin.

Monday, January 01, 2007


The term wildlife refers to living organisms that are not in any way artificial or domesticated and which survive in natural habitats. Wildlife can refer to flora but more usually refers to fauna. Wildlife is a very general term for life in ecosystems. Deserts, rainforests, plains, and other areas including the most built-up urban sites all have distinct forms of wildlife.

Humans have historically tended to split civilization from wildlife in a number of ways; besides the obvious difference in vocabulary, there are differing expectations in the legal, social, and moral sense. This has been a reason for debate during recorded history. Religions have often declared certain animals to be sacred, and in modern times concern for the environment has aggravated activists to protest the exploitation of wildlife for human benefit or entertainment. Literature has also made use of the traditional human separation from wildlife.