Reader question:
In the intro to this story (Did Humans Cause Extinction of the Alaskan Horse? New Scientist, May 2, 2006) - A statistical evaluation of fossil findings suggests the Alaskan species may have vanished later than thought, meaning humans have no alibi - what does "humans have no alibi" mean? Does it mean that humans killed the horses in Alaska?

My comments:
Humans may not have slain every one of the Alaskan horses by hand, but they cannot reasonably escape responsibility for the extinction of the ancient species, either. That is what's meant by "humans have no alibi".

Here's how the rest of the story reads:
"Previous dating of the youngest fossils indicates the horses disappeared about 500 years before the arrival of humans from Asia. But a new statistical analysis of the fossil dates suggests the animals actually went extinct a few hundred years after humans turned up.

"The end of the Pleistocene epoch saw extinctions of many large animals, including mammoths and caballoid horses in North America and elsewhere. Exactly what caused some these extinctions remains open for debate. But experts consider climate change and human hunting two of the most probable explanations."

In other words, even though without conclusive evidence that humans hunted the horses to extinction, the fact that they disappeared hundreds of years after humans emerged deprives the two-legged mammals their greatest defense - an easy excuse in the form of an alibi. Humans can not say: "We didn't do it because we were elsewhere when it all happened."

The term alibi, which comes from Latin meaning "elsewhere", is a common legal term used as a defense by the accused to suggest that they could not have committed the crime in question because they were at somewhere else than the scene of crime when it took place.

In the court of law, when a defense produces an alibi, the prosecutor must prove the alibi to be false, or the accused will be set free via alibi.

This, from the BBC (Court hears Archer 'confession', June 15, 2001):
"Telephone calls between (millionaire novelist) Lord Archer and his friend Ted Francis, taped by a newspaper in an attempt to get him to confess to making up a false alibi, have been played to an Old Bailey (the central criminal court in London) jury.

"Mr Francis told News of the World reporters how Lord Archer had asked him for a false alibi for the night he was accused of having sex with prostitute Monica Coghlan, the court heard.

"The date of the alleged sexual liaison was later changed and the Francis alibi was not needed in the 1987 libel trial in which Lord Archer won ?500,000 damages...

"Mr Francis had told him (Archer): 'I said I would give him an alibi (that the two of them were together having dinner that particular night) for his wife but I would not lie in court for him.'"
...

Mr Archer, as UK newspapers are wont to address male figures in the news, was later found guilty of perjury (lying in court) and perverting the course of justice and jailed for four years. Mr Francis was acquitted of perjury after saying the false alibi he gave was to protect Archer's marriage.

In everyday language, an alibi is also often used to mean "an excuse", and usually with a negative connotation because excuses, as it were, are usually not "good" excuses. When you say, for example, that every day, someone has a new alibi for not getting the job done, it means you don't think any of their excuses given are valid reasons.

Here are a few more examples to put "alibi" into context:
1. If you think that lifelong learning and society-ready graduates are just empty phrases coined for a report on teaching, to be used as an alibi for doing business as usual, think again (Lifelong Learning, by Randy Weckman, http://www.ca.uky.edu).

2. In 19th century Australia, religion and race became synonymous in the language of prejudice and discrimination. Religion provided an alibi. It hid racism under an acceptable antipathy to a religion and culture considered to be fundamentally alien to our Australian values and way of life. And religion provided a shelter and a solace for those who felt excluded or persecuted. Racism, prejudice and resentment grew into a mutual antipathy that scarred Australia for generations (http://www.laborfirst.com.au).

3. Beer is the excuse these people need to behave differently, and gives them an alibi if they do anything stupid in the process. Thus their alcohol-induced stupidity doesn't take away from their inherent "koolness"-the beer made them do it! (Have a Sip from the Beer of Deceit, http://www.bradezone.com).

Now, I'd like to end this column with a serious question. What's your alibi for everything (from being fat or being thin)?

Well, if you have no alibi, you'd better have no complaint, either.

Zhang Xin is Trainer at chinadaily.com.cn. He has been with China Daily since 1988, when he graduated from Beijing Foreign Studies University. Write him at: zhangxin@chinadaily.com.cn, or raise a question for potential use in a future column.