And are we their offspring?

(For the latest Human Nature columns on tanning, junk food, and gay marriage, click here.)

We're the offspring of sex between human and chimp ancestors, according to the latest evolutionary theory. Fossils indicate our ancestors diverged from chimp ancestors 7 million years ago, but genes suggest we were still reproducing with them 6 million years ago. Solution: The two groups split but continued having sex, and we probably descended from the breeding of chimpoid-humanoid females with chimpoid males. Criticisms: 1) Would chimpoid-humanoids have been sterile, like mules? 2) Maybe we got the genetic math wrong. 3) It's too gross—our female ancestors would never have stooped to sex with knuckle-draggers. Rebuttals: 1) Women do this every day. 2) We're animals; deal with it. 3) This is the best explanation available until somebody comes up with a better one. (For Human Nature's take on sex between humans and dogs, click  here. For evolution vs. creationism, click here and here. For the latest fatal and near-fatal chimp attacks on humans, click  here  and here; for the superiority of altruism in humans over chimps, click here.)

Military contractors are planning to put battlefield surveillance technology on the Mexican border. Their bids are being solicited by the Bush administration to curtail illegal immigration. Examples: aerial drones, radar-wielding blimps, and cameras armed with software to analyze images. Arguments against this approach: 1) We tried stuff like this before, and it failed, which is why we're still debating this issue. 2) We blew a lot of money on it, so prove it works this time, or Congress won't shell out. Arguments for it: 1) We have to make it work, because border agents won't be enough. 2) This time we're going to think way outside the box, so it'll be really cool, trust us. (For Human Nature's take on how drones turn war into a video game, click here.)

"Therapy dogs" carry infectious diseases. They're brought into some hospitals to put patients in a better mood, but a study says 80 percent of the dogs have infections that could spread to humans, including salmonella and drug-resistant E. coli. Argument for the dogs: Because they're maintained for therapy, they're properly vaccinated and groomed to keep out parasites. Argument against them: Because they're dogs and because they're brought in for therapy, they're more likely to jump on a patient's bed and lick her face. And if the dog doesn't give her an infection, she can give him one to pass on to another patient. Illness, open wounds, compromised immune systems—what a great place to circulate animals. (For Human Nature's take on genetic engineering of dogs, click here. For the ethics of eating dogs, click here. For the ethics of sex with dogs, click here.)

Zanzibar ordered the prosecution of anyone whose home lacks a toilet. Cholera has killed at least 20 people and sickened at least 350 in the African nation since March. Civic leaders say "many impoverished villagers on the island usually relieve themselves in plastic bags and hurl them in the open or into waterways." A government representative told local officials to make sure people "use toilets and not flying toilets," and the country's health commissioner told officials to "take them to court if a home is without a toilet." The government is also urging Muslim clerics to get out the word that "the teachings of Islam emphasize cleanliness."

The U.S. is becoming a mecca for embryonic sex selection. The practice, in which clinics make multiple embryos and freeze or flush those of the wrong sex (e.g., all the girls if you want a boy), is banned in many countries. Thousands of couples from those countries are coming to the U.S. to have the procedure; more than half the clients at one clinic are foreign. Criticisms: 1) It's wrong to kill embryos just for being male or female. 2) If everyone does this, a shortage of women in China and India will cause social disaster. 3) What other harmless traits will we flush embryos for next? Defenses: 1) We don't flush most embryos; we freeze them. 2) Most Americans and Canadians want girls, so the selection evens out. 3) We believe in "reproductive choice"; if you don't like sex selection, don't do it. 4) Doing it at the embryonic stage is better than the common foreign practice of aborting female fetuses or killing baby girls. (For an update on the 500,000 Indian fetuses reportedly aborted each year for being female, click here. For Human Nature's previous takes on IVF bans and regulation, click here and here.)

New York City parents are fighting the mayor's ban on cell phones in schools. The city has confiscated hundreds of phones from kids; opponents of the ban have filed legislation in the city council and are threatening to sue. Mayor's views: 1) Schools are for learning, and phones are a distraction. 2) Kids are using phones to cheat on tests. 3) They're using phones to summon friends for gang wars. Parents' views: 1) For safety reasons, kids and parents should be able to communicate quickly, especially after 9/11. 2) The mayor just hates cell phones. 3) Why not let the kids keep the phones as long as they're turned off? Cynics' view: You can give poor kids a lousy education, but if you mess with rich parents, God help you.

Britain began weeding out embryos with cancer genes. A woman is carrying the first implanted embryo screened for inherited cancer. The gene in question leads to cancer in 90 percent of carriers; the clinic that made embryos from her genetic material (and apparently froze or discarded embryos that carried the gene) plans to screen other embryos for a gene that leads to breast cancer in 80 percent of carriers. Critics' argument: It's dangerous to start chucking embryos for having genes that might not lead to diseases, especially when the diseases don't begin for many years and can often be treated. Defenders' arguments: 1) If your family had one of these nasty genes, you'd get rid of it, too. 2) "This gives families a choice." (For an update on British government approval of embryo screening, click here. For Human Nature's takes on embryo screening and genetic engineering, click here and here.)

Alligators apparently killed three Americans this week. One victim died while snorkeling, but in the case of a Florida jogger, "A medical examiner concluded that the 28-year-old woman was attacked near the canal bank and dragged into the water." One killer gator, already captured, is 9 and a half feet long; another, at large, is estimated at nearly 8 feet. Explanation for the attacks: As it gets warmer, gators get hungry and mobilize to find prey. Official reactions: 1) Don't worry, gators killed only 17 people in 58 years until this week. 2) One of this week's victims may have been using drugs. 3) We'll catch the killers. 4) You can avoid attacks by staying out of water in "heavily vegetated areas" and not walking your dog near water in darker hours. Unofficial reaction: Land shark! Meanwhile, chimp attacks have increased, especially on children. Official reaction: "People are ultimately responsible for a situation in which the apes are being squeezed from their natural homes."

The universe is a potentially endless series of Big Bangs, according to a new theory. Most scientists think the universe began 14 billion years ago with the Big Bang and will keep expanding and scattering into nothingness. The new theory says a gap between the current theory's predictions and emerging data can be explained if the universe is at least a trillion years old, probably driven by a cycle of bangs. In fact, the authors say, there's no reason to assume its age is finite. Old forecast: We and our descendants will dissolve into smithereens, along with everything we've built and done. New forecast: We and our ancestors will be blasted into smithereens, along with everything we've built and done.