Irrational fears suggest a similar evo­

their feeding trough in their mouths

lutionary mechanism. "What are people

and pull back on it, or kick the door, or

phobic about, even in big cities?" Rapo­

dig holes in the ground," Dodman says.

port asks. "Not guns or cars, but snakes

Bears, on the other hand, will pace their

and spiders. You can condition a fear

cages; parrots pick their feathers out.

stimulus in monkeys after one exposure

Even tail chaSing, a common dis­

to a snake, but never to a flower." The

placement in many dogs, can take on a

same applies to the common human

pathological color. A remarkable case

Mother's Little Favorite A spiteful gene ensures,

"Like mother, like child"

I

n the words of one hymn to moth­ erhood, "M is for the many things

she gave me." If Mom is Tribolium castaneum, the flour beetle, one of her gifts had better be a gene called Medea.

disgust for insects. "In one study the re­

was reported recently in Canada, where

searcher put a sterilized cockroach in a

police dogs are trained to attack on

glass, took it out and offered $5 to any

command but to desist when the sus­

student who would drink from the

pected criminal raises his hands above

As three Kansas entomologists have

glass. Many of them wouldn't."

his head. "A suspect was threatening a

learned, if a female beetle carries

Yet not all animal compulsions can

policeman by holding a chair above his

Me­ dea, any of her offspring that lack the

gene will die in the cradle.

be compared with OCD, cautions Nicho­

head, and when the policeman told the

las H. Dodman, a veterinarian at Tufts

dog to attack, the animal just blew a

Its discoverers puckishly declare that

University. Stereotyped behaviors some­

fuse," Dodman says. "It started chasing

Medea is an acronym for "maternal ef­ fect dominant embryonic arrest," but

times reflect the stress of confinement,

its tail and wouldn't stop. Nothing could

which can stimulate the release of en­

cure it, so they finally had to put the

don't be fooled: their real inspiration

dorphins. These hormones, like the opi­

dog down."

was Medea of Greek mythology, who

ates they resemble, excite rather than

People, too, blow fuses when placed

relax certain animals. To work off their

in unbearable situations. Whether or not

killed her children in a jealous rage.

Me­ dea seems to represent the first mem­

angst, stir-happy animals often engage

such breakdowns themselves reflect a

ber of a previously unnoticed class of

in mindless activity, a solution etholo­

process of natural selection remains a

so-called selfish genes. Such genes may

gists call displacement. "Horses will grab

mystery.

play an important part in evolution and

-Philip E. Ross

the origin of new species. Selfish genes are paraSitic sequences of DNA that increase their own fre­

DNA Fingerprinting Reconsidered (Again)

W

hen the National Research Council published its study on DNA

quency in a population, usually to the detriment of the organisms that carry them. Although most genes can pros­

technology in forensic science in April, the New York Times report­

per only by contributing to the well-be­

ed that the panel had urged a moratorium on the use of DNA fin­

ing of their bearers, "there are certain

gerprinting as evidence in court. Victor A. McKusick, who headed the panel,

times in the life cycle of an organism

was quick to deny the report. The Johns Hopkins University human geneti­

when genetic elements can potential­

cist insisted that his group still endorsed the technique, although it did call

ly cheat and gain a transmission ad­

for stricter controls on its use.

vantage," explains Jack H. Werren, who

Even so, defense lawyers are using some of the research council's less well­ publicized conclusions to try to overturn convictions won on the basis of

studies selfish genes at the University of Rochester.

DNA fingerprinting evidence. "We' re going to attempt to get lawyers in every

Some genes cheat by inserting extra

state to look at every relevant case," vows Barry C. Scheck, a prominent de­

copies of themselves into cells; some

fense lawyer and professor at the Cardozo School of Law in New York City.

cripple or obliterate their genetic coun­

One of the recommendations of the panel that has attracted the attention

terparts on other chromosomes. A few

of attorneys is that fingerprinting tests showing a phenomenon called band

can even change the sex of their host

shifting be declared "inconclusive" until laboratories have performed ade­

so that it produces only eggs or sperm

quate studies on the effect. Band shifting can make two forensic samples

favorable to the gene's distribution. Vir­

from different biological sources appear the same; private companies that

tually all species, including humans, har­

perform DNA fingerprinting and the Federal Bureau of Investigation have al­

bor at least some selfish genes. "It's a

ready made attempts to correct for it. But the McKusick panel was not con­

jungle in there," Werren quips.

vinced that such attempts protect those accused: a suspect could be wrong­

Medea is remarkable because it is the first maternally linked selfish gene that

ly convicted if the "correction" was itself in error. Scheck, who is co-chair of a committee that is reviewing old convictions in

acts on embryos rather than ova or

the light of the research council's report, believes that many people have been

sperm. Richard W. Beeman of the Agri­

convicted on the strength of DNA fingerprinting tests that showed band shift­

cultural Research Service in Manhattan,

ing. One company offering DNA fingerprinting, Lifecodes, concludes that 30

Kan., and his colleagues Kenlee S. Frie­

The research council study also recommended that in the future a new,

University became aware of Medea while

percent of the forensic tests it has performed showed the effect.

sen and Rob E. Denell of Kansas State

safer mathematical technique be used to interpret the results of DNA tests,

testing whether flour beetles from dif­

and it outlined how the technique should be performed. That recommenda­

ferent parts of the world had any prob­

tion is likely to be grounds for reopening many cases in which the old tech­

lems breeding with one another. When

nique was used to secure convictions, Scheck says. A brief arguing against the admissibility of DNA evidence that cites the re­

they tried to cross beetles from a rice

search council's report has now been filed in a "consolidated" case in the

a farm in Georgia, they noticed that

District of Columbia, U.S. v. Porter. The case is being appealed by the gov­

some of the hybrid combinations had

cluded. Similar briefs in California and Chicago are likely to follow quickly,

resulting larvae died before or during

Scheck predicts.

hatching.

ernment because DNA fingerprinting tests carried out by the FBI were ex­

-Tim Beardsley

warehouse in Singapore with ones from

consistently small broods: many of the

Further experiments, which Beeman,

26

SCIENTIFIC AMERICAN July 1992 © 1992 SCIENTIFIC AMERICAN, INC