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Many fish, amphibians and reptiles — have lots of reproductive tricks. 1) ___ can store sperm for a long time, tiding them over when conditions may be poor for reproduction. Another trick is the natural ability to clone. DNA analysis of seeming “miracle embryos” show that every bit of their 2) ___ simply came from the female. Virgin birth, known to biologists as 3) ___ (from the Greek, “parthen” meaning virgin or maiden and “genesis,” beginning), has been seen in species over the years. Some lizards, like the Komodo Dragon, occasionally produce offspring by 4) ___. So do several species of fish, including a female hammerhead shark at the Henry Doorly Zoo in Omaha, Nebraska that produced offspring without a male in 2007. The shark example is particularly striking because sharks are very primitive living fish, having shared a common ancestor with us over 400 million years ago. Biological cloning is not a recent invention of scientists; it is an ancient ability, from nature. Sharks, fish and lizards are probably only the tip of the iceberg. We know of this 5) ___ cloning, only in those rare instances when we’ve been lucky enough to see it. Nobody knows how common it is because there has been no systematic search for the phenomenon. The big question that parthenogenesis raises is, if some females can get along without males, why does any species have males? The reason is that naturally cloned hatchlings are simply genetic duplicates of the mother. In a world of clones, there would not be enough variation for populations to adapt. Biological cloning is a great stopgap measure to ensure the survival of a species, but works against it in the long haul. Cloning is one of many mechanisms species use to 6) ___ in a dangerous world. Some reptiles do not determine gender genetically, but rely on different incubation temperatures to determine the development of males and females. Other creatures can actually switch gender during their lifetimes, being born male and developing as females. Still others can switch gender based on behavioral cues in the social group. However, without 7) ___, the world would be static and unchangeable, and species would gradually disappear as they failed to meet challenges like changing climates and environments.
ANSWERS: 1) Females; 2) DNA; 3) parthenogenesis; 4) cloning; 5) natural; 6) survive; 7) variation