In The Origin of Species , he devoted a chapter to hybrids, but their existence was a riddle he never really solved. Hybrid animals like mules, Darwin noted, are usually sterile.
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He deemed it a "strange arrangement" that nature would afford two species the "special power" to create hybrids but then prevent these offspring from propagating. Darwin asserted that hybrids might inadvertently push back the evolutionary clock, resurrecting traits that were better left behind. He used the mixing of human racial groups as an example, stating that foreign travelers frequently remarked on "the degraded state and savage disposition of crossed races of man. Darwin's hybrids-are-bad dictum became orthodoxy during evolutionary biology's "modern synthesis," in the s and '40s, which firmly connected genetics to natural selection.
Harvard ornithologist Ernst Mayr, a leading neo-Darwinist, set the tone by dismissing hybrids as an evolutionary dead end. Mayr's verdict involved a surprisingly contentious question: What exactly is a species? Darwin had seen it as an arbitrary designation for animals that have similar physical features.
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Mayr came up with a concrete definition known as the "biological species concept. But maybe they aren't. Arnold is part of a growing camp that sees species as more liquid than solid, and he rejects the idea that hybrids are always evolutionary losers just because they often can't reproduce. Arnold is pushing a profound reconceptualization of evolution, one in which hybrids are more than bit players. Forget the tree of life, with new species neatly branching off from a common ancestor. It's a web of life, and hybrids help genes flow in unexpected directions.
But what about their famous sterility? Some hybrids can reproduce, and Arnold stresses that rare events have an "overwhelming importance" in the evolutionary process. This process appears to be under way right now in the U. And some scientists contend that matings between gray wolves and coyotes thousands of years ago created an entirely new species: the red wolf. More commonly, though, hybrids mate with one of their parent species, influencing the mix of what gets passed along to subsequent generations; essentially, they provide a bridge for genes to cross the species divide.
In a paper about hybridization and primate evolution that Arnold co-wrote last year for the journal Zoology , he offers several examples, including chimpanzees and bonobos. DNA studies suggest that these two great apes swapped genes sometime after separating from a shared ancestor at least , years ago. Arnold believes these ape cousins occasionally mated but that the resulting "bonanzees" did not establish a new species.
Instead, they hooked up with either chimps or bonobos. Bonanzees ultimately vanished, but they left genetic footprints in the genomes of their descendants. In addition to comparing genomes for evidence of unusual gene flow, scientists increasingly are using DNA analysis to confirm the existence of heretofore unknown natural hybrids, whose existence argues that this process still occurs. On April 16, , a hunter in Canada's Northwest Territories shot a polar bear whose fur had an orangish tint.
Research showed that this animal had a grizzly bear father, making it the first confirmed wild pizzly ever found. Pizzlies had been bred before in captivity. In , DNA analysis done by the Forest Service confirmed that five odd-looking felines found in Maine and Minnesota were bobcat-lynx hybrids, dubbed blynxes. How much, then, do hybrids contribute to evolution?
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Nobody really knows. That's what's so exciting about these new DNA discoveries: The story is still unfolding. Some are astonishingly beautiful. In Ramona, California, Nancy Nunke raises zorses and zonkeys at a six-acre spread called the Spots 'N Stripes Ranch, which mainly exists to breed zebras and miniature horses for show and for sale to private animal owners. After I pass through a security gate, Nunke greets me at her house and then points out her one zorse and two zonkeys, who are peeping at us from nearby corrals.
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Nunke introduces me to her zorse, Zantazia, which, at seven months old, is still a zoal. This delicate creature has a sorrel coat, a horse's long and thin face, and white stripes on her head, neck, torso, and legs.
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The offspring of a quarter horse mother and a Grevy's zebra father, she may end up standing taller than both. I reach out to stroke Zantazia's neck, but she backs away. Nunke says zorses and zonkeys are friendly, but they have to set the pace. Nunke has a soft spot for all "stripeys," which she thinks are more playful and affectionate than horses. The z is totally in them. We walk over to meet the zonkey brothers, Zane and Zebediah, who have donkey faces and ears, caramel coats, and a dizzying array of black lines.
Zane brays, and he looks so much like a zebra that his hee-haw startles me. Nunke says some purists believe it's wrong to breed hybrids, that they pollute the natural order. In , Ilya Ivanovich Ivanov, a Russian pioneer in artificial insemination, proposed seeding a female chimpanzee with human sperm. At a zoology conference in Austria, he noted oh-so quaintly that this method would avoid the ethical dilemma of forcing the two species to actually have sex. Sixteen years later, with the backing of the Soviet Academy of Sciences, Ivanov traveled to Africa and gave it a try.
The details of Ivanov's experiments only came to light in , when a Rus-sian science historian, Kirill Rossiianov, produced a page paper about the work. The study was published in English in the journal Science in Context , and when I came across it I was astonished. I struck up an e-mail correspondence with Rossiianov, then, late last year, met with him in Moscow. Over a ten-year period, Rossiianov was able to unearth Ivanov's diaries and lab notes from the Soviet archives. According to Rossiianov, Ivanov and his son, a biochemistry student, set up a lab at the botanical gardens near Conakry, French Guinea.
On the morning of February 28, , they wrapped two female chimps in nets and inseminated them with sperm from a local man. On June 25, they inseminated another chimp with human sperm, this time using a special cage and knocking her out with ethyl chloride. None of the three became pregnant. Rossiianov, a shy man, told me Ivanov's work repulsed him.
Even now I find it terrible difficult to understand. And Ivanov had plans to take things further. I went to a nature habitat once and there was one behind a glass window. It jumped up towards me and placed its left and right fingers on the edge of its mouth and stuck its tongue out at me.
Then, its buddy came over to him and started mimicking him. It was the funniest thing—ever since then, I was in love with them. CW — My favorite zoo animal is the penguin , that is all. Dylan — My favorite zoo animal is the wolf --because the Starks of Winterfell are cool, and wolves eat meat just like me. Jandy — When I go to the zoo, I love watching the seals and sea lions as well as talking to the birds in the aviary.
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I have fond memories of growing up in NJ and visiting Turtle Back Zoo back when they would allow small children to ride the turtles. Now that I reside in Missouri, we have the best zoo in the country—the St. Louis Zoo! Jo Ann — My favorite zoo animals are the Monkeys!
I like to watch them interact with one another. I also really love horses , although they are not considered zoo animals. Joe — My favorite zoo animal is the penguin! John — Admittedly, I am not much of a zoo person. However, if I had to choose an animal, I think it would be an Emu ; and it would probably be in the context of a safari. I like being around animals when they have more space.
Ken — I like the chimps , orangutans and monkeys. For some reason, I feel most at home at the zoo, when I am around them! I also like all the animals on the New Zoo Revue , of course! Kris — My favorite zoo animals are the big cats —the regality of lions and tigers portray sheer strength! Laurie S. I have a collection of over stuffed figurines and collectables. Laurie T. They are quite cute! It's fascinating to just hang out and observe their "human" behavior and interactions.
Conversations, nurturing, playfulness— it's all there! Melissa — My favorite zoo animals have always been penguins. I think they are adorable, and I love their little waddle. My new favorite zoo animal, thanks to my son, is the giraffe. He absolutely loves them! We have tons and tons of giraffe stuffed animals at home. My son just loves watching them…probably because they are so tall!
Nina — My favorite zoo animal must be monkeys.
My first memory of visiting the zoo was The Bronx Zoo when I was a child. I was so impressed with the gorilla ; I still remember him sitting there.