The tests showed that, when untended by people, all four species of crop did badly.
Here, humpback whales frolic for much of the winter months and four species of dolphin can be seen year-round.
Researchers worked out the entire genetic code of four species of tapeworm parasite.
Dr Mark Welch and Dr Meselson looked at this phenomenon in four sorts of gene in individuals from four species of bdelloid.
Marwell Zoo has become home to a further four species of Partula tree snail, which originate from islands in the Pacific Ocean and are extinct in the wild.
In parts of Puerto Rico, for example, there are places where researchers used to hear four species at once and they are now hearing one or two, a subtle but important change.
However you decide to pronounce it, there are four species of tapir -- all of which, as adults, become delightfully ugly and sort of look like 500-pound versions of Watto from Star Wars.
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Britain has a total of six deer species, four of which were introduced since Norman times.
Only four of the 56 species studied in the UK Butterfly Monitoring Scheme saw an increase in population size.
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Socially, only four of the 15 species are known to form groups that last for more than a year.
These curious hominids lived about two million years ago in an era that scientists consider the crucible of human evolution, when four or more apelike hominid species struggled for survival in Africa.
The companies are a bit cagey about the details, but according to Robert Dorsch, who works on the DuPont side of things, and Ray Chandra, of Genencor, the technology involves inserting four genes taken from various species of bacteria and yeast into industrial strains of E. coli.
At my restaurant Kin Shop, which focuses on contemporary Thai food, I've started a Monday night crab dinner series, highlighting at least three different species of crab spread over four courses.
In those areas that have had three or four periods of experimental burning only half the number of species of tree seedlings originally found are still there.
In contrast, it took carbon-based life forms (us) four billion years to evolve from the humble amoeba to a species capable of imagining and creating Watson.
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Or, rather, it was a species 50 years ago, but it is now heading rapidly towards becoming at least four of them.
And four other great die-offs have been identified - one of them killing off something like 90% of species.
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