Why are neanderthals considered a different species?

Neanderthals are considered a different species because while some Homo sapiens interbred with Neanderthals, the numbers were few. Also, the crossbreed is very different and far off. It's like saying you'll cross a dolphin and a monkey to get a donkey, which doesn't work or make sense. 

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Essential for a scientist to do for credibility

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.