What makes two species different?

Most evolutionary biologists distinguish one species from another based on reproductivity: members of different species either won't or can't mate with one another, or, if they do, the resulting offspring are often sterile, ...

InSight places first instrument on Mars

NASA's InSight lander has deployed its first instrument onto the surface of Mars, completing a major mission milestone. New images from the lander show the seismometer on the ground, its copper-colored covering faintly illuminated ...

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