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“Members of the same species” are sometimes defined as those who could mate and whose children could then produce offspring. If we could import one of our ancestors from x years into the past and mate them with someone alive now, how great a number could x be before that second-generation reproduction would fail? The result of subtracting that number from 2017 would be a way to express, more or less, the year of the evolutionary arrival of humans.

Obviously that test can’t be run and might be ethically iffy if it could, but Steve has heard rough guesses by experts range from 100,000 years to 250,000.

Hundreds of thousands of years we’ve existed as a species, and the first picture of the south pole of Jupiter was taken six months ago.

Here it is:

• Article at NASA