I often hear it’s humans, but what about bonobos?
Surely they are more closely related, or are they actually the same species with merely differing cultures?
My reading is that chimps and bonobos are different species, but closely related.
My personal experience at a zoo- the first time I saw a bonobo, it struck me as a very man-like chimp.
Most people would look at chimps and bonobos and see them as more closely related to each than humans. Just because two species in a group of three look more like each other than the third (furry, don’t make or fly airplanes) doesn’t necessarily make them more closely related.
But in fact, chimps and bonobos are more closely related to each other.
Here is an article.
The term “chimpanzee” is applied to both members of the genus Pan. P. troglodytes (common chimpanzee) is more closely related to P. paniscus (bonobo or pygmy chimpanzee) than either is to humans.
The two lineages leading to modern humans and [chimps+ bonobos] separated about 8 million years ago. Chimpanzees [Pan troglodytes] and Bonobos [Pan paniscus] have some genetic divergence, which is estimated [Wikipedia] to have emerged at about a million or so years ago. So in broad terms they are ~eight time closer to each other than humans are to either.
Smithsonian has a very good discussion on the current science, although skewed strongly to the human side - http://humanorigins.si.edu/evidence/genetics.
The Timetree website is an interesting way to play with questions like this. Plugging in the different pairs of species, you find that the divergence time between chimpanzees and bonobos is the lowest (Median Time: 2.375 MYA [million years ago], Estimated Time: 2.820 MYA), and that the divergence time between Homo sapiens and either of the two Pan species is the same (Median Time: 6.40 MYA, Estimated Time: 6.65 MYA).
Comparisons of gorillas on the one hand, and humans or either of the two Pan species on the other, all give the same value: Median Time: 8.61 MYA, Estimated Time: 9.06 MYA.
Any of the African great apes (us, chimpanzees and bonobos, and gorillas) compared with the orangutans gives the same result: Median Time: 15.20 MYA, Estimated Time: 15.76 MYA.
Any of the great apes (us, chimpanzees and bonobos, gorillas, and orangutans) compared with the gibbons gives the same result: Median Time: 19.43 MYA, Estimated Time: 20.19 MYA.
This Quora answer has a nice “cladogram” showing the relationship between humans, chimpanzees and bonobos, gorillas, orangutans, and gibbons.
This might be a little more informative.
Basically we split from the common ancestor for both humans, chimps and bonobos some 5-6 million years ago, and they split from their own common ancestor a million and half years ago.
“What’s the closest species?” usually depends on what you consider a different species. If, for instance, you maintain (contrary to the current consensus) that the Pan apes on both sides of the Congo are the same species, then that species’ closest relative is indeed human.
Where it gets really weird is that, by some standards, the species most closely related to humans diverged from us 68 years (plus a week) ago.
That’s a hela stretch.
I’m guessing I’m not quite up on my comic/sci-fi lore enough to realize what happened in February 1951…
Not comics or sci-fi; real life. As Ludovic punningly referred to, HeLa cells were first cultured in February 1951. And, yes, it seems a stretch to call them a new species… but it seems even more of a stretch to not call them a new species. Sometimes, biology is just weird, and defies our attempts at classification.
To add to MEBuckner’s comments, in case it’s not clear - the times are identical in each case because they refer to a single node on the tree of life. The topology of the tree is known in most cases with absolute certainty, although the times have a margin of error. In the first case, the node is the speciation event when the common ancestor of [gorilla, chimp, human] split into two lineages: the ancestor of gorilla and the common ancestor of [chimp, human]. So the divergence time between human and gorilla is exactly the same as the divergence time between any chimp and gorilla.
By way of analogy, if my aunt has two children, I can’t meaningfully ask to which of them I’m more closely related, because they’re both my cousins. But they’re both more closely related to each other than either is to me.
In the analogy, humans and Pan would be siblings, with gorillas a cousin to both.
To further extend that analogy: Humans are an “only child” species; we don’t have any siblings (or at least none that lived). Chimpanzees and bonobos are “sister species” (the two “daughter species” of Aunt Pan, sister to Mama Homo) and are thus both equally “first cousins” to humans. Gorillas (there are actually a couple of sibling species in Genus Gorilla) are like the grandchildren of your grandmother’s sister: They’re equally “second cousins” to both us Homo sapiens and to the Pan kids, Chimpanzee and Bonobo.
Well, *some *of our siblings live on in us - like a clump of cells from a reabsorbed twin, the Neanderthals and Denisovans lives on in us.
One of my siblings was quite incensed when 23 and Me informed her that she shared 50% of her DNA with me but 98% with chimpanzees 
It shoudl be noted that both species of Chimps were considered one until fairly recently.
That was my first thought (that the factoid predated the taxonomic split into two species) too, but googling showed that the split wasn’t that recent, decades before DNA hybridization was first used to estimate relatedness.
When I was in school a bonobo was a TYPE of chimpanzee.
They have since been reclassified.
Aha. I’d read of these before at SDMB, but even if I’d remembered them, I wouldn’t have remembered the date or made a connection.
I did check Wikipedia’s pages for both 1951 and various February dates hoping to solve the puzzle, but saw no mention of HeLa. (A woman had a cyst weighing hundreds of pounds ( :eek: ) removed about that date — I wondered if that was part of the puzzle!)
My brother in law married a bonobo. I know we’re not technically related, but it’s still awkward at the holidays.