Humans and chimpanzees share 99.4% of their DNA, making chimps our closest relatives. (This is, at least, Conventional Wisdom. If it’s wrong, let me know).
I started wondering what our relationship is to other animals out there.
How closely are we related to dogs and cats? Do we share more DNA with one or the other, or are they similarily distinct from us on a genetic level?
Are cats and dogs more closely related to each other than they are to humans?
And what about other domesticized animals? Which are we most closely related to? Horses? Cows? Lab rats? Swine?
Finally, what’s our closest non-primate species relative? Non-mammal?
The short answer to your question, though, is that cats and dogs have a common ancestor 65 or so million years ago. You’d have to go back considerably further to find a common ancestor with humans. One thing I read is that possibly our closest living relatives (other than the primates) might be rodents and lagomorphs or other insectivores. Don’t know how widely accepted that is, though.
Here’s the way to think about your question. If we were more closely related to, say, dogs than we are to cats, that would mean that dogs would have to be more closely related to humans than they would be to cats. But we know that dogs and cats are both members of the order Carnivora, while humans are members of the order Primates. Cats and dogs share a common ancestor from around the time of the extinction of the dinosaurs. But our common ancestor with that ancestral carnivore was much earlier.
We are most closely related to chimpanzees. And chimps are more closely related to humans than they are to gorillas. Chimps, humans, and gorillas are more closely related to each other than they are to orangutans. All apes are more closely related to each other than they are to any monkey. Apes and old-world monkeys are more closely related to each other than they are to new-world monkeys.
Any animal outside of a clade is equally related to any animals inside the clade. Think of a branching tree. Lets say a tree with two branches, and two twigs on each branch. A species is most closely related to the twig on the same branch. But it is equally distant to the two twigs on the other branch, neither is more closely related, no matter how similar they look.
So we can say that primates are probably more similar to rodents than we are to artiodactyls, but we can also say that no primate is more similar to any rodent than any other primate, and no rodent is more similar to any primate than any other rodent. Every rodent is equally related to every primate, and every primate is equally related to every rodent. So although there are groups that are more similar to primates than other groups, there is no SPECIES which is more similar to primates than any other species. So there is no non-primate species which is phylogenetically more closely related to humans than any other.
Nitpick: This could technically be incorrect if there was an order than contained only one species, such as Tubulidentata which contains only the aardvark. So the aardvark could concievably be the closest relative of, say, every artiodactyl (I don’t know where it is placed right now). But that is only because every other Tubulidentate is extinct. http://www.ultimateungulate.com/tubulidentata.html
Could you elucidate? I’ve read that it’s believed (however unlikely) that the ancestors of New World monkeys arrived from Africa by sea while South America and Africa were much closer. Wouldn’t the “monkey line” have already diverged from the “ape line?” Is there a more plausible competing theory on the arrival of New World monkeys?
This answers the crux of my question, really. But it prompts another one: has this been proven through DNA similarity? In other words, will both dog and cat DNA match human DNA to the same percentage? For example, where chimps are 99.4% similar, dogs and cats are both 88.3% similar (or whatever – the number is hypothetical)?
And – you knew this was coming – what percentage of our DNA does overlap with dogs and cats?
Well, according to the tree in Earl’s link (and I have no previous familiarity with this source, or this particular tree, so I can’t vouch for how widly accepted it is), the closest non-primate to humans are the tree shrews (order Scandentia, which contains about 19 living species). Next closest are both Dermoptera (two species of “flying lemurs”) and the Chiroptera – i.e., the approximately 1000 species of bats, which I think is pretty cool.
One cannot infer from this tree which is the next closest related group beyond this – the polytomy (where all branches come from the same node) means that there is no evidence to support any claims deeper than this (i.e., that Insectovora are most closely related). There may, however, be other trees out there with more resolution at this node.
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I just did a cursory search, and didn’t find much in the way of alternate trees. Here’s one from a source I generally trust (although it’s usually a bit out of date), and it’s largely the same as Earl’s. So from this tree we see that, other than tree shrews, “flying lemurs,” and bats, we can’t say that humans are most closely related to any other non-primate placental mammals – except that Edentata and Pholidota are basal to all the rest.
A strict percentage number would be fairly hard to define and measure, and would likely be fairly meaningless if you did.
Do tell? Do you have a cite for that, perchance? Is the National Geographic tree online? (I didn’t see anything at first glance.) Do you have a cite from anything more scientific? (Not to disparage National Geographic, but is there anything in Science or Nature, etc.?) I thought that previous tree was based on molecular evidence.
While that’s probably true, it doesn’t preclude a closer relation ship between humans and old-world monkeys. Apes evolved from old-world monkeys after the new world monkeys had evacuated, not before. So our direct ancestors are old world monkeys, which in turn share a common ancestor with new world monkeys.
Excellent question and you proabably nailed the answer close enough for “government work”. (And yes, genetic data should show exactly the same genetic distance between man/dog and man/cat.)
I’ve never seen the genetic data for man/dog, but I have seen it for man/mouse, which is about 90%, IIRC. One would expect the man/dog and man/cat numbers to be just a hair less (no pun intended).
And, BTW, we can be shown to share something like 30% of our genetic material with plants. In fact, I’ve seen it stated that that the human/plant % similarity is so meaningless that it really should be considered the “zero point” of genetic similarity. Those genes that we do share probably are the ones that control cell function, growth, and splitting.
Also, the 99.4% number for chimp/human relatedness is not generally accepted throughout the scientific community. You’ll usually see something more like 98.5% or so. Check out this thread for some good discussion about the subject of genetic relatedness.
A more recent supertree (.pdf document, from 2001 - the one linked to by Earl is from 1999), constructed from a combination of genetic and morphological data, confirms what eburacum45 mentioned. We (primates) are still most closely related to family Tupaiidae (tree shrews), and bats have been moved to a much larger clade which includes cetaceans, artiodactyls, perissodactyls, and Carnivora. Based solely on morphology, we do seem to be closest to bats (see Fig 2B in the document). However, based on molecular data, we are closest to tree shrews and flying lemurs.
As Tamerlane’s cites show, they aren’t really lemurs. Then again, they don’t really fly, either. So these poor critters wind up saddled with a name that’s about as inappropriate (and confusing) as can be. Better just to call them colugos, I guess.
Wow, Darwin’s Finch, great tree! Thanks for the update. Although I must admit that I am disappointed that we are no longer thought to be so closely related to bats.
