If you could back in time, how far back could you go while still retaining the ability to reproduce with a human of that era?
November 18, 2007 11:57 PM Subscribe
If you could back in time, how far back could you go while still retaining the ability to reproduce with a human of that era?
This post was deleted for the following reason: Hypothetical science-fiction chatfilter. -- cortex
Hypothetical-filter?
posted by allkindsoftime at 12:32 AM on November 19, 2007
posted by allkindsoftime at 12:32 AM on November 19, 2007
No assumptions about it, we can only reproduce with members of our own species; interbreedability is the definition of a species.
Based on that, LobsterMitten is right on the money.
posted by daniel striped tiger at 12:37 AM on November 19, 2007
Based on that, LobsterMitten is right on the money.
posted by daniel striped tiger at 12:37 AM on November 19, 2007
It depends on whether you require the children to be fertile, or are willing to accept "mules". A modern human might be able to breed with a hominid from even earlier than that, and produce offspring, without those offspring themselves being able to reproduce.
In other words, if you relax the standard so that you can produce children but no grandchildren, you could probably manage to go back half a million year.
posted by Steven C. Den Beste at 12:43 AM on November 19, 2007
In other words, if you relax the standard so that you can produce children but no grandchildren, you could probably manage to go back half a million year.
posted by Steven C. Den Beste at 12:43 AM on November 19, 2007
The difference between behaviorally modern and anatomically modern humans also confounds this question. For a great popular review of human evolution and prehistory, see Before the Dawn by Nicholas Wade.
Also, the definition of a species is not necessarily that easy. "Capable of interbreeding" doesn't specify genetically or behaviorally, and I'm not even touching species definition for organisms without sexual reproduction.
posted by agentofselection at 1:08 AM on November 19, 2007
Also, the definition of a species is not necessarily that easy. "Capable of interbreeding" doesn't specify genetically or behaviorally, and I'm not even touching species definition for organisms without sexual reproduction.
posted by agentofselection at 1:08 AM on November 19, 2007
interbreedability is the definition of a species.
Not always true, Bottle Nose Dolphins and False Killer Whales can interbreed and produce viable offspring, and they are still considered different species.
We don't really know how far you can go back and still have viable offspring. It now seems that modern humans did not reproduce with Neandertals, but we don't know why.
posted by afu at 1:17 AM on November 19, 2007
Not always true, Bottle Nose Dolphins and False Killer Whales can interbreed and produce viable offspring, and they are still considered different species.
We don't really know how far you can go back and still have viable offspring. It now seems that modern humans did not reproduce with Neandertals, but we don't know why.
posted by afu at 1:17 AM on November 19, 2007
It's a statistical question. Right now there a certain percentage of humans of the opposite sex with whom you are fertile, and it is definitely not 100%. If you went further back in time, this number would decrease. At some point, it would attenuate to a tiny number of individuals, but I suspect you wouldn't recognize them as humans. They'd look a lot more like the common ancestor of us and other primates, than we do.
We might be interfertile with Australopithecus afarensis; if so, that puts the date for the date around -4 million years +/- 25%.
posted by aeschenkarnos at 3:59 AM on November 19, 2007
We might be interfertile with Australopithecus afarensis; if so, that puts the date for the date around -4 million years +/- 25%.
posted by aeschenkarnos at 3:59 AM on November 19, 2007
Artist's renditions of Australopithecus afarensis here here if you want to check out the hotties in question.
posted by aeschenkarnos at 4:01 AM on November 19, 2007
posted by aeschenkarnos at 4:01 AM on November 19, 2007
i seem to recall that human and neanderthal interbreeding was not only possible but actually happened, but i can't recall the source. it was not "clan of the cave bear."
posted by thinkingwoman at 4:09 AM on November 19, 2007
posted by thinkingwoman at 4:09 AM on November 19, 2007
Daniel: If you line up every animal in your lineage, starting with you, your parents, your grandparents, right the way back to, say, the earliest placental mammals, then every animal in that chain will be capable of mating with both the generation before it, and the generation after it. Probably hundreds of generations either side, in fact. So are they all members of a single species? IMO that definition isn't terribly useful when you get beyond extant species. You end up with something like a ring species but smeared across time rather than geography.
(The original question is probably unanswerable, so I'm just going to speculate here. If we start by looking for pairs of mammal species that can interbreed (eg lion+tiger, bottlenose dolphin+false killer whale, horse+donkey), and rank them by (a) how often they produce offspring (b) how often those offspring are fertile and (c) how long ago their common ancestor lived, we might find some kind of relationship. We can then assume that if the living species can interbreed, they would both be able to breed successfully at least as far back as their common ancestor, and probably much further. That might give you some kind of lower bound.
What you're really looking for is a statement along the lines of "every pair of mammal species that diverged less than x million years ago can interbreed with a success rate of at least Y%".
The upper bound can't be found because although there are plenty of pairs that can't interbreed (human+chimpanzee), it's still possible that (human+common ancestor) and (chimpanzee+common ancestor) are somewhat-viable pairings).
posted by Leon at 4:16 AM on November 19, 2007
(The original question is probably unanswerable, so I'm just going to speculate here. If we start by looking for pairs of mammal species that can interbreed (eg lion+tiger, bottlenose dolphin+false killer whale, horse+donkey), and rank them by (a) how often they produce offspring (b) how often those offspring are fertile and (c) how long ago their common ancestor lived, we might find some kind of relationship. We can then assume that if the living species can interbreed, they would both be able to breed successfully at least as far back as their common ancestor, and probably much further. That might give you some kind of lower bound.
What you're really looking for is a statement along the lines of "every pair of mammal species that diverged less than x million years ago can interbreed with a success rate of at least Y%".
The upper bound can't be found because although there are plenty of pairs that can't interbreed (human+chimpanzee), it's still possible that (human+common ancestor) and (chimpanzee+common ancestor) are somewhat-viable pairings).
posted by Leon at 4:16 AM on November 19, 2007
No assumptions about it, we can only reproduce with members of our own species; interbreedability is the definition of a species.
Interbreedability is part of the biological species concept. When dealing with extinct populations, however, that concept is worthless, because bones just can't mate. Those extinct populations are grouped into species by morphological characteristics and, to a lesser extent and only for more recent samples, genetics. In Paleoanthropology, the former is something of a dark art, with early paleoanthropologists essentially making judgment calls as to what looked more or less like other things. "This one has big teeth? New species!" The uncertainty surrounding it has played to two general camps of Paleoanthropologists, the lumpers and splitters, who tend to minimize or maximize the differences between populations respectively. The former, for example, may say that based on morphology, anatomical ancient modern humans and Neandertals are the same species. The latter camp would assert that they're very different species. All of this is exacerbated by the fact that a new species makes one very very famous around the Paleoanthropological community, and even the wider world of the science-minded (think National Geographic covers, NY Times articles), and that is very lucrative to underpaid academics. Modern morphometric study of the bones is still in its infancy, and is starting to shed some more, shall I say, scientific light on the morphological differences between ancient populations (Katarina Harvati and Tim Weaver are two people doing great work on this in the last few years). Harvati in particular has noted that the quantified morphological distinctions between Neandertals and modern humans are greater than subspecific differences between other catarrhines (Old World monkeys and apes). Based on this, her and her co-authors' opinion is a species-level distinction between Neandertals and modern humans (Harvati et al 2004, PNAS 101: 1147-1152).
Genetic study is still relatively very new, with the first ancient DNA processes developed circa 1989 and the first non-anatomically modern human DNA (Neandertals) being published in 1997 (Krings et al 1997, Cell 90: 19-30). Up until the last year, a handful of Neandertal DNA was analyzed, but only mitochondrial DNA, as nuclear DNA was considered too poorly degraded to be analyzed. In the last year, however, the same lab as published the Krings paper (the lab belonging to Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig; these are the people that brought you the Neandertals-had-red-hair news that swept the science sections of your local paper a few weeks ago) has developed methods for sequencing badly-degraded ancient nuclear DNA, and have begun publishing those data, including a 1,000,000-base-pair set of the nuclear DNA (Green et al 2006, Nature 444: 330-336) and, earlier this month, the discovery of a modern version of FOXP2 in Neandertals (Krause et al 2007, Current Biology 17(21): 1908-1912), a gene thought to be necessary for modern language (that doesn't mean Neandertals DID have language, but that they weren't prevented from speaking by lack of the gene). What the body of genetic evidence from 1997 to now is telling us re: Neandertals and modern humans is that they are certainly distinct populations, and there is no evidence for interbreeding.
Now, a few Paleoanthropologists do claim to have found evidence for interbreeding in the form of hybrid children (always children...). The most notable recently has been the one from Lagar Velho 1, Portugal (citations in the link). The finders (Trinkaus and Zilhao) described it as a hybrid between a Neandertal and a modern human, while Tattersall and Schwartz responded that it looked like a robust human child. It very well may be a hybrid, but a child skeleton is poor evidence of hybridization because 1) there's no idea of its viability (ability to breed itself and create new offspring), 2) the morphology of children is very variable and different than that of adults, and 3) the sample of Neandertal children is incredibly low for comparison. Due to these and other uncertainties, the issue of whether or not this skeleton is actually a hybrid is far from resolved (and this applies to the handful of other "hybrid" children discovered), and moreover, even if it were, the fact that we don't know if the child was viable still prevents us from addressing the biological species concept question.
So where does this leave us? The specific designations vis-a-vis Neandertals and modern humans are still unclear, even to specialists. There is overwhelming support in the scientific community that Neandertals were a separate species, or at least a separate population, though there are a few hangers-on to the idea of one large interbreeding population. The bones (in modern quantifiable study) indicate that Neandertals were distinct from modern humans at the species level. The genetic evidence indicates that they were distinct, maybe at the species level, maybe at the subspecies level. There probably wasn't regular interbreeding between the two groups, but there may have been instances of interbreeding between them. Prior to Neandertals, all bets are off regarding interbreeding, as there are no genetic data from which to draw conclusions and the skeletal data are still somewhat ambiguous.
More to the point of the question the OP posed, if you or I were to go back in time, we certainly could have mated with an ancient modern human from up to around 24,000 years ago. The humans then are genetically and morphologically indistinct from modern populations (Caramelli et al 2004, PNAS 100: 6593-6597). Prior to that, if there is genetic continuity between the Omo specimens cited in an above comment and modern populations, yeah, we probably could have mated with the earliest modern humans at ~200 kya. Could we mate with Neandertals? Maybe. My general sense is that it was possible, but really we have no way to know. Prior species like Homo heidelbergensis or Homo ergaster? No idea, and I couldn't even speculate.
posted by The Michael The at 5:59 AM on November 19, 2007 [4 favorites]
Interbreedability is part of the biological species concept. When dealing with extinct populations, however, that concept is worthless, because bones just can't mate. Those extinct populations are grouped into species by morphological characteristics and, to a lesser extent and only for more recent samples, genetics. In Paleoanthropology, the former is something of a dark art, with early paleoanthropologists essentially making judgment calls as to what looked more or less like other things. "This one has big teeth? New species!" The uncertainty surrounding it has played to two general camps of Paleoanthropologists, the lumpers and splitters, who tend to minimize or maximize the differences between populations respectively. The former, for example, may say that based on morphology, anatomical ancient modern humans and Neandertals are the same species. The latter camp would assert that they're very different species. All of this is exacerbated by the fact that a new species makes one very very famous around the Paleoanthropological community, and even the wider world of the science-minded (think National Geographic covers, NY Times articles), and that is very lucrative to underpaid academics. Modern morphometric study of the bones is still in its infancy, and is starting to shed some more, shall I say, scientific light on the morphological differences between ancient populations (Katarina Harvati and Tim Weaver are two people doing great work on this in the last few years). Harvati in particular has noted that the quantified morphological distinctions between Neandertals and modern humans are greater than subspecific differences between other catarrhines (Old World monkeys and apes). Based on this, her and her co-authors' opinion is a species-level distinction between Neandertals and modern humans (Harvati et al 2004, PNAS 101: 1147-1152).
Genetic study is still relatively very new, with the first ancient DNA processes developed circa 1989 and the first non-anatomically modern human DNA (Neandertals) being published in 1997 (Krings et al 1997, Cell 90: 19-30). Up until the last year, a handful of Neandertal DNA was analyzed, but only mitochondrial DNA, as nuclear DNA was considered too poorly degraded to be analyzed. In the last year, however, the same lab as published the Krings paper (the lab belonging to Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig; these are the people that brought you the Neandertals-had-red-hair news that swept the science sections of your local paper a few weeks ago) has developed methods for sequencing badly-degraded ancient nuclear DNA, and have begun publishing those data, including a 1,000,000-base-pair set of the nuclear DNA (Green et al 2006, Nature 444: 330-336) and, earlier this month, the discovery of a modern version of FOXP2 in Neandertals (Krause et al 2007, Current Biology 17(21): 1908-1912), a gene thought to be necessary for modern language (that doesn't mean Neandertals DID have language, but that they weren't prevented from speaking by lack of the gene). What the body of genetic evidence from 1997 to now is telling us re: Neandertals and modern humans is that they are certainly distinct populations, and there is no evidence for interbreeding.
Now, a few Paleoanthropologists do claim to have found evidence for interbreeding in the form of hybrid children (always children...). The most notable recently has been the one from Lagar Velho 1, Portugal (citations in the link). The finders (Trinkaus and Zilhao) described it as a hybrid between a Neandertal and a modern human, while Tattersall and Schwartz responded that it looked like a robust human child. It very well may be a hybrid, but a child skeleton is poor evidence of hybridization because 1) there's no idea of its viability (ability to breed itself and create new offspring), 2) the morphology of children is very variable and different than that of adults, and 3) the sample of Neandertal children is incredibly low for comparison. Due to these and other uncertainties, the issue of whether or not this skeleton is actually a hybrid is far from resolved (and this applies to the handful of other "hybrid" children discovered), and moreover, even if it were, the fact that we don't know if the child was viable still prevents us from addressing the biological species concept question.
So where does this leave us? The specific designations vis-a-vis Neandertals and modern humans are still unclear, even to specialists. There is overwhelming support in the scientific community that Neandertals were a separate species, or at least a separate population, though there are a few hangers-on to the idea of one large interbreeding population. The bones (in modern quantifiable study) indicate that Neandertals were distinct from modern humans at the species level. The genetic evidence indicates that they were distinct, maybe at the species level, maybe at the subspecies level. There probably wasn't regular interbreeding between the two groups, but there may have been instances of interbreeding between them. Prior to Neandertals, all bets are off regarding interbreeding, as there are no genetic data from which to draw conclusions and the skeletal data are still somewhat ambiguous.
More to the point of the question the OP posed, if you or I were to go back in time, we certainly could have mated with an ancient modern human from up to around 24,000 years ago. The humans then are genetically and morphologically indistinct from modern populations (Caramelli et al 2004, PNAS 100: 6593-6597). Prior to that, if there is genetic continuity between the Omo specimens cited in an above comment and modern populations, yeah, we probably could have mated with the earliest modern humans at ~200 kya. Could we mate with Neandertals? Maybe. My general sense is that it was possible, but really we have no way to know. Prior species like Homo heidelbergensis or Homo ergaster? No idea, and I couldn't even speculate.
posted by The Michael The at 5:59 AM on November 19, 2007 [4 favorites]
If you have built a time machine, take condoms with you.
posted by Cat Pie Hurts at 6:38 AM on November 19, 2007
posted by Cat Pie Hurts at 6:38 AM on November 19, 2007
Hypothetical-filter?
Shush. Do you want the mods to delete awesome questions like this?
posted by John Kenneth Fisher at 6:56 AM on November 19, 2007
Shush. Do you want the mods to delete awesome questions like this?
posted by John Kenneth Fisher at 6:56 AM on November 19, 2007
This thread is closed to new comments.
Could we reproduce with Neanderthals or other early proto-humans? I don't know.
posted by LobsterMitten at 12:12 AM on November 19, 2007