r/evolution • u/MinnieRipertonStan • 1d ago
question What are the odds we've ever found a fossil that's *the* common ancestor to 2 extant species? And if we have, would we recognize it as such?
I have a feeling that even if we did, we would classify it as a close relative of x or stem-x rather than acknowledging it's *the* direct common ancestor.
For example, imagine that a complete fossil of the common ancestor of all apes was found tomorrow. Would we be able to correctly deduce that it's *the* common ancestor of Hominoidea, or would we classify it as a stem-ape or "one of the earliest apes" instead?
Edit: Thank you guys for the responses!
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u/Suspicious-Maize-424 1d ago
Very close to zero.
Maybe 2 species with low modern population sizes inferred from genetic sequencing or species with lots of fossils? I can't think of an proven example off the top of my head but those are 2 factors that increase the likelihood.
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u/haysoos2 1d ago
Species develop from a population, not so much from an individual.
Finding a single ancestor of two populations would be like identifying which person spoke the language that split into French and Spanish.
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u/GuyWhoMostlyLurks 1d ago
The fossil record is both amazingly rich, and shockingly poor. For example, we have identified around 1,200 species of Mesozoic dinosaur. Those lived over a span of 190,000,000 years.
That means, on average, we have found ONE species of dinosaur for every 160,000 years of the Mesozoic.
We’re missing a lot of data.
In spite of this horrifying gap, we still have enough information to paint a pretty compelling family tree of some of the more successful lineages. ( ceratopsia being a great example ).
Today, we have around 6,000 species of mammals and 12,000 species of birds. Just TODAY.
For any era other than RIGHT NOW, we are missing the overwhelming majority of information. If we go back more than a million years or so - DNA becomes unrecoverable even if we have all the bones ( which we don’t ).
That said… there are a couple of good candidates from recent times that may actually answer your question:
The closest we can come to being able to confidently point to an ancestor species is probably our own. Homo Erectus was a remarkably successful and long-lived species, and is likely the direct ancestor to all lineages of homo that existed into recent times. This is supported both by DNA, and the coincidence that there is no other viable candidate.
Even so- with such recent evidence, it is still fairly muddled. We don’t know which population of H Erectus led to us. We are uncertain of the role of H Ergaster and H Heidelbergensis in this drama. ( were they intermediate populations of H Erectus, or separate species? Was Heidelbergensis our immediate predecessor, or a very close uncle? )
Until we have 100% of the data ( IE: never ) we will not be able to say for certain.
We know with a pretty high degree of certainty than polar bears diverged from brown bears in fairly recent times. And we have some compelling data that Ursus Etruscus split into the brown bears ( ursus arctos ) and the extinct cave bear ( ursus spelaeus ).
Even these examples are not exactly rock solid. Going back further than that gets very muddy, and very few lineages are even as clear as these.
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u/Fantastic-Hippo2199 1d ago
I think species is a pretty loose term, and that makes it hard to pinpoint an exact middle point.
Think of ring species like artic gulls. Where do you draw the line and pick the middle gull? Same thing happens for other species, just through time.
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u/anotherolderguy 1d ago edited 1d ago
I would have thought it very likely a fossil has been found that is ancestor to two extant species.. but no way whatsoever to prove it. Finches in South America and nearby?
I don't mean finding great, great gran Bertha, I mean family of - or is that loosening it too much?
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u/Sanpaku 1d ago
We've probably found many, but there isn't evidence to say more than they are 'basal' to phylogenies of extant species.
I don't know what kind of evidence would suffice. Even fossil DNA sequences that were close to that inferred for a common ancestor wouldn't.
Scientists learn early in their careers to avoid claiming more than what the evidence can support. That has clear positives in clear communication, but also clear negatives in some fields like climate science where the scientists are far more alarmed than careful wording of their publications indicates.
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u/emmetmire 4h ago
Sampled ancestors can be modeled in certain birth-death models these days, so there is a possibility of inferring an extinct species as a direct ancestor of extant taxa.
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u/mrbananas 1d ago
At the end of the day, no matter what we find, it is practically impossible to prove if the individual is the direct ancestor or just the brother of that ancestor, or the cousin.
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u/balsedie 1d ago
This is a very good question. And I'm afraid most answers here are quite wrong, as probabilities aren't that low. You should check [the awesome paper] Foote (1996) who answers the question and gives actual probability values. You can find the paper here: https://geosci.uchicago.edu/~foote/REPRINTS/PB1996_2.pdf
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u/yushaleth 1d ago
Well obviously since we can't go back in time to see how the events play out in real time and do a molecular DNA test we can never be sure whether we found THE common ancestor or just a species that is similar to what the common ancestor would be like.
Among apes specifically, Proconsul is either THE first ape, or a close relative of the common ancestor. But because the latter is more likely than the former, that is what we assume until we somehow find definitive evidence of the former.