Creationists and other critics of evolution have long derided the notion that humans “descended from monkeys.” Of course, this isn’t what scientists claim — scientists only assert that human and monkeys (and other modern-day primates) descended from some common ancestors through a chain of intermediate species. But even when conceding this point, creationists still insist that the “missing links” between human and primate don’t exist.
But scientists point out that many hominin species have been identified (hominins are fossils representing extinct species in that may have been ancestral to humans). For instance, Ian Tattersall has sketched 22 hominin species in a “family tree” graphic available at Prehuman fossils and also in [Prothero2007]. And even Tattersall’s illustration is out of date — it does not include several species, such as Ardipithecus ramidus and Australopithecus sediba, which have only been uncovered in the past year or two.
In yet another remarkable discovery, in March 2010 a team led by two researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig announced discovery of a new hominin species, identified as the result of analyzing mitochondrial DNA (mtDNA) found in a finger and tooth found in Siberia. This species co-existed with humans until as recently as 50,000 years ago, yet is roughly twice as distant (measured in terms of the time since a common ancestor) from modern humans as Neanderthals. As explained in a Scientific American report [Wong2010a],
Comparing the order of the genetic “letters” — or base-pairs, as they are termed — making up the Denisova [Siberian] mtDNA with the sequences of modern day humans and an early modern human, Krause and his collaborators found that the Denisova mtDNA differed from humans today in nearly twice as many letter positions as Neanderthal mtDNAs do.
A follow-up study published in December 2010, based on an entire genome sequence of the specimen, found that not only do the Denisovans represent a “sister” species to Neanderthals, but that in fact this race of prehumans evidently interbred with Southeast Asian humans, since the genomes of modern-day New Guinea natives contain 4.8% Denisovan DNA [Zimmer2010a].
Numerous other details of this discovery are available in an interesting article by biologist Carl Zimmer, published in December 2010 in the New York Times [Zimmer2010a].
In summary, there is no truth to the claim by creationists and others that there are no “missing links” between ancient apes and humans. If anything, there is an embarrassment of riches — so many specimens have been found in the past decade or two that the only challenge is clearly establishing their positions in the “family tree” and deciding which are truly in the direct line that leads to modern humans and which are evolutionary dead ends.
If anything, we should celebrate, not resist, these findings, since they underscore how singular and successful our species has been. What were the factors that led to our survival and ultimate dominance? These are active areas of research, and we can look forward to enlightening results in the future.
Additional discussion of prehuman fossils is available at Prehuman fossils and in Prothero’s book [Prothero2007].
References
- [Prothero2007] Donald R. Prothero, Evolution: What the Fossils Say and Why It Matters, Columbia University Press, New York, 2007.
- [Wong2010a] Kate Wong, “No Bones about It: Ancient DNA from Siberia Hints at Previously Unknown Human Relative,” Scientific American, 24 Mar 2010, available at Online article.
- [Zimmer2010a] Carl Zimmer, “Siberian Fossils Were Neanderthals’ Eastern Cousins, DNA Reveals,” New York Times, 22 Dec 2010, available at Online article.