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Category Archives: primate evolution

Ancient Italian ape had human-like precission grip

Reconstruction of O. bamboli (Pavel Major / ICP)
Oreopithecus bamboli was primate species, surely a hominine (great ape excluding orangutans) that lived in Tuscany and Sardinia some 8.2-6.7 million years ago.
It has great interest regarding human evolution because it is the oldest known ape to have developed a pad-to-pad precision grip, a characteristic otherwise only found in the human genus.
This trait, hotly debated in the last decades, has been recently confirmed by researchers of the Catalan Institute of Paleontology Miquel Crusafont (ICP). It must be said however that this development is considered convergent evolution and not ancestral to our own precision grip.
O. bamboli fossil
(CC by Ghedoghedo)
I guess that much of the controversy is caused by the old hypothesis that argued that it was the precision grip itself which elicited human brain development, something that obviously did not happen with Oreopithecus.
Other traits of this species are quite different from our own or our australopithecine relatives. They probably walked upright but with different gait (unlike the more human-like Sahelanthropus, of similar age) and their feet were very much unlike ours, with a very open angle for the big toe (hallux).
It seems that their environment was swampy and not strictly forestal.
Sources[es/cat/en]: Pileta, Diari de Girona, Wikipedia.
Ref.: Sergio Almécija et al., The morphology of Oreopithecus bambolii pollical distal phalanx. AJPA 2014. Pay per viewLINK [doi:10.1002/ajpa.22458]
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55 million years old evolved primate fossil

A small early Tarsiiforme specimen, named Archicebus achilles, lived some 55 million years ago in what is now Central China, it has been known from a recently discovered fossil (right).
This primate was already an ancestor of modern tarsiers, then just diverged from the line leading to us Anthropoidea, what comes to support the theories that suggest an old origin of the primate lineage, possibly c. 85 Ma ago, still in the Cretaceous era, when T. rex and all the famous Hollywood dinosaurs still roamed the Earth.
And this has of course implications as well for the origin of mammals, popularly believed to be in a very early stage of their evolution in that period… but maybe much more diversified than some pop documentaries want us believe. 
Until now the oldest known primate was Plesiadapsis, a proto-lemur that may look maybe more like a squirrel than a primate (at least to my eyes). Plesiadapsis is from the same time as Achicebus, c. 55-58 Ma ago. 

Primate phylogenetic tree (from Wikipedia) with the aprox. placement of Archicebus

Ref. X. Ni et al. The oldest known primate skeleton and early haplorhine
evolution. Nature. Vol. 498, June 6, 2013, p. 60.
doi:10.1038/nature12200.
 
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Posted by on June 10, 2013 in primate evolution

 

Neanderthals weaned their babies between 9 and 18 months of age

Or at least one of them did. 
The finding is the product of detailed analysis of milk tooth formation in one infant Neanderthal from Scladina cave (Belgium) and comparison with many monkey teeth. The researchers concluded that the barium accumulation in the teeth correlates tightly with breastfeeding and gives information on this with almost a day of precision.
This Neanderthal kid was exclusive breastfed up to the age of nine months and then had another nine months of gradual weaning, eating also other foods, as well as its mother’s milk. 
This is probably much more than the average breastfeeding in our modern societies but less than it has been documented among some hunter-gatherers like Bushmen, who may well partly breastfeed their children for up to four years, what acts as (unsafe) contraceptive. Chimpanzees seem to breastfeed their infants for some 5.3 years, while non-civilized humans (H. sapiens) have ranges of around 2.4 years instead.
Sources: Science Daily, Paleorama[es].
Ref. Christine Austin, Tanya M. Smith, Asa Bradman, Katie Hinde, Renaud
Joannes-Boyau, David Bishop, Dominic J. Hare, Philip Doble, Brenda
Eskenazi, Manish Arora. Barium distributions in teeth reveal early-life dietary transitions in primates. Nature, 2013; DOI: 10.1038/nature12169
 

Is it music what makes us humans?

Alright, the title is a blunt cliché admittedly. But that is what a new study on rhesus monkeys has found: that our intelligent cousins from India cannot discern the beat, the regularity that makes up a rhythm. Human babies can instead and so is the case of some birds.

Henkjang Honing et al., Rhesus Monkeys (Macaca mulatta) Detect Rhythmic Groups in Music, but Not the Beat. PLoS ONE 2012. Open accessLINK [doi:10.1371/journal.pone.0051369]

Abstract


It was recently shown that rhythmic entrainment, long considered a
human-specific mechanism, can be demonstrated in a selected group of
bird species, and, somewhat surprisingly, not in more closely related
species such as nonhuman primates. This observation supports the vocal learning hypothesis
that suggests rhythmic entrainment to be a by-product of the vocal
learning mechanisms that are shared by several bird and mammal species,
including humans, but that are only weakly developed, or missing
entirely, in nonhuman primates.
To test this hypothesis we measured
auditory event-related potentials (ERPs) in two rhesus monkeys (Macaca mulatta),
probing a well-documented component in humans, the mismatch negativity
(MMN) to study rhythmic expectation. We demonstrate for the first time
in rhesus monkeys that, in response to infrequent deviants in pitch that
were presented in a continuous sound stream using an oddball paradigm, a
comparable ERP component can be detected with negative deflections in
early latencies (Experiment 1). Subsequently we tested whether rhesus
monkeys can detect gaps (omissions at random positions in the sound
stream; Experiment 2) and, using more complex stimuli, also the beat
(omissions at the first position of a musical unit, i.e. the ‘downbeat’;
Experiment 3). In contrast to what has been shown in human adults and
newborns (using identical stimuli and experimental paradigm), the
results suggest that rhesus monkeys are not able to detect the beat in
music. These findings are in support of the hypothesis that beat induction
(the cognitive mechanism that supports the perception of a regular
pulse from a varying rhythm) is species-specific and absent in nonhuman
primates. In addition, the findings support the auditory timing dissociation hypothesis,
with rhesus monkeys being sensitive to rhythmic grouping (detecting the
start of a rhythmic group), but not to the induced beat (detecting a
regularity from a varying rhythm).

Sadly for the enthusiasts of “complex modern behavior”, who’d love to draw an absolutist line between before and after of being humans, music leaves no or almost no remains, so their line, even if it might exist in blurry or whatever other state, cannot be identified in the archaeological record.
 
 

Blood groups A and B inherited from simian ancestors

A new study has found that blood group A and B alleles have been stable (albeit in likely dynamic equilibrium) in the primate family since… always.

Laure Ségurel et al., The ABO blood group is a trans-species polymorphism in primates. PNAS 2012. Pay per view (6 months embargo) ··> LINK [doi:]

Abstract

The ABO histo-blood group, the critical determinant of transfusion incompatibility, was the first genetic polymorphism discovered in humans. Remarkably, ABO antigens are also polymorphic in many other primates, with the same two amino acid changes responsible for A and B specificity in all species sequenced to date. Whether this recurrence of A and B antigens is the result of an ancient polymorphism maintained across species or due to numerous, more recent instances of convergent evolution has been debated for decades, with a current consensus in support of convergent evolution. We show instead that genetic variation data in humans and gibbons as well as in Old World monkeys are inconsistent with a model of convergent evolution and support the hypothesis of an ancient, multiallelic polymorphism of which some alleles are shared by descent among species. These results demonstrate that the A and B blood groups result from a trans-species polymorphism among distantly related species and has remained under balancing selection for tens of millions of years—to date, the only such example in hominoids and Old World monkeys outside of the major histocompatibility complex.

Razib has some more details on the matter (being PPV, I haven’t read it). Still he wonders what kind of disease or otherwise evolutionary pressure may have been so virulent as to keep the whole order of primates (or at the very least all simians) on our toes all these millions of years.
The answer may well be known already: it seems that type A blood protects against the plague, while type B protects against smallpox, both great historical killers of those without enough defenses. However they may favor other less important health problems like blood clots or cancer, enough to exert a mild pressure in favor of a return to the basic type zero (“O”), which would have evolved by loss of function once and again. 
Whatever the case I find fascinating that these immune mechanisms may be so extremely persistent and I wonder if the bacterian mechanisms they confront may be more generic than just an specific disease.
See also: maps of distribution of major blood types.

Update: a pre-print copy of the paper is available at arXiv.

 
 

Chimps and humans diverged some eight million years ago

I have said that several times. So I’m not going to miss the opportunity of saying it once more: the 5 million year figure for the Pan-Homo divergence is a total nonsense: it’s more like 8-10 million years. Even the less exaggerated hunch (not sure on what is based) of 7 million years is too short.
New research, using mathematical-statistic analysis with not one but several cross-references, produces an older figure: some 8 million years.

Abstract

Estimation of divergence times is usually done using either the fossil record or sequence data from modern species. We provide an integrated analysis of palaeontological and molecular data to give estimates of primate divergence times that utilize both sources of information. The number of preserved primate species discovered in the fossil record, along with their geological age distribution, is combined with the number of extant primate species to provide initial estimates of the primate and anthropoid divergence times. This is done by using a stochastic forwards-modeling approach where speciation and fossil preservation and discovery are simulated forward in time. We use the posterior distribution from the fossil analysis as a prior distribution on node ages in a molecular analysis. Sequence data from two genomic regions (CFTR on human chromosome 7 and the CYP7A1 region on chromosome 8) from 15 primate species are used with the birth–death model implemented in mcmctree in PAML to infer the posterior distribution of the ages of 14 nodes in the primate tree. We find that these age estimates are older than previously reported dates for all but one of these nodes. To perform the inference, a new approximate Bayesian computation (ABC) algorithm is introduced, where the structure of the model can be exploited in an ABC-within-Gibbs algorithm to provide a more efficient analysis. 

Press article at Science Daily.
A central issue is that fossils are seldom preserved and discovered, so fossil evidence can well be five or 5.5 million years old and the divergence be in fact older.
But combining fossil and genetic data it is possible to refine the equation and get to much more accurate estimates. That’s what the authors have done in what should be celebrated as a the convergence of genetics and archaeology (paleontology in this particular case), a convergence much needed indeed. 

Toumaï
One of the particular fossils which find new room into the potential Human ancestry is Sahelanthropus tchadensis, Toumaï, which fits well in the evolutionary line of Homo sp. but was earlier thought by many as too old for that.
Another aspect vindicated by this study is that primates lived in the late era of the dinosaurs, what really allows them to have reached South America without need of swimming across an ocean which did not actually exist yet. 
This was actually addressed by the same team in 2002 but its obvious implications in human evolution were ignored. So they have now decided to address the matter themselves, what is very much appreciated, because they must be damn right.

Related posts (also from my old blog Leherensuge):