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Category Archives: biology

Poverty directly damages brain development

Children that at early ages have similar or even greater gray matter than their wealthier peers, get stuck in a weaker development as they grow just for being poor. That is what a new study has found:
Jamie L. Hanson et al., Family Poverty Affects the Rate of Human Infant Brain Growth. PLoS ONE 2013. Open access → LINK [doi:10.1371/journal.pone.0080954]

Abstract


Living in poverty places children at very high risk for problems across a variety of domains, including schooling, behavioral regulation, and health. Aspects of cognitive functioning, such as information processing, may underlie these kinds of problems. How might poverty affect the brain functions underlying these cognitive processes? Here, we address this question by observing and analyzing repeated measures of brain development of young children between five months and four years of age from economically diverse backgrounds (n = 77). In doing so, we have the opportunity to observe changes in brain growth as children begin to experience the effects of poverty. These children underwent MRI scanning, with subjects completing between 1 and 7 scans longitudinally. Two hundred and three MRI scans were divided into different tissue types using a novel image processing algorithm specifically designed to analyze brain data from young infants. Total gray, white, and cerebral (summation of total gray and white matter) volumes were examined along with volumes of the frontal, parietal, temporal, and occipital lobes. Infants from low-income families had lower volumes of gray matter, tissue critical for processing of information and execution of actions. These differences were found for both the frontal and parietal lobes. No differences were detected in white matter, temporal lobe volumes, or occipital lobe volumes. In addition, differences in brain growth were found to vary with socioeconomic status (SES), with children from lower-income households having slower trajectories of growth during infancy and early childhood. Volumetric differences were associated with the emergence of disruptive behavioral problems.

Figure 2. This figure shows total gray matter volume for group by age.

The data is clear (for details of the localized frontal and parietal evolution see figs. 3 and 4). The question is: why does this happen? The paper attempts also to discuss that:

These results extend a consistent literature in rodents, non-human
primates, and humans suggesting that early environments marked by stress
or deprivation negatively influence brain development [65][69].
This emerging body of research has found differences in brain structure
in portions of the frontal lobe, which fits well with the analysis
presented here [68].
These findings suggest that aspects of low SES environments have
important functional implications for children’s health and adaptation [70],
perhaps by influencing key features of central nervous system
development. In regards to neurobiological mechanisms, the differences
in volume we find are likely due to neuronal remodeling, rather than
birth of new neurons (or neurogenesis) [27], [71], [72].

(…)


Candidate factors might include the effects of household resources,
environmental stimulation, crowding, exposure to pathogens and noise,
parental stress, and nutrition. It is also possible that pre-natal
experiences affect brain development and reflect other disadvantages and
risks related to poverty. Because humans are able to adapt to a range
of environmental conditions, we must understand more about the level at
which impoverished environments become toxic for children.

And quite suggestively in the introduction they mention as well that:

Conditions such as the variety and complexity of the stimuli in an
animal’s cage can influence different aspects of brain structure,
including the number of neurons, glial cells, myelination, dendrites,
synapses, and neurogenesis (for review, see Ref. [23][24]). 

The specific causes can be many but I’d dare say that “caging”, i.e. the limitation of stimuli for living in smaller, impoverished, artificial habitats (including of course whatever limitations that the adults around them may have, such as low culture or emotional instability) is likely to be a key negative environmental factor for brain development.
On the other hand I can imagine that certain enrichment (cultural, health even technological, why not?) that has happened to our species in general in the last centuries, may be behind the so-called Flynn effect, which is that the measured IQ has been growing everywhere quite steadily. 
But in any case it is quite worrying that these social differences have such a big effect on the children and emphasizes the need to overcome them and to provide the best possible environment for the development of the future generations.
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Posted by on December 17, 2013 in biology, epigenetics, intelligence, mind, psychology, Sociology

 

Was the grove snail Epipaleolithic livestock in Western Europe?

Cepaea nemoralis
(CC by Papa Lima Whiskey 2)
The problem of disjunct distribution of Western European species or, in this case, subclades of a single species is nothing new and has been startling biologists for almost two centuries already, with particular interest of Irish-Iberian, Breton-Iberian or just general Irish-continental disjunct relationships of various species (the so called Lusitanian distribution). Among them is the iconic strawberry tree (madroño in Spanish, found in Ireland but not Great Britain) but also a number of small land animals: the Kerry slug (found in NW Iberia and SW Ireland only), the Quimper snail (found in NW Iberia and Western Brittany) or the Pyrenean glass snail (found in the Pyrenees and Ireland).
There are also cases of subclades within an otherwise widespread species which show a similar pattern. In 2003, Masheretti et al. demonstrated that the Irish variant of the pygmy shrew had its greatest affinity with populations of Andorra, in the Eastern Pyrenees, from which they are descended.
This study illustrates a similar case but affecting the snail species Cepaea nemoralis (grove snail or brown lipped snail), whose Irish lineages are mostly derived from Iberian ones and in most cases from the Eastern Pyrenean haplogroup C.
Adele J. Grindon & Angus Davison, Irish Cepaea nemoralis Land Snails Have a Cryptic Franco-Iberian Origin That Is Most Easily Explained by the Movements of Mesolithic Humans. PLoS Genetics 2013. Open access LINK [doi:10.1371/journal.pone.0065792]

Abstract

The origins of flora and fauna that are only found in Ireland and Iberia, but which are absent from intervening countries, is one of the enduring questions of biogeography. As Southern French, Iberian and Irish populations of the land snail Cepaea nemoralis sometimes have a similar shell character, we used mitochondrial phylogenies to begin to understand if there is a shared “Lusitanian” history. Although much of Europe contains snails with A and D lineages, by far the majority of Irish individuals have a lineage, C, that in mainland Europe was only found in a restricted region of the Eastern Pyrenees. A past extinction of lineage C in the rest of Europe cannot be ruled out, but as there is a more than 8000 year continuous record of Cepaea fossils in Ireland, the species has long been a food source in the Pyrenees, and the Garonne river that flanks the Pyrenees is an ancient human route to the Atlantic, then we suggest that the unusual distribution of the C lineage is most easily explained by the movements of Mesolithic humans. If other Irish species have a similarly cryptic Lusitanian element, then this raises the possibility of a more widespread and significant pattern.

The evidence gathered by this study is most readily visible in fig. 2:

While it is not the focus of this study, we see here two other cases of probable disjunct distribution:
  • Hg D is found in Iberia, Ireland, small pockets in Britain and SW France but also in North and Central Europe.
  • Hg F shows also disjunct presence in Cornwall, far away from the main cluster around the Bay of Biscay.
The authors of this and previous studies have suggested that this distribution may have to do with intentional transport (as livestock) in the process of the colonization of the Atlantic Islands in the Epipaleolithic. In support of this claim, there is enough fossil evidence of the snail in the island:

Fossil material indicates that this species has been continuously present in Ireland for at least 8000 years (Newlands Cross, Co. Dublin: 7600+/−500 BP Cartronmacmanus, Co. Mayo: 8207+/−165) [7], [8].

In other cases, such as the inedible Kerry slug, we may suspect unintentional transport and therefore we would be justified to imagine a later time frame for their arrival to Ireland, possibly in the Chalcolithic-Megalithic period, but the evidence for C. nemoralis is highly suggestive of intentional transport in the Epipaleolithic. We can therefore say that the humble grove snail was one of the first domestic animals of Europe, possibly second after the dog.
 

Puctuated equilibrium, speciation and everything else

I believe it is worth recommending the reading of this new review paper which discusses the various evolutionary theories en vogue, with emphasis in punctuated equilibrium, which is surely a very realistic model:
Jaroslav Fregg, Microevolutionary, macroevolutionary, ecological and taxonomical implications of punctuational theories of adaptive evolution. Biology Direct 2013. Open accessLINK [doi:10.1186/1745-6150-8-1]

Abstract


Punctuational theories of evolution suggest that adaptive evolution proceeds mostly, or even entirely, in the distinct periods of existence of a particular species. The mechanisms of this punctuated nature of evolution suggested by the various theories differ. Therefore the predictions of particular theories concerning various evolutionary phenomena also differ.


Punctuational theories can be subdivided into five classes, which differ in their mechanism and their evolutionary and ecological implications. For example, the transilience model of Templeton (class III), genetic revolution model of Mayr (class IV) or the frozen plasticity theory of Flegr (class V), suggests that adaptive evolution in sexual species is operative shortly after the emergence of a species by peripatric speciation — while it is evolutionary plastic. To a major degree, i.e. throughout 98-99% of their existence, sexual species are evolutionarily frozen (class III) or elastic (class IV and V) on a microevolutionary time scale and evolutionarily frozen on a macroevolutionary time scale and can only wait for extinction, or the highly improbable return of a population segment to the plastic state due to peripatric speciation.


The punctuational theories have many evolutionary and ecological implications. Most of these predictions could be tested empirically, and should be analyzed in greater depth theoretically. The punctuational theories offer many new predictions that need to be tested, but also provide explanations for a much broader spectrum of known biological phenomena than classical gradualistic evolutionary theories.

I don’t dare to evaluate the paper but I do recommend reading it because it can help us to better understand what is going on when we talk of speciation, competition, evolution, dynamic equilibrium, etc. I picked up this quote:

Approximately 35% of the substitutions (20-70%, depending on the studied taxon) was shown to occur in brief periods of speciation. It is worth mentioning that we are not aware of how many speciation events actually occur in the studied, seemingly unbranched lineages. Therefore, the published estimates of speciation associated substitution rates represent only the lower margin of the real figures.

And the only figure, which illustrates how a highly diverse population/species can be stable and how evolution can happen and often does in bottlenecks instead:
Most punctuational theories of evolution, including the evolutionary conceptions of Wright, Mayr, Carson, Templeton and Flegr (for comparison see Table 1), suggest that sexually reproducing species respond evolutionarily to selection (are evolutionarily plastic) only during speciation. The mechanisms of this type of evolutionary behavior of sexual species suggested by the various theories differ, for a review see [1]. For example, the genetic revolution model [2] implicitly and the frozen plasticity theory explicitly [3] suggest that a species is evolutionary plastic when its members are genetically uniform, i.e. only after a portion of the original species has split off, skirted extinction for several generations, and then undergone rapid multiplication (Figure 1).
The paper uses the “open review” format, including commentaries from the reviewers and the replies by the author – this I find an interesting novelty which adds some value to the paper by pointing possible avenues for discussion or further research.
 
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Posted by on January 17, 2013 in biology, evolution

 

Hominid speciation: sudden or gradual?

It depends apparently: bonobos may have diverged quite suddenly while in other cases, including the Pan-Homo split, the process of speciation appears to have been more gradual.

Thomas Mailund et al., A New Isolation with Migration Model along Complete Genomes Infers Very Different Divergence Processes among Closely Related Great Ape Species. PLoS ONE 2012. Open access LINK [doi:10.1371/journal.pgen.1003125]

Abstract

We present a hidden Markov model (HMM) for inferring gradual isolation
between two populations during speciation, modelled as a time interval
with restricted gene flow. The HMM describes the history of adjacent
nucleotides in two genomic sequences, such that the nucleotides can be
separated by recombination, can migrate between populations, or can
coalesce at variable time points, all dependent on the parameters of the
model, which are the effective population sizes, splitting times,
recombination rate, and migration rate. We show by extensive simulations
that the HMM can accurately infer all parameters except the
recombination rate, which is biased downwards. Inference is robust to
variation in the mutation rate and the recombination rate over the
sequence and also robust to unknown phase of genomes unless they are
very closely related. We provide a test for whether divergence is
gradual or instantaneous, and we apply the model to three key divergence
processes in great apes: (a) the bonobo and common chimpanzee, (b) the
eastern and western gorilla, and (c) the Sumatran and Bornean
orang-utan. We find that the bonobo and chimpanzee appear to have
undergone a clear split, whereas the divergence processes of the gorilla
and orang-utan species occurred over several hundred thousands years
with gene flow stopping quite recently. We also apply the model to the Homo/Pan speciation event and find that the most likely scenario involves an extended period of gene flow during speciation.

 
 

Did the human hand evolve for boxing (too)?

That is the intriguing conclusion of a new study:
Michael H. Morgan and David R. Carrier, Protective buttressing of the human fist and the evolution of hominin hands. The Journal of Experimental Biology, 2012. Freely accessibleLINK [doi: 10.1242/​jeb.075713 ]


Summary

The derived proportions of the human hand may provide supportive
buttressing that protects the hand from injury when striking
with a fist. Flexion of digits 2–5 results in
buttressing of the pads of the distal phalanges against the central palm
and
the palmar pads of the proximal phalanges.
Additionally, adduction of the thenar eminence to abut the dorsal
surface of the
distal phalanges of digits 2 and 3 locks these
digits into a solid configuration that may allow a transfer of energy
through
the thenar eminence to the wrist. To test the
hypothesis of a performance advantage, we measured: (1) the forces and
rate
of change of acceleration (jerk) from maximum
effort strikes of subjects striking with a fist and an open hand; (2)
the static
stiffness of the second metacarpo-phalangeal (MCP)
joint in buttressed and unbuttressed fist postures; and (3) static force
transfer from digits 2 and 3 to digit 1 also in
buttressed and unbuttressed fist postures. We found that peak forces,
force
impulses and peak jerk did not differ between the
closed fist and open palm strikes. However, the structure of the human
fist
provides buttressing that increases the stiffness
of the second MCP joint by fourfold and, as a result of force transfer
through
the thenar eminence, more than doubles the ability
of the proximal phalanges to transmit ‘punching’ force. Thus, the
proportions
of the human hand provide a performance advantage
when striking with a fist. We propose that the derived proportions of
hominin
hands reflect, in part, sexual selection to improve
fighting performance. 
 

I wouldn’t dare to comment much but for what I have read in the paper, it looks plausible, notably because it is indeed significantly efficient versus the open hand (as much as 3x) and because chimpanzees can’t do it… but australopithecines could. 
However I can also imagine this development as a side-effect of other adaptive uses of the hand, such as grabbing a spear, which is no doubt a much more daunting weapon than a naked fist… in most cases at least.
Fig. 2
 
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Posted by on December 20, 2012 in biology, hand, human evolution

 

Ice and "complex organic materials" on Mercury’s poles

This is one of those perplexing astronomical news that make history and I can’t but mention. US scientists have found, with the help of scout satellite MESSENGER,  that not just suspected Mercury’s polar water ice (in shadowed craters) is indeed that but also that confusing dark regions around it are complex organic materials, possibly darkened by the intense solar radiation that bathes the small inner planet. 

The team found that the probe’s reflectance measurements, taken via laser altimetry, matched up well with previously mapped radar-bright regions in Mercury’s high northern latitudes. Two craters in particular were bright, both in radar and at laser wavelengths, indicating the possible presence of reflective ice. However, just south of these craters, others appeared dark with laser altimetry, but bright in radar.

This confused scientists for a while but eventually they realized that the puzzling regions actually hold water ice at a meter’s depth into the soil, where the heat of the sun can’t reach so easily. 
Radar-reflectant regions (ice) show in yellow
The most interesting part however is that the astronomers are almost certain now that the dark material must be complex organic matter, darkened by the extreme solar radiation.
Is there life in Mercury? 
Source: Science Daily.
Ref studies: 
  1. David A. Paige, Matthew A. Siegler, John K. Harmon, Gregory A. Neumann, Erwan M. Mazarico, David E. Smith, Maria T. Zuber, Ellen Harju, Mona L. Delitsky, and Sean C. Solomon. Thermal Stability of Volatiles in the North Polar Region of Mercury. Science, 29 November 2012 DOI: 10.1126/science.1231106
  2. Gregory A. Neumann, John F. Cavanaugh, Xiaoli Sun, Erwan M. Mazarico, David E. Smith, Maria T. Zuber, Dandan Mao, David A. Paige, Sean C. Solomon, Carolyn M. Ernst, and Olivier S. Barnouin. Bright and Dark Polar Deposits on Mercury: Evidence for Surface Volatiles. Science, 29 November 2012 DOI: 10.1126/science.1229764
 
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Posted by on November 30, 2012 in astronomy, biology, chemistry, science, Solar System

 

Elephant hair density helps cooling

The low density of elephant hair has been demonstrated to help cooling:
Conor L. Myrvhold. What Is the Use of Elephant Hair? PLoS ONE 2012. Open access ··> LINK [doi:10.1371/journal.pone.0047018]

At low densities, hair has almost no effect on air flow and does not
trap an insulating air layer near the skin, but the extended hair acts
as a pin fin that increases thermal exchanges with the surrounding air.
Thus, as the hair density decreases from that of very furry animals, a
break-even point is reached where the hair function switches from an
insulator to a heat exchanger. This break-even point occurs at a density
of about 0.3 million hairs/m2 [26] for thick hair covers with creeping flow in between (recall that 1500 hairs/m2 is about the maximum density of elephants). For comparison, the hair density of the human head is about 2 million hairs/m2 (see Methods and Discussion S1).

These heat dispersal properties were already known for plants (leaf hair, cactus’ spines) but it is the first time to be demonstrated for an animal, more specifically a mammal like us. 
Figure 1. Pictures of elephant hair on the top of the back of an Asian elephant, (A) and an African elephant’s head (B).
The presence of hair on elephants was first noted by van Leeuwenhoek
[30]. Photos taken by Conor L. Myhrvold in the Woodland Park Zoo,
Seattle, Washington, from outside of the elephant enclosure, with
permission from the Zoo.
I searched online for hair density on human body (the question we all have in mind, right?) and I could only find a commercial reference (I’d appreciate a better one if you know one). Still it seems that the hair density on tights and legs (and therefore probably on most of the body) in humans is 50 hairs/cm², what translates as 0.5 million hairs/m², somewhat (but not a lot) above the threshold mentioned above.
I’d dare suspect that this means that human body hair (vellus) is for most people thermally neutral but then I wonder how it works with sweat, which is a key part of our tropical thermo-regulatory natural design. Elephants and plants do not sweat (although they do get wet on occasion), so it may well work somewhat different for them.
That seems to be an interesting challenge to explore.
 
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Posted by on November 27, 2012 in Anthropometry, biology, elephants, hair, human evolution