Showing posts with label paleontology. Show all posts
Showing posts with label paleontology. Show all posts

Tuesday 23 June 2020

Grey matter blues: why has the human brain been shrinking?

There is a disturbing fact about our species that the public don't appear to know, and few specialists seem to want to discuss: over recent millennia, the human brain has been shrinking. There have been plenty of non-scientific warnings about the alleged deleterious effects on IQ of first television and more recently smartphones and tablets, but palaeontological evidences proves that over some tens of thousands of years, the Homo sapiens brain has shrunk somewhere between ten and seventeen percent.

There are usually two key indicators said to provide an accurate measure of smartness: encephalisation quotient and absolute brain size. Encephalisation quotient or EQ is simply the ratio of the mass of the brain to the mass of the body. Overall size is seen as critical due to the number of neural connections required for complex thought processes; you can only squeeze so many neurons into any given volume. Having said that, there is some considerably flexibility around this, thanks to variation in neuron density. The reason that some birds, especially the crow and parrot families are highly intelligent despite the small absolute size of their brains is due to their higher neural density compared to mammals.

Analysis of data from the examination of thousands of human fossil remains suggests that our species reached a peak in EQ around 70,000 years ago, followed by a gradual decline. The reduction in brain size appears to be due to a loss of the archetypal grey matter itself, rather than the white matter that provides support to the neural architecture. However, one key issue is lack of agreement as to a definitive start date for this decline, with 20,000 to 40,000 years ago being the most commonly cited origin. With such basic points remaining unsettled, it's perhaps not surprising that there is a plethora of opinions as to the cause. Here are some of the more popular hypotheses for the decline in human brain size:

1. Change to body size

The first and perhaps most obvious - but easily refuted idea - is that human body size has been steadily declining and so cranial capacity has kept in step with this. While it is true that archaic sapiens may have had a higher mass and even stature than modern humans, the reduction in brain size is greater than would be expected when compared to the overall shrinkage. The assumption is that the development of material culture, from clothing to weapons, has given humans a less calorie-demanding lifestyle.

This would allow - although not dictate - natural selection to trend towards a smaller body size. This doesn't appear to offer any help for the comparatively greater reduction in brain mass, although we should remember that an overall reduction in body size means a smaller birth canal. This in turn requires a smaller skull at birth; as is well known, the human gestation period is three months' less than for similar-size mammals, but our seemingly premature delivery is necessary for the pelvis to maintain efficient bipedalism.

2. Self-domestication

Another idea is that humanity has become domesticated via the impact of culture upon natural selection. Following the population bottleneck of 70,000 years ago - the cause of which is not yet confirmed, despite attempts to correlate it with the Toba super-volcano - there has been continual growth of the human population.

Just as all our domesticated animal species have brain sizes some 10-15% smaller than their wild cousins and ancestors, so the move to larger groups sizes may have led to a more docile humanity, with associated traits such as a smaller cranial capacity being carried along with it.

There are several issues with this hypothesis, ranging from a lack of data on the size of gatherer-hunter bands to the biological mechanisms involved. As regards the latter, there has been some speculation concerning neoteny, in which a species no longer grows to the final stage of maturity. The idea is that if adults are more aggressive than juveniles but peaceful collaboration can lead to larger groups, mutual aid and longer lifespans, then unintentional selective breeding for the retention of juvenile characteristics, including smaller brains, may cause a shift away from the fully mature but more aggressive individuals.

Research in recent years has suggested our brains may continuing to grow into our early thirties rather than cease growing in our teens, so it's possible there could be some truth to this; it would interesting to seek evidence as to whether the brains of archaic sapiens continued growing longer than ours do.

3. The impact of culture

Taking this a step further, increased population density allows a more rapid development and transmission of new ideas, including those that lead to better health, longer lifespans and so to an increased birth rate. Culture and sophisticated language may have reduced the need for most people to gain a wide range of skills - courtesy of a higher intellectual capability - as tasks could be shared and specialisation take hold. In effect, larger societies provide a safety net for those who would be less able to cope in smaller groups.

If ideas could be handed down, then individuals wouldn't have to continually 'reinvent the wheel' in each generation, allowing survival despite a smaller brain size and decreased level of intelligence. The problem with this scenario is that we have no proof the 10-17% reduction has led to an associated drop in intellect; it may well be that the size of certain lobes, used in specialist thought processes such as formulating complex speech, far outweigh any decline in less critical areas.

4. The expensive big brain

One possibility that has a clear cause-and-effect concerns the energy demands of having larger brains. Although they consume a quarter of our daily calories, the human brain is less than five per cent of our body weight. Therefore, there could be a case for arguing the existence of an evolutionary competition between smaller-brained individuals who can survive on less food with those who use their larger brains to improve food collecting strategies. Unfortunately, there are so many variables that it's difficult to judge whether the former would continually trend against the latter and - considering it clearly occurred - why the larger brain managed to evolve in the first place?

5. The more efficient brain

Although a smaller brain might have fewer neurons than a larger version with similar architecture, it has been suggested that its shorter pathways would lead to more rapid thought processing than in a larger counterpart. In addition, there might be fewer neural pathways, again increasing the efficiency. This 'nimble thinking' approach certainly seems logical, although again it doesn't explain the evolution of larger EQ in archaic sapiens.

This is certainly a subject ripe for much more research. I've often concluded with a statement along the lines that it wouldn't be surprising if some or all these factors were involved, since nature rarely conforms to the nice, neat patterns we would like to lay upon it. There is an even possibility that brain size - like so many other aspects of all animal species - fluctuates around a mean value, so that what goes up may come down again, only to later go up again.

At least one anthropological study on both Afro-Americans and US citizens of European descent proposes that over the past few hundred years there may have been an upward drift towards larger brains. Assuming the research is accurate, one possibility is that the superior nutrition available since the Industrial Revolution is allowing such development, thanks to the comparative ease with which its energy demands can be fulfilled.

It would certainly be interesting to investigate this hypothesis on a global scale, considering the wide differences between the clinically obese nations and those still subject to frequent famine. Whatever the results, they are unlikely to be the simple 'just-so' stories often passed-off as to the public in lieu of accurate but understandable science communication. The answers may be out there somewhere...I'd certainly love to know what's been happening to the most sophisticated object in the known universe!


Friday 11 January 2019

Hot, cold or in between: thermoregulation and public misunderstanding of science

I recently spotted an intriguing paleontology article concerning the 180 million year old fossil remains of an ichthyosaur, a marine reptile from the Early Jurassic. The beastie, belonging to the genus Stenopterygius,  is so well preserved that it shows coloration patterns (if not the colours themselves) on patches of scaleless skin, as well as a thick layer of insulating fat or blubber. What makes the latter so intriguing is that reptiles just aren't meant to have blubber. Then again, like some snakes and skinks today, ichthyosaurs must have given birth to live young. Thus the gap between reptiles and mammals surely grows ever smaller?

This conundrum touches on some interesting issues about the public's knowledge of science. Several times I've commented on what Richard Dawkins calls the "tyranny of the discontinuous mind", which is the way in which we use categorisation to make it easier to understand the world. It might seem that this is the very essence of some aspects of science, as in New Zealand physicist Ernest Rutherford's famously ungenerous quote that "Physics is the only real science. The rest are just stamp collecting." Indeed, examination of the life and work of many early botanists for example might appear to verify this statement. However, there needs to be an understanding that science requires a flexibility of mind set, a fundamental scientific process being the discarding of a pet theory in favour of a more accurate one.

I'm sure I've remarked countless times - again, echoing Professor Dawkins - that science is in this respect the antithesis of most religions, which set key ideas into stone and refuse to accept any challenges towards them. In the case of the blubber-filled Stenopterygius, it is still a reptile, albeit one that had many of the attributes of mammals. As for the latter, from our pre-school picture books onwards we tend to think of the main mammalian subclass, the placentals, but there are two smaller subclasses: the marsupials, such as the kangaroo; and the monotremes, for example the duck-billed platypus. It has been known since the 1880s that the platypus lays eggs rather than giving birth to live young, a characteristic it shares with the other four monotreme species alive today. In addition, their body temperature is five degrees Celsius lower than that of placental mammals, part of a suite of features presumably retained from their mammal-like reptile ancestors.

Even so, these traits do not justify the comment made by host Stephen Fry in a 2005 episode of the BBC TV quiz show QI, when he claimed that marsupials are not mammals! Richard Dawkins has frequently pointed out that it would be unacceptable to have a similar level of ignorance about the arts as there is on scientific matters, with this being a clear case in point as regards the cultured and erudite Mr Fry. Yet somehow, much of the general public has either a lack or a confusion concerning basic science. Indeed, only  last week I listened to a BBC Radio topical comedy show in which none of the panel members could work out why one face of the moon is always hidden from our view. Imagine the response if it had been a basic lack of knowledge in the arts and literature, for example if an Oxbridge science graduate had claimed that Jane Austen had written Hamlet!

Coming back to the ichthyosaur, one thing we may have learnt as a child is that some animals are warm-blooded and others cold-blooded. This may be useful as a starting point but it is an overly-simplistic and largely outmoded evaluation of the relevant biology; the use of such binary categorisation is of little use after primary school age. In fact, there is series of steps from endothermic homeotherms (encompassing most mammals and birds) to ectothermic poikilotherms (most species of fish, reptiles, amphibians and invertebrates), with the former metabolic feature having evidently developed from the latter.

Ichthyosaurs are likely to have had one of the intermediate metabolisms, as may have been the case for some species of dinosaurs, possibly the smaller, feathered, carnivorous theropods. Likewise, some tuna and shark species are known to be able to produce heat internally, but in 2015 researchers at the US National Marine Fisheries Service announced that five species of the opah fish were found to be whole-body endotherms. Clearly, the boundaries between us supposedly higher mammals and everything else is far less secure than we had previously believed.

At times, science terminology might appear as too abstruse, too removed from the everyday and of little practical use outside of a pub quiz, but then does being able to critique Shakespeare or Charles Dickens help to reduce climate change or create a cure for cancer? Of course we should strive to be fully-rounded individuals, but for too long STEM has been side-lined or stereotyped as too difficult or irrelevant when compared with the humanities.

Lack of understanding of the subtleties and gradations (as opposed to clearly defined boundaries) in science make it easy for anti-science critics to generate public support. Ironically, this criticism tends to take one of two clearly opposing forms: firstly, that science is mostly useless - as epitomised by the Ig Nobel Prize; and alternatively, that it leads to dangerous inventions, as per the tabloid scare-mongering around genetically modified organisms (GMOs) or 'Frankenfoods' as they are caricatured.

Being able to discern nuanced arguments such as the current understanding of animal thermoregulation is a useful tool for all of us. Whether it is giving the public a chance to vote in scientifically-related referendums or just arming them so as to avoid quack medicine, STEM journalism needs to improve beyond the lazy complacency that has allowed such phrases as 'warm-blooded', 'living fossil', 'ice age' and 'zero gravity' to be repeatedly misused. Only then will science be seen as the useful, relevant and above all a much more approachable discipline than it is currently deemed to be.

Monday 27 August 2018

Hammer and chisel: the top ten reasons why fossil hunting is so important

At a time when the constantly evolving world of consumer digital technology seems to echo the mega-budget, cutting-edge experiments of the LHC and LIGO, is there still room for such an old-fashioned, low-tech science as paleontology?

The answer is of course yes, and while non-experts might see little difference between its practice today and that of its Eighteenth and Nineteenth Century pioneers, contemporary paleontology does on occasion utilise MRI scanners among other sophisticated equipment. I've previously discussed the delights of fossil hunting as an easy way to involve children in science, yet the apparent simplicity of its core techniques mask the key role that paleontology still plays in evolutionary biology.

Since the days of Watson and Crick molecular biology has progressed in leaps and bounds, yet the contemporary proliferation of cheap DNA-testing kits and television shows devoted to gene-derived genealogy obscure just how tentatively some of their results should be accepted. The levels of accuracy quoted in non-specialist media is often far greater than what can actually be attained. For example, the data on British populations has so far failed to separate those with Danish Viking ancestry from descendants of earlier Anglo-Saxon immigration, leading to population estimates at odds with the archaeological evidence.


Here then is a list of ten reasons why fossil hunting will always be a relevant branch of science, able to supply information that cannot be supplied by other scientific disciplines:
  1. Locations. Although genetic evidence can show the broad sweeps connecting extant (and occasionally, recently-extinct) species, the details of where animals, plants or fungi evolved, migrated to - and when - relies on fossil evidence.
  2. Absolute dating. While gene analysis can be used to obtain the dates of a last common ancestor shared by contemporary species, the results are provisional at best for when certain key groups or features evolved. Thanks to radiometric dating from some fossiliferous locales, paleontologists are able to fill in the gaps in fossil-filled strata that don't have radioactive mineralogy.
  3. Initial versus canonical. Today we think of land-living tetrapods (i.e. amphibians, reptiles, mammals and birds) as having a maximum of five digits per limb. Although these are reduced in many species – as per horse's hooves – five is considered canonical. However, fossil evidence shows that early terrestrial vertebrates had up to eight digits on some or all of their limbs. We know genetic mutation adds extra digits, but this doesn't help reconstruct the polydactyly of ancestral species; only fossils provide confirmation.
  4. Extinct life. Without finding their fossils, we wouldn't know of even such long-lasting and multifarious groups as the dinosaurs: how could we guess about the existence of a parasaurolophus from looking at its closest extant cousins, such as penguins, pelicans or parrots? There are also many broken branches in the tree of life, with such large-scale dead-ends as the pre-Cambrian Ediacaran biota. These lost lifeforms teach us something about the nature of evolution yet leave no genetic evidence.
  5. Individual history. Genomes show the cellular state of an organism, but thanks to fossilised tooth wear, body wounds and stomach contents (including gastroliths) we have important insights into day-to-day events in the life of ancient animals. This has led to fairly detailed biographies of some creatures, prominent examples being Sue the T-Rex and Al the Allosaurus, their remains being comprehensive enough to identify various pathologies.
  6. Paleoecology. Coprolites (fossilised faeces), along with the casts of burrows, help build a detailed enviromental picture that zoology and molecular biology cannot provide. Sometimes the best source of vegetation data comes from coprolites containing plant matter, due to the differing circumstances of decomposition and mineralisation.
  7. External appearance. Thanks to likes of scanning electron microscopes, fossils of naturally mummified organisms or mineralised skin can offer details that are unlikely to be discovered by any other method. A good example that has emerged in the past two decades is the colour of feathered dinosaurs obtained from the shape of their melanosomes.
  8. Climate analysis. Geological investigation can provide ancient climate data but fossil evidence, such as the giant insects of the Carboniferous period, confirm the hypothesis. After all, dragonflies with seventy centimetre wingspans couldn't survive with today's level of atmospheric oxygen.
  9. Stratigraphy. Paleontology can help geologists trying to sequence an isolated section of folded stratigraphy that doesn't have radioactive mineralogy. By assessing the relative order of known fossil species, the laying down of the strata can be placed in the correct sequence.
  10. Evidence of evolution. Unlike the theories and complex equipment used in molecular biology, anyone without expert knowledge can visit fossils in museums or in situ. They offer a prominent resource as defence against religious fundamentalism, as their ubiquity makes them difficult to explain by alternative theories. The fact that species are never found in strata outside their era supports the scientific view of life's development rather than those found in religious texts (the Old Testament, for example, erroneously states that birds were created prior to all other land animals).
To date, no DNA has been found over about 800,000 years old. This means that many of the details of the history of life rely primarily on fossil evidence. It's therefore good to note that even in an age of high-tech science, the painstaking techniques of paleontology can shed light on biology in a way unobtainable by more recent examples of the scientific toolkit. Of course, the study is far from fool-proof: it is thought that only about ten percent of all species have ever come to light in fossil form, with the found examples heavily skewed in favour of shallow marine environments.

Nevertheless, paleontology is a discipline that constantly proves its immense value in expanding our knowledge of the past in a way no religious text could ever do. It may be easy to understand what fossils are, but they are assuredly worth their weight in gold: precious windows onto an unrecoverable past.

Sunday 15 January 2017

Devoted to dinosaurs: Joan Wiffen and the role of the amateur scientist

I was recently at a second hand book stall, browsing a first edition of Graeme Steven's Prehistoric New Zealand. The market stall owner told me that she had thumbed through the book and was amazed to learn that New Zealand had any wildlife prior to the moa. This seemingly widespread lack of knowledge about the nation's past is no doubt partially due to the small number of both practitioners and finds, although the state education system cannot be considered blameless. Still, in an age of easily-accessible information via the World Wide Web and the likes of the National Geographic Channel, such gaps do seem rather surprising.

Of course a lack of public knowledge concerning ancient life isn't restricted to New Zealand. I recall several amusing (yes, I know it sounds smug) encounters at London's Natural History Museum, where I discovered that parents of dinosaur-crazed children cannot differentiate giant ground sloths from dinosaurs, let alone bipedal carnosaurs from quadrupedal sauropods.

The poor understanding of New Zealand's past is exacerbated by the low population and correspondingly small amount of funding available. Therefore perhaps it's not surprising that amateurs have made significant discoveries, from the Hamilton Junior Naturalist Club's discovery of a giant penguin fossil at Kawhia to Joan Wiffen, the 'Hawke's Bay housewife' (an epithet that always causes me to grit my teeth) who discovered New Zealand's first dinosaur fossils and much more besides.

I've previously discussed the joys of amateur fossicking from a primarily fun aspect but also mentioned how New Zealand relies on non-professionals. The Kawhia penguin is a case in point, as it would have eroded within a year had it not been discovered. Indeed, I was recently collecting some Pleistocene marine molluscs above a Taranaki river valley, on a steep slope prone to severe flooding. These fossils had been uncovered following a landslide caused by a severe rainstorm in 2015 and would no doubt be washed away with the next one.

Fossil hunting in New Zealand

In addition to the lack of professionals, the discipline's funding within New Zealand has decreased over the past half century. The Marsden Fund is a key sponsor of science projects but less than 10% of proposals are successful. The obvious wider issue here is that for the foreseeable future there is unlikely to be any private funding for scientific research that isn't financially viable in the short-term; let's face it, most paleontology isn't going to earn big bucks. That isn't to say there aren't some income streams available, especially around museums, merchandise and occasionally site tourism. However, New Zealand's dinosaur, marine reptile and pterosaur remains are mostly isolated fragments, hardly likely to prove star attractions for even the most ardent dino enthusiast.

Which brings us back to Joan Wiffen. She went from a minimal secondary education (due to her father's prejudice) to an honorary science degree from Massey University - whilst still supporting the view that it is the duty of married women to do all the housework. Although she may not have actively negated the Hawke's Bay housewife appellation, the term is hardly suitable for an extremely conscientious scientist; after all, if her husband had been the team leader, he probably wouldn't have been referred to as a Hawke's Bay electronics technician!

Having recently finished reading Wiffen's 1991 book Valley of the Dragons: The Story of New Zealand's Dinosaur Woman I was struck by the obvious lack of professional expertise available in New Zealand as recently as the 1970s and 1980s. Even today, the thirty or so professional paleontologists in the country don't have their own organisation and fall under the auspices of the Geoscience Society of New Zealand. Yet I've long considered geology to be an extremely conservative discipline (think that meteorologist Alfred Wegener's continental drift hypothesis gained little traction for decades until evidence of plate tectonics was found, rather than there being any active interest in resolving the mystery) and so can do few favours to outsiders.

Therefore, Joan Wiffen faced almost complete indifference from scientists who proclaimed there were no relevant strata in which to locate dinosaur remains. Apparently someone had previously noticed reptilian bones in a Te Hoe Valley stream bed - which is what sparked off Wiffen's first expedition - but no-one had the interest or funding to follow it up. Her narrative hints at the disdain professionals felt for amateurs in general but happily this situation has changed markedly in the interim, with citizen science helping to bridge gaps in many fields. In the case of New Zealand paleontology, the notable finds by amateurs have included previously unknown species, adding to the evidence that areas of the 'lost' continent of Zealandia have been continually above water since the Mesozoic.

My recent Taranaki excursion was child's play compared to the deprivations Wiffen and co endured in their rat-infested self-built hut, not to mention funding the entire work themselves. From learning how to remove rock matrix via acetic acid (in an old baby bath, no less) to building a stereo microscope stand from a pillar drill base, the Hawke's Bay team certainly utilised classic kiwi number eight wire ingenuity.

In a pre-internet age - it took six months just to pin down the location and land owner of the area marked 'reptile bones' - gaining technical advice from foreign experts was slow and cumbersome. Ironically, in later years New Zealand professionals visited Wiffen's fossil preparation workshop to gain insight into their operation, including as to how she and her friends achieved such high standards. Clearly, her work wasn't the product of a casual dilettante but the output of a highly motivated and hard-working scientist, albeit an unpaid one.

The American paleontologist and evolutionary biologist Stephen Jay Gould frequently observed that his disciplines were forms of historical science, built upon a series of unrepeatable events created by the complex interaction of disparate factors. Therefore deposition and preservation - even the discovery - of fossils are unique circumstances; remains that are visible today may be little more than dust tomorrow. We owe Joan Wiffen and her colleagues an enormous debt for increasing the sum of human knowledge at their own time and expense, purely for the love of science. And if any Hawke's Bay residents want to pick up where she left off, then I'm sure both professionals and posterity would be most grateful!