Showing posts with label hominin. Show all posts
Showing posts with label hominin. Show all posts

Tuesday 12 May 2020

Ancestral tales: why we prefer fables to fact for human evolution

It seems that barely a month goes by without there being a news article concerning human ancestry. In the eight years since I wrote a post on the apparent dearth of funding in hominin palaeontology there appears to have been some uptake in the amount of research in the field. This is all to the good of course, but what is surprising is that much of the non-specialist journalism - and therefore public opinion - is still riddled with fundamental flaws concerning both our origins and evolution in general.

It also seems that our traditional views of humanity's position in the cosmos is often the source of the errors. It's one thing to make such howlers as the BBC News website did some years' back, in which they claimed chimpanzees were direct human ancestors, but there are a key number of more subtle errors that are repeated time and again. What's interesting is that in order to explain evolution by natural selection, words and phrases have become imbued with incorrect meaning or in some cases, just a slight shift of emphasis. Either way, it seems that evolutionary ideas have been tacked onto existing cultural baggage and in the process, failed to explain the intended theories; personal and socio-political truths have triumphed over objective truth, as Neil deGrasse Tyson might say.

1) As evolutionary biologist Stephen Jay Gould use to constantly point out, the tree of life is like the branches of a bush, not a ladder of linear progression. It's still fairly common to see the phrase 'missing link' applied to our ancestry, among others; I even saw David Attenborough mention it in a tv series about three years' ago. A recent news article described - as if in surprise - that there were at least three species of hominins living in Africa during the past few million years, at the same time and in overlapping regions too. Even college textbooks use it - albeit in quotation marks - among a plethora of other phrases that were once valid, so perhaps it isn't surprising that popular publications continue to use them without qualification.

Evolution isn't a simple, one-way journey through space and time from ancestors to descendants: separate but contemporaneous child species can arise via geographical isolation and then migrate to a common location, all while their parent species continues to exist. An example today would be the lesser black-backed and herring gulls of the Arctic circle, which is either a single, variable species or two clearly distinct species, depending where you look within its range.

It might seem obvious, but species also migrate and then their descendants return to the ancestral homeland; the earliest apes evolved in Africa and then migrated to south-east Asia, some evolving into the ancestors of gibbons and orangutan while others returned to Africa to become the ancestors of gorillas and chimpanzees. One probable culprit of the linear progression model is that some of the examples chosen to teach evolution such as the horse have few branches in their ancestry, giving the false impression of a ladder in which a descendant species always replaces an earlier one.

2) What defines a species is also much misunderstood. The standard description doesn't do any favours in disentangling human evolution; this is where Richard Dawkins' oft-repeated phrase 'the tyranny of the discontinuous mind' comes into play. Examine a range of diagrams for our family tree and you'll find distinct variations, with certain species sometimes being shown as direct ancestors and sometimes as cousins on extinct branches.

If Homo heidelbergensis is the main root stock of modern humans but some of us have small amounts of Neanderthal and/or Denisovan DNA, then do all three qualify as direct ancestors of modern humans? Just where do you draw the line, bearing in mind every generation could breed with both the one before and after? Even with rapid speciation events between long periods of limited variability (A.K.A. punctuated equilibrium) there is no clear cut-off point separating us from them. Yet it's very rare to see Neanderthals labelled as Homo sapiens neanderthalensis and much more common to see them listed as Homo neanderthalensis, implying a wholly separate species.

Are the religious beliefs and easy-to-digest just-so stories blinding us to the complex, muddled background of our origins? Obviously, the word 'race' has profoundly negative connotations these days, with old-school human variation now known to be plain wrong. For example, there's greater genetic variation in the present-day sub-Saharan African population than in the rest of the world combined, thanks to it being the homeland of all hominin species and the out-of-Africa migrations of modern humans occurring relatively recently.

We should also consider that species can be separated by behaviour, not just obvious physical differences. Something as simple as the different pitches of mating calls separate some frog species, with scientific experiments proving that the animals can be fooled by artificially changing the pitch. Also, just because species appear physically similar doesn't necessarily mean an evolutionary close relationship: humans and all other vertebrates are far closer to spiny sea urchins and knobbly sea cucumbers than they are to any land invertebrates such as the insects.

3) Since the Industrial Revolution, societies - at least in the West - have become obsessed with growth, progress and advance. This bias has clearly affected the popular conception that evolution always leads to improvements, along the lines of faster cheetahs to catch more nimble gazelles and 'survival of the fittest'. Books speak of our epoch as the Age of Mammals, when by most important criteria we live in the era of microbes; just think of the oxygen-generating cyanobacteria. Many diagrams of evolutionary trees place humans on the central axis and/or at the pinnacle, as if we were destined to be the best thing that over three billion years of natural selection could achieve. Of course, this is no better than what many religions have said, whereby humans are the end goal of the creator and the planet is ours to exploit and despoil as we like (let's face it, for a large proportion of our existence, modern Homo sapiens was clearly less well adapted to glacial conditions than the Neanderthals).

Above all, these charts give the impression of a clear direction for evolution with mammals as the core animal branch. Popular accounts still describe our distant ancestors, the synapsids, as the 'mammal-like reptiles', even though they evolved from a common ancestor of reptiles, not from reptiles per se. Even if this is purely due to lazy copying from old sources rather than fact-checking, doesn't it belie the main point of the publication? Few general-audience articles admit that all of the earliest dinosaurs were bipedal, presumably because we would like to conflate standing on two legs with more intelligent or 'advanced' (a tricky word to use in a strict evolutionary sense) lineages.

The old ladder of fish-amphibian-reptile/bird-mammal still hangs over us and we seem unwilling to admit to extinct groups (technically called clades) that break our neat patterns. Incidentally, for the past 100 million years or so, about half of all vertebrate species have been teleost fish - so much for the Age of Mammals! No-one would describe the immensely successful but long-extinct trilobites as just being 'pill bug-like marine beetles' or similar, yet when it comes to humans, we have a definite sore spot. There is a deep psychological need to have an obvious series of ever-more sophisticated ancestors paving the way for us.

What many people don't realise is that organisms frequently evolve both physical and behavioural attributes that are subsequently lost and possibly later regained. Some have devolved into far simpler forms, frequently becoming parasites. Viruses are themselves a simplified life form, unable to reproduce without a high-jacked cell doing the work for them; no-one could accuse them of not being highly successful - as we are currently finding out to our cost. We ourselves are highly adaptable generalists, but on a component-by-component level it would appear that only our brains make us as successful as we are. Let's face it, physically we're not up to much: even cephalopods such as squid and octopus have a form of camera eye that is superior to that of all vertebrates.

Even a cursory glance at the natural history of life, using scientific disciplines as disparate as palaeontology and comparative DNA analysis, shows that some lineages proved so successful that their outward physiology has changed very little. Today, there are over thirty species of lancelet that are placed at the base of the chordates and therefore closely related to the ancestors of all vertebrates. They are also extremely similar in appearance to 530-million-year-old fossils of the earliest chordates in the Cambrian period. If evolution were a one-way ticket to progress, why have they not long since been replaced by later, more sophisticated organisms?

4) We appear to conflate success simply with being in existence today, yet our species is a newcomer and barely out of the cradle compared to some old-timers. We recently learned that Neanderthals wove plant fibre to make string and ate a wide variety of seafood. This knowledge brings with it a dwindling uniqueness for modern Homo sapiens. The frequently given explanation of our superiority over our extinct cousins is simply that they aren't around anymore, except as minor components of our genome. But this is a tautology: they are inferior because they are extinct and therefore an evolutionary dead end; yet they became extinct because of their inferiority. Hmmm...there's not much science going on here!

The usual story until recently was that at some point (often centred around 40,000-50,000 years ago) archaic sapiens developed modern human behaviour, principally in the form of imaginative, symbolic thinking. This of course ignores the (admittedly tentative) archaeological evidence of Neanderthal cave-painting, jewelry and ritual, all of which are supposed to be evidence of our direct ancestor's unique Great Leap Forward (yes, it was named after Chairman Mao's plan). Not only did Neanderthals have this symbolic behaviour, they appear to have developed it independently of genetically-modern humans. This is a complete about-turn from the previous position of them being nothing more than poor copyists.

There are alternative hypotheses to the Great Leap Forward, including:
  1. Founder of the Comparative Cognition Project and primate researcher Sarah Boysen observed that chimpanzees can create new methods for problem solving and processing information. Therefore, a gradual accumulation of cognitive abilities and behavioural traits over many millennia - and partially inherited from earlier species - may have reached a tipping point. 
  2. Some geneticists consider there to have been a sudden paradigm shift caused by a mutation of the FOXP2 gene, leading to sophisticated language and all that it entails.
  3. Other researchers consider that once a certain population size and density was achieved, complex interactions between individuals led the way to modern behaviour. 
  4. A better diet, principally in the form of larger amounts of cooked meat, led to increased cognition. 
In some ways, all of these are partly speculative and as is often the case we may eventually find that a combination of these plus other factors were involved. This shouldn't stop us from realising how poor the communication of evolutionary theories still is and how many misconceptions exist, with the complex truth obscured by our need to feel special and to tell simple stories that rarely convey the amazing evolution of life on Earth.



Thursday 27 October 2016

Murky waters: why is the aquatic ape hypothesis so popular?


Whilst not in the same class as the laughably abysmal Discovery Channel mockumentaries on the likes of mermaids and extant (rather than extinct) megalodon, the recent two-part David Attenborough BBC Radio 4 documentary The Waterside Ape has left me gritting my teeth...grrr.

The programme has confirmed something I suspected from his 2010 BBC television series and associated book, First Life: namely, that the style of his exposition takes priority over the substance of his material. I'll quickly recap on the howler he made in an episode of First Life, ironically one that featured renowned trilobite expert Richard Fortey, albeit in a different sequence. When discussing trilobites, Sir David briefly mentions that they get their name from having three segments from front to rear: head, body and pygidium (tail) - which is totally wrong!

The name is the give-away. Tri-lobe refers to the three segments across the width of the body: a central lobe and two lateral lobes. Many creatures have the head, body and tail segmentation, so it would be far from unique in trilobites. I find this example of incorrect information rather discomforting, especially from someone like Sir David who has been a fan of trilobites since childhood. You have to wonder why experts aren't invited to give BBC science and nature documentaries the once-over before broadcast, just in case any gaffes have got through to the final cut?

The issue then, is that if we non-professionals believe the content espoused by such senior figures in the field of science communication - and if such material goes without basic error-checking from professionals - how is the public to receive a half-decent science education? Of course science isn't a body of knowledge but a toolkit of investigation techniques, but few of the general public have the ability to test hypotheses themselves or access the jargon-filled original scientific papers. So relying on books and media from distinguished communicators is the primary way of increasing our STEM (Science, Technology, Engineering and Mathematics) knowledge.

Back to The Waterside Ape. The hypothesis is an old one, dating back to marine biologist - and let's face it, oddball theorist - Sir Alister Hardy's first, unpublished speculations in 1930. However, the idea didn't achieve widespread dissemination until Elaine Morgan began to publicise it in the early 1970's. Otherwise known as a fiction writer, Morgan's output on the aquatic ape hypothesis was originally considered to be a feminist critique rather than particularly serious science, bearing in mind that the author lacks professional training or experience in the field of evolutionary biology.

Whether it is thanks to dissemination via the World Wide Web, her pro-aquatic ape books have become ever more popular over the past twenty years. This is in spite of the ever-increasing number of hominin fossils and sophisticated analytical techniques that have shown little support for the idea. I'm not going to examine the evidence for and against the hypothesis, since that has been done by many others and I'm marginally less qualified to assess it than Elaine Morgan. Instead, I'm more interested in how and why the idea has maintained popular appeal when the general consensus among the specialists is that it is profoundly incorrect.

Could it be that the engaging quality of Morgan's writing obscures a lack of dry (geddit?) analysis upon a subject that could at best be deemed as controversial - and thus fool the general readership as to its validity? Or is there more to it than that? The BBC seem to have maintained an on-going interest in supporting her work over the past two decades.

Indeed, The Waterside Ape is not David Attenborough's first foray into the idea. He made another two-part BBC Radio 4 series called Scars of Evolution back in 2005, which included some of the same interviews as the recent programmes. The BBC and Discovery Channel also collaborated in 1998 on a television documentary favouring the hypothesis called surprisingly enough The Aquatic Ape, albeit without Attenborough's involvement.

A key argument that I'm sure gets public support is that the of a radical - and female - outsider being shunned by the conservative, male-dominated establishment, with Elaine Morgan pitted against the reactionary old guard of palaeontologists, biologists, etc. Her plight has been described in the same vein as meteorologist Alfred Wegener's battle with orthodox geology between the world wars, but in Wegener's case his hypothesis of continental drift lacked a mechanism until plate tectonics was formulated several decades later. As for the aquatic ape, there seems to be a suite of models describing a gamut of ideas, from the uncontroversial speculation of hominins wading for iodine- and Omega-3-rich foodstuffs (promoting brain growth) to human ancestors being Olympic-class ocean swimmers who would feel at home in a Discovery Channel mermaid mockumentary.

We shouldn't ignore the emotive aspects of the hypothesis, which the various programmes have described as a "fascinating idea" that would be "lovely to confirm". Since most people still think of dolphins as innocent, life-saving and cute (when in fact they play brutal cat-and-mouse games with live porpoises) could this be a psychological attempt to salvage something of our own rapacious species?

Elaine Morgan admitted that her first book was a response to her annoyance with the 'killer ape' theories of the 1960's, as espoused in Robert Ardrey's seminal 1961 volume African Genesis. In these post-modern, politically-correct times of gatherers first and hunters second, Raymond Dart and Robert Ardrey's once-influential machismo ape-man has fallen from favour. Unfortunately, the famous Ardrey-influenced Dawn of Man sequence in 2001: A Space Odyssey promotes just such a viewpoint, so perhaps it isn't any wonder that supporting a more tranquil aquatic ancestry might appear to be an easy way to bring 21st century sensitivities to a world reeling from constant violence.

Another possible reason for the hypothesis' widespread support is that it relies on what appears to be an impressive accumulation of facts in the Darwinian mould, without recourse to difficult mathematics or sophisticated technical jargon. For those unable to get a clear understanding of major contemporary science (Higgs boson, anyone?) the idea of aquatic ape ancestors is both romantic and easy to digest, if the supporting evidence is taken en masse and the individual alternatives for each biological feature ignored or undeclared.

Clearly, whoever thinks that science is detached from emotion should think again when considering the aquatic/waterside/paddle-boarding ape. Although on the surface a seductive idea, the collection of proofs are selective, inadequate and in some cases just plain wrong. It might be good enough for the sloppy pseudo-scientific archaeology of Graham Hancock and Erich von Daniken, but good science needs rather more to go on. Yes, there are some intriguing nuggets, but as Dr Alice Roberts said in her critique of the recent Attenborough radio series, science is about evidence, not wishful thinking. Unfortunately, the plethora of material contains rather more subtleties than trilobite nomenclature, so I can only sigh again at just how many equally poorly-concocted ideas may be swashing around the world of popular science communication. Come on, Sir David, please read past the romance and dig a bit deeper: the world needs people like you!