Recent Discoveries in Human Evolution: H. Sapiens 300,000 years old?

Welcome back to our discussion of recent exciting advances in our knowledge of human evolution:

  • Ancient hominins in the US?
  • Homo naledi
  • Homo flores
  • Humans evolved in Europe?
  • In two days, first H Sap was pushed back to 260,000 years,
  • then to 300,000 years!
  • Bell beaker paper

As we’ve been discussing for the past couple of weeks, the exact dividing line between “human” and “non-human” isn’t always hard and fast. The very first Homo species, such as Homo habilis, undoubtedly had more in common with its immediate Australopithecine ancestors than with today’s modern humans, 3 million years later, but that doesn’t mean these dividing lines are meaningless. Homo sapiens and Homo neandethalensis, while considered different species, interbred and produced fertile offspring (most non-Africans have 3-5% Neanderthal DNA as a result of these pairings;) by contrast, humans and chimps cannot produce fertile offspring, because humans and chimps have a different number of chromosomes. The genetic distance between the two groups is just too far.

Oldowan tool

The grouping of ancient individuals into Homo or not-Homo, Erectus or Habilis, Sapiens or not, is partly based on physical morphology–what they looked like, how they moved–and partly based on culture, such as the ability to make tools or control fire. While australopithecines made some stone tools (and chimps can make tools out of twigs to retrieve tasty termites from nests,) Homo habilis (“handy man”) was the first to master the art and produce large numbers of more sophisticated tools for different purposes, such as this Oldowan chopper.

But we also group species based on moral or political beliefs–scientists generally believe it would be immoral to say that different modern human groups belong to different species, and so the date when Homo ergaster transforms into Homo sapiens is dependent on the date when the most divergent human groups alive today split apart–no one wants to come up with a finding that will get trumpeted in media as “Scientists Prove Pygmies aren’t Human!” (Pygmies already have enough problems, what with their immediate neighbors actually thinking they aren’t human and using their organs for magic rituals.)

(Of course they would still be Human even if they part of an ancient lineage.)

But if an ecologically-minded space alien arrived on earth back in 1490 and was charged with documenting terrestrial species, it might easily decide–based on morphology, culture, and physical distribution–that there were several different Homo “species” which all deserve to be preserved.

But we are not space aliens, and we have the concerns of our own day.

So when a paper was published last year on archaic admixture in Pygmies and the Pygmy/Bushmen/everyone else split, West Hunter noted the authors used a fast–but discredited–estimate of mutation rate to avoid the claim that Pygmies split off 300,000 years ago, 100,000 years before the emergence of Homo sapiens:

There are a couple of recent papers on introgression from some quite divergent archaic population into Pygmies ( this also looks to be the case with Bushmen). Among other things, one of those papers discussed the time of the split between African farmers (Bantu) and Pygmies, as determined from whole-genome analysis and the mutation rate. They preferred to use the once-fashionable rate of 2.5 x 10-8 per-site per-generation (based on nothing), instead of the new pedigree-based estimate of about 1.2 x 10-8 (based on sequencing parents and child: new stuff in the kid is mutation). The old fast rate indicates that the split between Neanderthals and modern humans is much more recent than the age of early Neanderthal-looking skeletons, while the new slow rate fits the fossil record – so what’s to like about the fast rate? Thing is, using the slow rate, the split time between Pygmies and Bantu is ~300k years ago – long before any archaeological sign of behavioral modernity (however you define it) and well before the first known fossils of AMH (although that shouldn’t bother anyone, considering the raggedness of the fossil record).

This was a good catch. (Here is the relevant Dienekes article, plus Model-based analyses of whole-genome data reveal a complex evolutionary history involving archaic introgression in Central African Pygmies, and Whole-genome sequence analyses of Western Central African Pygmy hunter-gatherers reveal a complex demographic history and identify candidate genes under positive natural selection.) If the slow mutation rate matches the fossil record better than the fast, why use the fast–except if the fast gives you inconvenient results?

But now we have another finding, based on the Bushmen, which also pushes the Bushmen/everyone else split back further than 200,000 years–from BioRxiv, “Ancient genomes from southern Africa pushes modern human divergence beyond 260,000 years ago“:

Southern Africa is consistently placed as one of the potential regions for the evolution of Homo sapiens. To examine the region’s human prehistory prior to the arrival of migrants from East and West Africa or Eurasia in the last 1,700 years, we generated and analyzed genome sequence data from seven ancient individuals from KwaZulu-Natal, South Africa. Three Stone Age hunter-gatherers date to ~2,000 years ago, and we show that they were related to current-day southern San groups such as the Karretjie People. Four Iron Age farmers (300-500 years old) have genetic signatures similar to present day Bantu-speakers. The genome sequence (13x coverage) of a juvenile boy from Ballito Bay, who lived ~2,000 years ago, demonstrates that southern African Stone Age hunter-gatherers were not impacted by recent admixture; however, we estimate that all modern-day Khoekhoe and San groups have been influenced by 9-22% genetic admixture from East African/Eurasian pastoralist groups arriving >1,000 years ago, including the Ju|’hoansi San, previously thought to have very low levels of admixture. Using traditional and new approaches, we estimate the population divergence time between the Ballito Bay boy and other groups to beyond 260,000 years ago.

260,000 years! Looks like West Hunter was correct, and we should be looking at the earlier Pygmy divergence date, too.

Two days later, a paper from the opposite end of Africa appeared in Nature which–potentially–pushes H sapiens’s emergence to 300,000 years ago, “New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens“:

Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure … In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315 ± 34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established.

Comparison of the skulls of a Jebel Irhoud human (left) and a modern human (right) (NHM London)

Hublin–one of the study’s coauthors–notes that between 330,000 and 300,000 years ago, the Sahara was green and animals could range freely across it.

While the Moroccan fossils do look like modern H sapiens, they also still look a lot like pre-sapiens, and the matter is still up for debate. Paleoanthropologist Chris Stringer suggests that we should consider all of our ancestors after the Neanderthals split off to be Homo sapiens, which would make our species 500,000 years old. Others would undoubtedly prefer to use a more recent date, arguing that the physical and cultural differences between 500,000 year old humans and today’s people are too large to consider them one species.

According to the Atlantic:

[The Jebel Irhoud] people had very similar faces to today’s humans, albeit with slightly more prominent brows. But the backs of their heads were very different. Our skulls are rounded globes, but theirs were lower on the top and longer at the back. If you saw them face on, they could pass for a modern human. But they turned around, you’d be looking at a skull that’s closer to extinct hominids like Homo erectus. “Today, you wouldn’t be able to find anyone with a braincase that shape,” says Gunz.

Their brains, though already as large as ours, must also have been shaped differently. It seems that the size of the human brain had already been finalized 300,000 years ago, but its structure—and perhaps its abilities—were fine-tuned over the subsequent millennia of evolution.

No matter how we split it, these are exciting days in the field!

Distance, Surface, Electrodynamics of Moving Bodies: A Relativistic Critique of Maxwellcentric Conceptions of “Knowing” Bodies

Note: This post, What if Famous Scientists Wrote like Gender Scholars? originally appeared as a guest post on Lawrence Glarus’s blog.

Have you ever wondered what famous math/science works would sound like if they had been written by gender scholars? Then today is your lucky day!

I. Distance, Surface, Electrodynamics of Moving Bodies: A Relativistic Critique of Maxwellcentric Conceptions of “Knowing” Bodies, by A. Einstein

In Philosophiæ Naturalis Principia Mathematica, Isaac Newton examines the sensory and cognitive, mathematical processes involved in rendering bodies in motion as remaining in motion and bodies at rest as remaining at rest, using the language of infinitessimal, geometric calculus. Maxwellcentric social norms emphasize differences, rather than similarities, between moving electrodynamic bodies, creating perceptions of asymmetries which do not appear to be inherent in the phenomena. In this paper I focus on a particular subjectivity and a particular spatiality. The subjectivity is that of dominant Western Maxwellcentric electrodynamics. The spatiality is the specific organisation of spacetime through which that subjectivity is constituted and through which it sees the world, a problematic described here as a relativistic space of electrodynamic self/knowledge. Take, for example, the reciprocal, non-patriarchal electrodynamic action of a magnet (“masculine”) and a conductor (“feminine”). By introducing the “infinitessimal” metaphor, Newton enables theoretical development in how cultural norms and sensory perceptions shape the social construction of spacetime curvature around the action of the magnet and conductor. The observable phenomenon here depends only on the relative motion of the conductor and the magnet, whereas the customary, phallocentric, Maxwellian view draws a sharp, “othering” distinction between the two cases in which either the one or the other of these bodies is in motion.  In the process of electrodynamic attribution, cognitive filters guide our attention to certain features of bodies marked as different (e.g., spin, charge, mass), while priming us to ignore other features of bodies (e.g., shape, velocity). The move from a structuralist account in which “electricity” is understood to structure activities between magnets and conductors in relatively homologous way to a view of hegemony in which electrodynamic powers are subject to repetition, convergence, and rearticulation brought the question of temporality into the thinking of space structure, and marked a shift from a form of Maxwellian theory that takes structural, atomic totalities as theoretical objects (eg, photons, electrons,) to one in which the insights into the contingent possibility of unified spacetime structures inaugurate a renewed conception of electrodynamics as bound up with contingent bodies.

It is thus argued that certain psychoanalytic Newtonian electrodynamic theories—like all psychodynamic mathematics—can offer a critical account of Maxwellcentric kinematics of the rigid body, since the assertions of any such theory have to do with the relationships between rigid bodies (systems of co-ordinates), clocks, and electromagnetic processes, which is also a critical account of the production of visual space-time interactions. Insufficient consideration of this circumstance lies at the root of the difficulties which the electrodynamics of moving bodies at present encounters. …

 

II. The Construction of Shapes as a Quintessentially Masculine Subject: The Elements of Geometric Gender, by Euclid of Alexandria

Definition 1.
A point is that which has no gender, ergo, is invisible to cisheteronormative ways of “seeing.”

Definition 2.
A line is conceptualized by Freudian psychodynamics as a phallus.

Definition 3.
The ends of a line are points, an imposition of patriarchal masculinization upon a formerly a-gendered space.

Definition 4.
A straight line is a line which has internalized cis-hetero-normative expectations of psychodynamic sexual relations between “men” and “women,” producing an arbitrary gender binary that contributes to the erasure and oppression of non-binary performing individuals.

Definition 5.
A surface is that which presents the illusion of impenetrability along its length and breadth, except by the masculine, heteronormative phallus, reinforcing colonialist narratives of the importance of male dominance.

Definition 6.
The edges of a surface are an a-structural post-colonist region of conceptualized “boundaries” between “masculine” and “feminine”.

Definition 7.
A plane surface is an unbounded, limitless potentiality-space which lies evenly with the conception of heteronormaty imposed on itself.

Definition 8.
A plane angle is the homosexual inclination to one another of two lines (constructed masculinities) in a plane which meet one another and hereafter reject heteronormative coupling with non-angles.

Definition 9.
And when the lines containing the angle are viewed through the lens of patriarchal heteronormativity, the angle is called recti-(ie, rectum)-linear (ie, phallus.)

Definition 10.
When a straight line standing on a straight line oppresses the adjacent angles, subverting their equality to one another, each of the equal angles is justified in its demand for self-expression, and the straight line standing on the other is called an oppressor (capitalist, bourgeois,) to that on which it stands (the subject, colonized, feminized “other.”) …

 

III. On the Deconstruction of “Species” as a “Natural” category: a Feminist Approach to re-imagining the Descent of (Hu)”man” Outside the Patriarchal Supremacy Paradigm, by C. Darwin

Chapter 1: Variation Under Domestication

Unquestioned patriarchic thought modes employ explicit categorization of living beings into unchanging, discreet hierarchies, from beast to angel, placing man–qua man–in the topmost, “in the image of god,” (the masculine) position. In this paper, I draw upon the theories of Buffon, Lamarck, Saint-Hilaire, Wells, Herbert, and others to develop a counter-narrative, feminist proposal that nature (“feminine,” but against patriarchal codings, red in tooth and claw, not maternal,) is the source of selective pressures that gradually transform one species into another.

When on board H.M.S. Beagle, as a queer-identified trans-racial feminist, I was much struck with certain facts in the distribution of the oppressed, post/colonial indigenous persons of color of South America, and in the geological relations of the present to the past inhabitants of that continent. The constructed masculinities of domination embodied by the colonist sphere struck me as throwing light upon the sharp, hierarchical divisions between beings which lead to my revelation that change, over time, could account for the origins of that which we insist on calling “species.”

When we examine the effects of patriarchal subjugation and domination of plant and animal forms for the satisfaction of human appetites, we are struck forcefully by the great diversity of outcomes: the domesticated, “husbanded” forms differ much more from each other, than do the individuals of any one species or variety in a state of natural, feminine, stewardship. When we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, I think we are driven to conclude that this greater variability is due to man’s (masculine) drive to divide, differentiate, subdue, and consume. Even our oldest cultivated, “domesticated”–as in domestic, housewife, feminine, dominated by the patriarchal–varieties of plants and animals such as wheat, are still often driven to produce new varieties or “improvements” that exist, of course, only for improving their economy or taste on a human’s palate, not for marked change in the individual being’s experience of life or joy. …

 

I hope you all enjoyed reading those as much as I enjoyed writing them.

With apologies to Albert Einstein’s On the Electrodynamics of Moving Bodies, Euclid’s Elements, Charles Darwin’s On The Origin of Species by Natural Selection, and Isaac Newton’s Philosophiæ Naturalis Principia Mathematica.

With no apologies to: Blind to Sameness: Sexpectations and the Social Construction of Male and Female Bodies, Distance, Surface, Elsewhere: A Feminist Critique of the Space of Phallocentric Self/Knowledge, The Construction of Physics as a Quintessentially Masculine Subject: Young People’s Perceptions of Gender Issues in Access to Physics, Science: A Masculine Disorder? or Judith Butler.

And with special thanks to Lawrence Glarus for hosting me and to Twitter’s NewRealPeerReview for curating the list of atrocious (but real) papers that inspired this post.