Why Do We Care About Human Evolution Today?

Tattersall Fig 1 Tree (cropped) (resize)Detail from author

Wherever our origins ultimately lie, there is no rational doubt that we Homo sapiens are proximally the product of an eventful evolutionary past.  Our ancient history is richly documented by a fossil record that is remarkably abundant for one single family of primates, and that is certainly a lot better than most paleoanthropologists are prepared to concede as they write funding proposals for more fossil exploration.  Saying this is not, of course, to deny the huge value of such exploration.  Fossil records are by their nature incomplete, and in a science in which every answer leads to compelling new questions, it is important to flesh them out as much as possible.

Still, what we already know allows us to construct a fairly convincing outline sketch of human prehistory, and of the natural context in which it played out.  What’s more, as members of an intensely curious species that instinctively wants to know the “why” of everything, most of us are naturally interested in knowing more about this drama of human becoming.  But in trying to learn as much as possible about our evolutionary background, are we merely satisfying an innate genealogical inquisitiveness?  Or can we take this enterprise beyond the satisfaction of superficial curiosity, to discover more profound implications about ourselves and our essential natures?  I would argue that we can, and indeed that only by knowing the nature of the process that produced us can we begin to understand the rather bizarre and contradictory ways in which humans sometimes behave.

Several years ago, I attracted some mostly good-natured ribbing from friends and colleagues by arguing that we can learn nothing about human nature from studying the deep human past that we cannot learn by looking around at ourselves today, in all our murky complexities.  And while this claim might seem rather an odd one for a paleoanthropologist to make, I still believe there is truth in it.  Our species is fully integrated into the Great Tree of Life that unites all living things.  But there is nonetheless something about the way in which modern Homo sapiens mentally processes information that makes our species qualitatively different from all other creatures, including our own evolutionary predecessors.  In purely historical terms, we are not simply an extrapolation of any trends those predecessors might have embodied.  Still, the emergent nature of our cognitive processes most emphatically does not mean that there is no value in closely scrutinizing the long process that produced us.

Why Evolution Matters

This is because the exact manner of our evolution cuts straight to the heart of who we are.  There are basically two possibilities here.  If our biological history consisted simply of the gradual modification of a central hominid lineage over the eons, as most of us were taught in school (if evolution was mentioned at all), then we might legitimately conclude that natural selection has in some sense fine-tuned us to an identifiable human condition.  This would certainly be the clear implication if our fossil and archaeological records were to show that slow and steady biological and technological change was the rule among our extinct predecessors.  But if, in contrast, those records were in fact to reveal a picture of diversity and morphological experimentation, interspersed with periods of nothing much happening, the inference would be entirely otherwise.  If we were to find a bewildering variety of hominid species, all buffeted over time by the vagaries of climate and habitat change, the conclusion would have to be that the species Homo sapiens is simply the eventual victor in a long-running battle for ecological space among diverse hominids living in a constantly changing world.  Under conditions like these, long-term refinement would not have been the issue for our precursors; immediate exigency would have been what counted.

Homo sapiens is the only hominid species in the world today.  This clear reality intuitively favors the first scenario, in which our predecessors gamely and single-mindedly struggled toward the end-point that is us.  And as a result, paleoanthropologists have all too often tried to reconstruct hominid history by projecting our lone species far back in time, via a lineage of increasingly primitive predecessors.  But over the last few decades, as the hominid fossil record has increased by leaps and bounds, such views have become ever harder to justify.  In 1950 it was possible for the great evolutionist Ernst Mayr to argue that human phylogeny consisted of a mere three species in a single lineage.  But by 1993, my first attempt at a hominid genealogical tree already contained twelve species, spanning the past four million years.  The latest version of that tree covers seven million years and twice as many species, with as many as seven separate hominid lineages coexisting at a single point in time.  The very clear implication of this very bushy family tree is that there was no single central tendency in hominid evolution.  Rather, new variations on the hominid potential were continually thrown out to compete in the ecological arena, until one species finally emerged that somehow contrived to eliminate the competition – an event that was (very significantly) entirely unprecedented in all of hominid history.

A closer look at the details supports this broad picture, and helps us understand the complexities of how our unusual species came to be.  The earliest possible fossil hominids come from African sites between about seven and four million years old.  They make an oddly assorted group, united mainly by the claim that they moved upright when on the ground.  Terrestrial bipedality was definitively established over four million years ago, among “australopiths” that had ape-sized brains, projecting faces, and small bodies that retained excellent climbing capabilities.  This basic structure remained essentially unaltered for over two million years, although behaviorally something crucial happened with the first manufacture of stone cutting implements about 2.5 million years ago – almost certainly by an australopith.  Essentially modern body form seems to have emerged at less than two million years ago, but in the absence of any technological change.  Such change had to await the invention of the “handaxe” at some time over 1.5 million years ago, at which point taller obligate bipeds assigned to our genus Homo had already been in existence for some time.  The next major technological leap came over a million years later, when several species of the genus Homo had already come and gone.  The pattern is clear: technological and biological innovations in human evolution were both highly sporadic, and unconnected with each other.

Evolution and Who We Are Today

Our anatomically distinctive species Homo sapiens arose in Africa at about two hundred thousand years ago, but again in the absence of any evidence for significant behavioral change.  Only some one hundred thousand years later do we begin to find early indicators of the symbolic mode of cognition that today sets our species apart from all others, living and extinct.  To cut a long story short, our ability to form complex associations in the brain makes us modern Homo sapiens uniquely able to deconstruct and re-form the world around us in our minds, and to visualize alternatives.  And evidently, while the potential for this radically new cognitive mode was most likely acquired with the developmental reorganization that gave rise to our distinctive anatomy, its novel uses were discovered only significantly later.  Since the biology clearly had to be in place already before it could be used, the momentous discovery of our new potential must have been spurred by a cultural stimulus, plausibly the invention of language.  This would actually have been a routine “exaptive” evolutionary event, comparable to the tardy discovery by ancestral birds that they could use their feathers to fly.  So, purely in terms of evolutionary mechanism, there was nothing special about the emergence of our functionally altogether remarkable species.

The pattern of human evolution I have described has huge implications for the kind of creature we are.  When we single out particular human characteristics, it is easy – and tempting – to make up a story about how each one evolved, and about how each is adapted for some purpose.  But in any species huge numbers of features are inextricably bundled together, both in the genome and in the entire functioning individual.  And this makes it difficult to see how each could have been refined individually over the eons by classic processes of natural selection.  More commonly, natural selection on the individual turns out to be a stabilizing influence, while a lot of the evolutionary pattern we empirically observe reflects not individual reproductive success, but the fates of entire populations and species.  What’s more, we see few if any indications of steady progression in the human fossil record: something that is hardly surprising since we evolved over a period of notable environmental instability.  Combine such considerations with the empirical evidence of multiple hominid speciations and extinctions, and it is hard to avoid the conclusion that individual human beings can have been programmed by Nature for few if any specific behavioral function(s).

Our remarkable ability to create new realities in our minds wonderfully enables us to perceive things that lie beyond the material and the scientifically accessible.  This ability is essentially limitless; for although we are individually formed and bound by social influences of many kinds, there are no clear intrinsic restrictions on how we express our cognitive capacities.  On the plus side, this lack of constraint provides the basis for our free will.  But being unconstrained has its dangers.  And these furnish the principal reason why we should indeed care, deeply, about accurately understanding the nature of the process that produced us.  For knowing how non-directionally we evolved not only helps us comprehend why our behaviors are so frequently conflicted, contradictory, and unhelpful, it also forces us to realize the extent to which we are individually responsible for them.

Questions for Discussion:

1. Are human beings the product of long-term evolutionary trends?

2. Did technological and biological change proceed hand-in-hand in human evolution?

3. Is modern human cognition adaptive?

Discussion Summary

The argument in my essay was based on the premise that understanding the process by which Homo sapiens came into existence is crucial for understanding the kind of creature we are.  A slow process of gradual transformation and fine-tuning over the eons under the guiding hand of natural selection has profoundly different implications in this respect than the external-event-driven scenario that the bushiness of the human family tree seems to favor.

The very first comment submitted bore heavily on this issue of pattern, asking about evolutionary psychology, a field in which the fine-tuning of ancient behaviors is paramount.  Those of our behaviors today that seem to be mismatched with an expected optimum, are viewed as adaptations to an “environment of evolutionary adaptation” that no longer exists due to recent changes in human lifestyle.  However, the evidence seems to be overwhelming that, rather than having been finely honed by selection over vast periods of time, hominids in general are in fact hardy generalists.  They have been able to accommodate, especially with the aid of material culture, to a wide variety of circumstances thrown at them by changing Ice Age environments.  The evident fact that our species was eventually able to displace all of its hominid competitors in a rather short space of time is almost certainly due to its apparently rather abrupt, and recent, acquisition of its unique symbolic cognitive mode.  It is this that explains why Homo sapiens is the lone hominid in the world today, rather than one species of many.

This adventitious, non-directional history also emphasizes the extent to which we are individually responsible for our behaviors.  We cannot blame adaptation to an imagined “environment of evolutionary adaptation” for our often bizarre behaviors.  Those behaviors may, of course, be conditioned by past experience or present circumstances, but they are in essence a matter of choice.  We have not been programmed by natural selection to be a particular kind of creature, and it is this quality of free will that makes us individually answerable for our behaviors, both to ourselves and to society.

The second major thread running through commentary on my piece is the metaphysical one, bearing on the question of whether understanding our cognition, the way we apprehend and process information about the world, is actually a proper subject for science at all.  The principal commentator is certainly right to suggest that we do not understand how the brain translates into mind.  But although it is possible that we will never know (and such knowledge would indeed offer a frighteningly reductionist prospect), the question of how what we experience as our consciousness is generated has been a very valuable heuristic in driving studies of how the human brain works.  This is very much the province of science.  But, as the commentator points out, those in different fields have to be very careful about the way in which they use their words.

The nature of our awareness also came in for some comment.  There can be no doubt that, at a very basic level, all organisms are “aware.”  Even unicellular creatures distinguish between “self” and “other,” and many living things show quite complex forms of awareness, as demonstrated by their reaction to outside stimuli.  But there is nonetheless something very unusual about the peculiarly human state of awareness, the thing that we denote as our “consciousness.”  Our ability to remanufacture the world in our minds, and to react to the world as we reconstruct it, rather than as we directly experience it, seems to be qualitatively different from any other cognitive state we can observe in nature.

This ability equally gives us, and also as far as we can tell uniquely, the ability to experience the spiritual, in other words that dimension of human experience that is accessible not directly through our senses, but through our minds.  It is spiritual perception that allows human beings to conceive of themselves as “embodied spirits” that are in relation to an “infinite being.”  Such matters lie well beyond the purview of science, though our ability to conceive of them demands that we address them.  Metaphysics is only one of several fields attempting to do that.  Such endeavors are critical to the full range of human experience; and they are entirely complementary to the effort to understand the material world, rather than competitive with it.  This suggests a couple of Big Questions that it might be useful for this forum to clarify:

  1. May evolution be related in any way (or not) to the existence of an Infinite Being?
  2. Does the relationship between the Material and the Immaterial extend beyond the human mind?

19 Responses

  1. EssayReader says:

    Dr. Tattersall, you wrote: ‘Combine such considerations with the empirical evidence of multiple hominid speciations and extinctions, and it is hard to avoid the conclusion that individual human beings can have been programmed by Nature for few if any specific behavioral function(s).’ This would seem to imply that you doubt the validity of evolutionary psychology? Please elaborate on your views of human evolution and its compatibility or lack thereof with evolutionary psychology.

  2. spacecalculus says:

    Premise: Relativism

  3. David Roemer says:

    Human cognition is not the subject matter of science. It is the subject matter of metaphysics. Science addresses questions about our sense observations: Why is the sky blue? Metaphysics addresses questions about that arise because of our ability to make ourselves the subject of our own knowledge: What is knowing that the sky is blue?

    Knowing that this page is black and blue means more than that light is entering our eyes and a signal is goint to our brains. It means an awareness of this. But what is this awareness? The theory judged to be true by many philosophers is that it is a mystery, and humans are embodied spirits.

    • spacecalculus says:

      Gazing out upon the stars onto the universe, see the mystery, sui generis subject matter.

      • David Roemer says:

        A human being is indeed a unique because our knowledge of human beings comes from our transcendence, that is, our ability to rise above ourselves and make ourselves the subject of our own knowledge.  

  4. Ian Tattersall says:

    Evolutionary psychologists have certainly done a lot to clarify certain aspects of human behavior.  But the notion that humans are fine-tuned for almost anything is belied by the extraordinary variation of individual behaviors both within and among cultures.  It seems to me that if we were somehow behaviorally “adapted” to an environment that no longer exists, we might at least have some hope of identifying a human condition in the resulting behaviors.  But in practice, if there is a human condition that can be specified in terms of concrete behaviors, it is no more than a statistical abstraction.  Every behavior you can find in an individual can be matched by its antithesis in another – or even in the same person.  Perhaps cognitive dissonance is the only human universal.

     

    I would certainly agree that the origin of human awareness as we subjectively experience it is currently inaccessible to science, and will be until we understand how a mass of electrochemical signals in the brain of each of us is converted into what we experience as our consciousness.  But there is no doubt that we are descended from an ancestor that did not perceive and experience the world in the way that we do.  The transformation from the ancestral to the descendant state was a biobehavioral one, and it is certainly within the purview of science to try to establish the context within which it occurred.  Which doesn’t mean that I am not happy to leave the nature of individual experience to the metaphysicians.

    • David Roemer says:

      Is there any evidence that more knowledge about the brain will lead to an understanding of the human mind? Or is there some kind of principle that dictates rejection the metaphysical answer? If so, why should I follow this principle? Your statement that our ancestors did not “perceive” the world as we do is circular reasoning. The human mind is a myster precisely because we can’t define “consciousness.” Saying that animals did not have “consciousness” does not shed any light on the matter. We can comprehend consciousness, of course, because we have it. But we can’t explicate or explain what it is.

  5. ianful says:

    You have an excellent summary of human evolution, and I concur that humans have been around for up to seven million years. However for paleoanthropologists to generalise from a few specific remains is an error. It is possble that humans adapted to many different enviroments and the adaption that survived to today is the one that favoured using its mind and cognitive ability to modify its environment. We are now extensively adapting our environment to suit us, and that is a dead end as the earth is beginning to bite back. So modern human cognition is not adaptive.

    We have evolved as far as we can physically, cognitively, socially etc.,  so maybe we would be best heading in the direction of spiritual evolution to escape our physical bonds.

  6. Ian Tattersall says:

    The human fossil record is actually a lot better than it is often given credit for.  We now have a good sampling of hominids for at least the last four million years or so, and a fairly clear picture is beginning to emerge, of vigorous evolutionary experimentation.  It is pretty clear that the one hominid that survived up to the present did so because of its unusual cognitive system, which also gave it the ability to eliminate the competition.  This cognitive style emerged too rapidly and recently to be specifically “adapted” to anything, which is presumably why we are in such great imbalance with our environment.  A sense of spiritual identity with that environment might certainly encourage a desire to correct the imbalance; but any solutions will have to be a practical one.

     

    The problem with comparing our state of consciousness with that of any other animal is that we cannot experience any other kind of consciousness than our own.  We simply cannot know what a dog is “thinking,” or whether indeed it is experiencing anything that is meaningfully described as “thought.”  I suspect it isn’t, and that by trying to imagine what is going on in its head we just end up anthropomorphizing, which is to do the dog a clear injustice.  And it may well be correct to hazard that knowing more about the physical brain will not automatically reveal what the experiential difference is. 

    • David Roemer says:

      Ian Tattersall seems to be acknowledging another possibility: that no matter how much we know about the brain, we will never understand the human mind. In other words, the human mind is a mystery. This means there are four theories of the mind: dualism, materialism, idealism, and it is a mystery. I have put these four theories in the order of the least amount of evidence to the most amount of evidence, in my judgement. 

      • Ian Tattersall says:

        How brain translates to awareness, let alone to mind, is certainly a mystery, and likely to remain one for a very long time.  Whether it is mystery that can ever be unraveled is less certain; but meanwhile, it is a goal that keeps us moving forward!

        • David Roemer says:

          Ian’s comment indicates that he doesn’t grasp the difference between scientific questions and metaphysical questions. The question of what caused the Big Bang is a question that we can hope to answer one day. This question is not a mystery. There is no evidence that we will ever be able to answer the question of what the relationship is between the mind and the brain. This question is a metaphysical question. The question arises, not from our senses, but from our ability to make ourselves the subject of our own knowledge. 

  7. ianful says:

    It is probably better to use the term awareness as you have, rather than thought as the criterion for evolutionary progress. My investigations have led me to understand that even matter is capable of thought, so that the whole universe is thinking or aware. Even subatomic particles and photons seem to exhibit some kind of awareness in interaction with each other.  However life as we know it is capable of special kind of awareness outside itself, as plants and animals for instance interact with some awareness. We have evolved from matter through the plant world then through the animal world to the pinnacle of awareness.

  8. Ian Tattersall says:

    I am a scientist, not a metaphysician, so I am using the term “mystery” as a scientist would.  In science, something is mysterious until it isn’t.  But I do appreciate the distinction between questions that are inherently unanswerable and those that aren’t; and in the case of the brain/mind relationship it just isn’t clear from a scientific point of view which kind of question we are dealing with.  If there is doubt, though, the default for scientists is to assume answerability until it is demonstrated otherwise.  Certainly, the brain/mind relationship has been hugely important in science as a spur to research on how the brain works.

    All this of course underlines how important words are.  And I do think that there is a difference between awareness, a more or less general property of living things, and thought, which as far as we are, ahem, aware, is a peculiarly human property.  To put it another way, thought is a special case of awareness.  Awareness has certainly become more complex over the last four billion years or so, at least in our lineage; but whether or not it has reached a pinnacle in what we experience as thought is another question.  Certainly, it doesn’t seem to have been optimized for anything, certainly as evidenced by our creaky decision-making apparatus!

     

    • David Roemer says:

      If the mind-body problem is unanswerable, then humans are embodied spirits and finite beings. This means an infinite being exists, which means we have to decide whether there is life after death. For this reason, it shows poor judgment, in my opinion, to speculate about the possiblity that the mind-body problem will be solved some day.

  9. Ian Tattersall says:

    The mind-body question is usually posed in philosophical terms, while the specific issue of how electrochemical activity in a complexly-structured brain is related to what we experience as our consciousness is a proper focus of scientific investigation.  This makes the latter unlike the issue of the existence of life after death, which is not  directly accesible to science — although people’s beliefs about it, and their experiences related to those beliefs, may be.   Individual human beings are, alas, all too finite; but from the standpoint of science it is not entirely clear how our own existence directly implies that of an infinite being.  We are able to conceive of all kinds of things that may not be perceived by our senses, and gazing on the stars unquestionably generates awe; but whether or not our concepts of the immaterial correspond to anything beyond our own constructs is beyond the remit of science, which is limited to the observable.  

  10. Ian Tattersall says:

    Well put.  A key element of human cognitive uniqueness is the ability to stand back from oneself, as it were, and to view oneself from the exterior.  This doesn’t, of course, make us necessarily objective!  But it does make it possible for us to believe that we are accessing the truth.  If the resulting formulations are testable in terms of what we can observe about ourselves and the rest of nature — or are closely consistent with what we know that is testable — then they fall within the realm of science.  If they are not, then they pertain to other, separate, domains of human knowledge.