They say modern humans appeared about 300 thousand years ago. I understand why we say it this way, and it sort of makes sense, but I don't fully understand what it must have been like. I was taught when first studying biology that most everything is a species, and each species is defined mostly by the fact that it can only viably reproduce with itself. This gives you a handy tool to decide if those two finches that look similar are actually the same species, if they can make a non-sterile offspring, then they are probably the same species. The classic example of something which violates this rule is the offspring of a horse and a donkey, a mule, which is sterile and therefore not either it's own thing, nor proof that horses and donkeys are the same species.
As you start to learn more about animals and evolution and things it becomes pretty obvious that this definition is sort of a hazy rule of thumb that only applies sometimes and is actually only useful for broad layman's explanations. Sometimes what seems like two separate species can break this rule and interbreed, which makes one wonder if they aren't actually just a subspecies, maybe not-so-distant relatives? So you examine it a bit further and try to come up with a new more precise and accurate way of defining a species. After all, a bird and a bear are sufficiently different to not really need this definition at all, it's the brown bear and black bear that benefit from such labels.
Quickly the question of what makes one bear "brown" and one "black" turns into an arbitrary line we drawn in the proverbial sand. It doesn't matter at all to animals in nature, or to nature itself, but it's common to forget that. It's easy to imagine biology as a branching tree of life as it so often is presented. Zooming into this tree where two species might diverge, right at the fork between two of Darwins finches reveals the shortcomings of the metaphor. It's not really true that those birds at one point changed into new species, nor can it really be defined as a gradual progression from one to another. It's a collective, ongoing continuum of individuals which can at best only be reduced to the myriad of possible genetic combinations that more or less define them. Although even genetic studies, the hopeful bottom line objective measure for biologists, are riddled with exceptions and unexplained mysteries which confound and resist all categorization.
We need to think about humans in this way more. Laypeople probably imagine human evolution in the way the archetypal diagram tends to show, with a line of humanoids slowing standing up straight, shedding hair and snouts, and eventually appearing as John the hairy businessman you saw on the street yesterday. This is not just a gross simplification, it's strictly inaccurate mostly in that it derives the path of human evolution as a linear progression, more or less, with stylistic liberties withstanding. This is not a fair explanation. If you had to make even one small adjustment, you would need to at least incorporate the branching tree model to begin to include the dead ends of Hominins and the forking grapevines of specimens which have been discovered but not necessarily placed correctly.
What's most fascinating about the true recent evolution of our ancestors is that, as best we can tell from the scattered bones and carbon dating techniques, Hominins have been an ocean of morphology, genetic makeup, and archaeological evidence for hundreds of thousands of years. Every year we find more and more evidence that humans today have genetic remnants of what we say are non-sapien ancestors, the neanderthals, the vaguely defined denisovans, and others still locked up in our DNA. We find ever more fragments of bones and skulls in various layers of sediments all over the world which are related to humans in shape or size, and we try to ultimately quantify how different these bones are from what we might find.
If you exhumed a modern graveyard, to find the remains of human beings all having lived in the last 200 years, you might find a reasonable range of differences in the shapes of skulls and teeth and bones each marked with the unique evidence of that individuals life. If you could assess and sort all the bones of every living and dead person on earth today, you would find wild exceptions and heaps of similarities, forming an indescribable ocean of variation without singular cause.
In contrast, the bones we have managed to unearth in israel Olduvai, heidelberg, and other sacred and hallowed sites which belonged to individuals dating as far back as 7 million to a merely several hundred thousand years ago make up a few glimmers of evidence among a virtual infinity of individuals. These specimens are almost never complete, and their age and location are always subject somewhat to debate. Lucy, a shining star even among these lucky individuals chosen by time to represent their species, is an incomplete skeleton. Even if she were a completely preserved skeleton down to the ear bones, the sheer among of time endured will warp the appearance, the absence of all soft tissues obscures the true nature of Lucy, and so many other factors prevent our knowing the truth of her existence. This goes without saying for fossils, it seems obvious, but it's important to remember that the conclusions we draw about human evolution are made from woefully undersampled data. Imagine that only 5 modern homo sapiens were selected to represent the diversity of all others, and then they were stripped of their physical possessions, immediate environment, all flesh and blood and a good portion even of their bones. Then they are asked to provide insight into the behavior of all others of their kind, from the short lived to the diseased, the rich as well as the poor. It is on this amount of information, usually much less that we derive the million year long ladder of human evolution that we hope will teach us more about ourselves and explain where we came from.
The synecdoche that is Lucy or an errant jaw bone unearthed in the Olduvai Gorge is both humbling and astounding, but it is also misleading. As much insight as we can gain from a post-mortem assessment of a fractured fossil skeleton, it can never come close to explaining broader questions of behavior, and the admittedly more impossible questions of individual experience. Modern anthropology has infinitely more to learn from humans alive today, or even alive yesterday, than an archaeologist could ever hope to derive from mere bones. We pretend, as we love to in science and history, that we have some idea, however limited, of what was going on back then when direct observation was impossible. From this we expound an image of time, evolution, and biology that is based on this imagined and changing set of observations which cannot possibly exist, it's a very abstract idea. The first impossibility is the large number of individuals, trillions of living things which have existed never to be known of again, and the fact that the few individuals we have evidence of are small incomplete statistical anomalies without much of a reference point. The second impossibility is the idea that 7 million years can be known. We try to know it with analogy, by dating rocks and molecular clocks. We can observe that two dots of light churned up in different
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