Lifeboat Foundation

Part 1: 10,000 years      Part 2: 100,000 years       Part 3: a million years    Part 4: ten million years

Ten million years ago, things were very different. It is thought that our ancestors of that time, roughly 400,000 generations ago, were hominids (Latin: Hominidae) who had not yet branched out into their current descendant — orangutans, gorillas, bonobos, chimpanzees — and us. The hominid family and our genus, Homo, are well-known, landmark taxa in our evolutionary tree. However there are also superfamily, subfamily and other auxiliary taxa that are instructive (or maybe just confusing!) to mention.

The hominid family forms a branch of the hominoid superfamily, which also includes gibbons. The hominids branch in turn into orangutans and the hominine subfamily (last syllabus pronounced like the word “nines”). The hominines branch into gorillas and the hominin (no “e”) tribe, which in turn branches into chimpanzees and bonobos, on the one hand, and the hominan (with an “a”) subtribe on the other, of which we are the only surviving example. The hominans contain the genus Homo, or humans. This terminological mess of hominthises and hominthats may seem ridiculous! And maybe it is. However, one way to help remember the ordering is to keep in mind that the homin– terms are — almost — in alphabetical order from smallest to largest grouping: hominan, hominin, hominine, hominid, hominoid, with 1 exception. Hominid is out of order but at least next to the other d-containing name, hominoid.

Some milestones of prehistory. About 75 million years ago, primates split off from the rest of the evolutionary tree of life, or the Linnaean taxonomy, after Carl Linnaeus (1707−1778), the Swedish scientist who created this branching map of evolutionary relationships that bears his name and is still with us today. 75 million years is a fairly long time ago, even for biological evolution; our roots go deep! Apes diverged from the monkeys about 32 million years ago. Apes were the first “hom-,” the hominoids. The great apes, technically the hominids, came along around 19 million years ago. They include orangutans, gorillas, chimpanzees, bonobos, and humans. Moving into the upper reaches of the 1 – 10 million year ago time scale, a likely common ancestor race of all living hominines, from gorillas to us, but not orangutans since they had already branched off, was the Nakalipithecus. A partial fossil was found near Nakali, Kenya. This hominine is just under 10 million years old.

Gorillas then split off around 7 million years ago. Chimps and bonobos split from our common ancestral species roughly 5 or 6 million years ago. That species enjoyed considerable success in its day, spawning almost 2 dozen separate identifiable human-like hominins. Most are somewhat obscure, though our earlier-mentioned friends neanderthalensis, habilis and ergaster are among them. Although only 1 strain survives today, us, this remarkable species has pretty much achieved world domination. The jury is still out on its fitness to rule but the question will certainly be resolved sooner or later. Perhaps you are reluctant to call such extinct species as Homo habilis (Latin for “handy man”) and Homo ergaster (“working man”) human. If so, recall well-known hominid Groucho Marx, who famously opined, ” I don’t want to belong to any club that will accept me as a member.”

The dramatic changes over the past 10 million years will most likely be mirrored in the next 10 million. But how? There are many ways, but let us focus on brain size and intelligence.

Humans may be characterized as big headed, and we’re proud of that. Our brains are big, bigger than all but a few very large animals, elephants and whales in particular. But we are way ahead of even those animals on other crucial brain measurements. Since the brain mass of a species tends to increase with species body size, but not as fast, a measure called encephalization quotient is often used to express the deviation of brain size from what would be expected for a given body size if the organism had an average encephalization quotient of 1.0. On that metric, human brains are over 7x bigger than expected for an organism of our size. No other animal is that high. One survey puts elephants and whales at 1.3x and 1.8x respectively. Bottlenose dophins get to a little over 5x, and their brains are in fact close in size to ours, possibly making them geniuses of the animal kingdom. White-fronted capuchin monkeys get to almost 5x although absolute brain size is a lot less than for humans because their body size is so much smaller. By contrast, cats are 1x, while dogs are 1.2x. The lowly and somewhat homely opossum, at a mere 0.2x, might thus be characterized as better endowed with beauty than brains.

Even ignoring body size entirely, we are still way ahead on the number of neurons in our brains. Those big animals with brains bigger than ours actually have fewer neurons, the information processing units of the brain. By analogy, ordinary computers are getting more powerful year by year not because they are getting bigger but bcause their processors are being made with more information processing units (which for computers are not neurons but transistors). These transistors are actually getting smaller over time. Thus computers, as they get more powerful, are actually getting smaller, not bigger.

A dramatic process of brain enlargement in our past began approximately two million years ago. Our brains have literally tripled in size since that time. Presumably, that is why some primates like bananas, while some of us like books in addition to bananas. What if this process continued? Will our brains triple again over the next couple million years, giving us descendants who chuckle condescendingly at our admiration for mere books as we might chuckle over a monkey’s admiration for mere bananas? Would such brainy descendants find the solutions to our most vexing problems of war and peace, poverty and excess, illness and health, love and hate obvious and easily taught in elementary school? Perhaps they will, but there are serious limits such rapid brain growth. These limits appear to forbid brain size (measured as number of neurons) from increasing at a rapid clip forever. Specifically, another tripling would, it appears, rqeuire major changes in brain structure surpassing the structural differences between human brains and those of other apes — in short, a major evolutionary leap requiring significantly more than a measly few million years. On the other hand, doubling brain size can be done more easily (and presumably quickly) because no major architectural changes would be necessary. Thus, our brains can fairly easily double, but tripling would be more problematic.

Here is a mathematical explanation of why. First, the brain is composed of many chunks which must communicate with each other. In contrast, the old syncytium theory that the brain is essentially a big blob of weakly organized tissue, sort of like a big ball of cotton, had been largely disproved by Spanish neuroscientist Ramon y Cajal by 1900, a feat for which he won the Nobel prize in 1906. The bigger the brain, the more chunks there are that need to communicate. The more communicating chunks, the more neurons need to be devoted to communication (thus acting like the telephone wires and internet cables of the brain). Let’s see why this is a problem.

Suppose 3 chunks, 3 people, 3 computers, 3 offices, or 3 of any kind of communicating entity all need to communicate with each other. How many communications paths are needed? Three: one between A and B, one between B and C, and one between A and C. Suppose we add a 4th communicator, D, that needs to communicate with all the others. How many more, new paths are needed for all to communicate? Four minus one, or three: between D & A, D & B, and D & C. We added one more communicating chunk and needed to double the communication paths. The problem just gets worse the more chunks we add: the thousandth chunk requires adding 999 new communication paths, running between the new chunk and each of the previous 999. The fourth chunk needed 3 more paths but the thousandth needed 999! Thus adding one new chunk to a large brain that already has lots of chunks requires lots of extra neural tissue to be added for communication purposes. In practice, this is the white matter of the human brain cortex which, because of this problem, forms a disproportionate fraction of the human brain compared to other primates. It gets progressively more biologicallly expensive to incrementally increase brain capacity and humans are in the zone where this expense starts to become prohibitive of dramatic increases.

Of course, only doubling our brains is nothing to sniff at and could lead to impressively brilliant descendants, even if much more than doubling proves unachievable. We can only hope that such high-flying beings can still smell the flowers and, indeed, enjoy an occasional banana.

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