Big Brains

There’s probably no single event more significant in the history of human evolution than the harnessing of fire. Many species make and use tools, but only humans control fire. Fire provided early humans a means to protect themselves from predators. Fire provided humans with warmth and light, and expanded productivity into the night. Socializing around a campfire may have been an essential part of human development.
   Perhaps the biggest benefit of fire was for cooking. Cooking food provided better nutrition and made food safer to eat. Cooked meat was easier to digest because less energy was spent digesting the tougher proteins and connective tissues.
   Cooking plants that contained starches made the complex carbohydrates they contained more digestible so that more energy could be absorbed from them. The human digestive system has evolved after we started eating cooked foods: our teeth, jaws and digestive tract have all gotten smaller, allowing our developing brain to have a greater share of the food energy taken in. Eating cooked food helped provide the extra energy required to support a hunter-gatherer lifestyle.
   The earliest known evidence for the controlled use of fire comes in the form of ash and charred bone excavated from a South African cave that is known from previous digs to have been occupied by early man. These materials were found alongside stone tools in a layer dating back about a million years.
   Although modern humans are the only human species alive today, originating about 200,000 years ago, other human species once roamed the Earth, such as Homo erectus, which arose about 1.9 million years ago.
   Some anthropologists think that Homo erectus was cooking as far back as 1.9 million years ago and was the reason that they experienced major brain expansion at that time. Others think that brains got bigger just by the introduction of meat into their diets and that while there was the opportunistic use of natural fire, it was not until about 300,000 to 400,000 years ago that early humans fully mastered the use of fire.
   One thing is certain—our brains have tripled in size over that last two million years. But evolution doesn’t say anything about whether larger brains are good or bad, just that it happened. Author Kurt Vonnegut believes that our brains have over-evolved: “Our brains are much too large. We are much too busy. Our brains have proved to be terribly destructive.”
   Vonnegut explored this theory in his 1985 book Galapagos where our big brains have brought civilization to the brink of destruction. The last humans ironically survive because they get stranded and isolated on the Galapagos Islands made famous by Charles Darwin. They spend the next million years de-evolving.
   As evidence for his theory, Vonnegut says that big brains invented nuclear weapons and the Third Reich. Even Einstein noted that “He who joyfully marches to music rank and file, has already earned my contempt. He has been given a large brain by mistake, since for him the spinal cord would surely suffice,” indicating his belief that war is a huge step backwards in human evolution. And while I’m more optimistic, I didn’t witness the bombing of Dresden firsthand as did Vonnegut, nor did I have to flee my home and country out of fear for my life as did Einstein. Food for thought…

The Evolution of Sight

The compound eye of the Arctic krill is highly evolved
for such a small creature.

Our vision is based upon a very small sliver of the electromagnetic (EM) spectrum. Humans can sense EM radiation between the wave lengths of 380 nm and 750 nm, ranging from violet through red. We cannot see, however, all the electromagnetic chatter that is happening around us outside the visible range. We’re bathed in an ocean of electromagnetic waves all day, every day. There is nothing qualitatively different about the visible portion of the spectrum compared to radio waves or ultraviolet waves, for example; it’s just that we can sense some waves (which we call light), yet have no awareness outside this narrow range.
   There’s a very good reason for this—it’s not just a coincidence. It’s because of the way light attenuates in water. Attenuation is the physical property that describes the gradual decrease in intensity of electromagnetic radiation as it travels through a medium—in this case sea water. When the Sun’s rays reaches the surface of the ocean, visible light is absorbed at the longest wavelengths, red and orange, first. Blue and violet wavelengths reach deeper into the water column, which is why deep-ocean water appears blue.

The attenuation (decibels/meter) of EM radiation in water as a function of wavelength (nm). EM attenuation in water drops six orders of magnitude just around the visual range.

   Now expand this concept to the entire spectrum of EM radiation. Species began to evolve eyes during the Cambrian explosion (about 540 million years ago), while life was still confined to the sea. Eyes developed sensitivity to the 380-750 nm range because that band of EM radiation travels through water with an attenuation 1,000 orders of magnitude lower than that of adjacent wavelengths. Being able to see in deeper water provided an evolutionary advantage, so the earliest animals developed sensitivity in the portion of the spectrum that reached the greatest depth. During this time the eye developed rapidly. After creatures began to move onto land, there was no evolutionary incentive to see a larger portion of the spectrum because every other organism also saw in this range.

A Trilobite fossil with the eye structure outlined in red.

   Sight gave predators the ability to find prey, triggering an evolutionary arms race where animals either evolved or died. Trilobites possessed highly-advanced compound eyes that gave them a competitive advantage in both finding food and avoiding predators. It’s no surprise that trilobites thrived during the Cambrian explosion to become one of the most diverse and successful classes of all the early animals, roaming the oceans of the world for the next 270 million years. Continual adaptation during the Cambrian explosion was needed in order to maintain relative fitness amongst all the other species that were evolving at the same time. This is known as the Red Queen Effect, a term taken from Lewis Carroll’s Through the Looking-Glass where Alice and the Red Queen are running yet not getting anywhere: 

   “Well, in our country,” said Alice, still panting a little, “you’d generally get to somewhere else—if you run very fast for a long time, as we’ve been doing.”
   “A slow sort of country!” said the Queen. “Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!”

The Neanderthal Genome Project

The majority of the DNA used for the Neanderthal
Genome Project was obtained from the bone fragments
of three females who were excavated from the Vindija
Cave in Croatia. Image: Max Plank Institute for
Evolutionary Anthropology/Frank Vinken.

Found in Europe and parts of Asia, Neanderthal lived from about 400,000 years ago until 30,000 years ago. Neanderthals were comparable in size to Homo sapien, but more robust. They also had similar brain sizes, but their skulls were shaped differently. Researchers have long wondered why Neanderthal went extinct. Some think the lack of genetic diversity made it too hard to persevere through plagues while others think that their smaller, less sophisticated social groups played a part in their demise. We do know that their stronger build would have required more food which would have been a disadvantage during hard times.

   In 2010, scientists from the Max Plank Institute for Evolutionary Anthropology in Germany reported that they had completed a first draft of the Neanderthal genome. This research was based on analysis of four billion DNA base pairs. Through DNA analysis, we have learned insights that had been previously unknown through only fossil evidence. Their study suggests Neanderthals had an effective population smaller than that of modern humans, and lived in small, isolated groups. And although we share about 99.7% of the same DNA, only 1-4% of modern non-African humans have inherited DNA from Neanderthals, and Africans have no common lineage. Most likely, the interbreeding occurred early in the migration of humans out of Africa.

   DNA analysis has also proven fruitful in a recent discovery in a cave in Northern Spain. Researchers there found the butchered remains of an extended Neanderthal family that were killed and eaten by other Neanderthals. The bones were cracked open by stone tools for marrow, suggesting that they were cannibalized before the cave collapsed and buried their remains. Researchers found that the group was genetically very similar, confirming that Neanderthals had less genetic diversity than modern humans. They also discovered through DNA analysis that they lived in small groups of males that were closely related, and that the females came from other tribes, a social system called patrilocality. Clearly, our understanding of human evolution is benefitting greatly from DNA analysis.