The interesting question is what caused these rapid increases in brain size, driving hominin intelligence from the chimpanzee-like capabilities of Australopithecus to modern humans in only a few million years. Again, this is a very active area of research, and there are differences of opinion amongst experts. This is the nature of science at the frontier of knowledge, and this is what makes science exciting and successful. The model we are focusing on is the most widely accepted theory of human evolution. It is known as the recent single origin hypothesis, or more colloquially the ‘Out of Africa’ model, and the dates and locations we have described so far might be referred to as ‘textbook’. There is broad consensus, therefore, about the ‘When?’ and the ‘Where?’ But not ‘Why?’, and it is to ‘Why?’ that we now turn.
There is a trend towards larger brain size over the 4 million years since the emergence of Australopithecus, but the trend is not gradual. There is a large jump around 1.8 million years ago with the emergence of Homo erectus, and another jump just under 1 million years ago with Homo heidelbergensis. The final jump occurs when Homo sapiens emerges 200,000 years ago. The time period around 1.8 million years ago also corresponds to a leap in the number of hominin species present in the Rift Valley; there were at least five or six species living side by side, suggesting that something interesting occurred around this time which may have been responsible for, or was a contributing factor to, the observed increase in brain size, particularly in Homo erectus.
* * *
CRANIAL CAPACITY
The internal volume of the primate skull increases from 275–500cc in chimpanzees to 1130–1260cc in modern humans. Neanderthals had a brain capacity in the range 1500–1800cc – the largest of any hominids. Recent research indicates that, in primates, whole brain size is a better measure of cognitive abilities.
* * *
The large number of deep-water lakes appearing temporarily in the Rift Valley around 1.8 million years ago indicates that at this time the climate, and in particular the level of rainfall, was varying quickly and violently. Similar climate variation occurs around 1 million years ago and 200,000 years ago, and this appears to be correlated with increase in hominin brain size. The theory is that rapidly changing climatic conditions in the Rift Valley at these specific times played an important role in driving the increases in brain size.
The selection pressures that may have led to these increases are unclear. Selection for adaptability was probably an important factor, but social factors such as the ability to live in large groups, and intra-species competition as a result of the larger number of species living side by side, particularly around 1.8 million years ago, must also have played a role. Having said that, it does appear that climate variation in the Rift Valley 1.8 million, 1 million and 200,000 years ago could have been a contributing factor to the development of our intelligence. This is known as the Pulse Climate Variability hypothesis.
We can now bring all these threads together to reveal a surprising and, for me, dizzying hypothesis which, if correct, sheds new light on the immensely contingent nature of the existence of our modern civilisation – or, in simpler language, why we are bloody lucky to be here!
The three dates – 1.8 million, 1 million and 200,000 years ago – correspond to the times when the Earth’s orbit was at its most elliptical. As described above, the mechanism by which climate changes due to precession at these times is well understood. The Pulse Climate Variability hypothesis asserts that the unique geology and position of the Great Rift Valley amplified these changes, and that early hominins responded by increasing their brain size. If this is correct, our brains evolved as a response to changes in the Earth’s orbit, driven by the precise arrangement of the orbits of the other planets around the Sun, and precession, driven primarily by the gravitational interaction between the Moon and Earth’s axial tilt, both of which date back to a collision early in the history of the solar system, and all this is plainly blind luck. Without an inconceivably unlikely set of coincidences, and the way these conspired together to change the climate in one system of valleys in wonderful Ethiopia, we wouldn’t exist.
* * *
CRANIOFACIAL DEVELOPMENT
Homo neanderthalensis has a unique combination of features on its skull that is distinct from fossil and extant ‘anatomically modern’ humans. Modern research involving morphological evidence, direct isotopic dates and fossil mitochondrial DNA from three Neanderthals indicates that the Neanderthals were a separate evolutionary lineage for at least 500,000 years. However, it is unknown when and how Neanderthals’ unique craniofacial features emerged.
* * *
If this is correct, then what a response! I held a brain for the cameras at St Paul’s teaching hospital in Addis. It is the most complex single object in the known universe, a most intricate example of emergent complexity assembled over 4 billion years by natural selection operating within the constraints placed upon it by the laws of physics and the particular biochemistry of life on Earth.
The brain contains around 85 billion individual neurons, which is of the same order as the number of stars in an average galaxy. But that doesn’t begin to describe its complexity. Each neuron is thought to make between 10,000 and 100,000 connections to other neurons, making the brain a computer way beyond anything our current technology can simulate. When we do manage to simulate one, I have no doubt that sentience will emerge; consciousness is not magic, it is an emergent property consistent with the known laws of nature. But that doesn’t lessen the wonder one iota. Out of this evolutionary marvel, we emerge. Thoughts, feelings, hopes and dreams exist on Earth because of electrical activity inside a 1.5-kilogram blob of stuff, which hasn’t changed much since the earliest modern humans began the long journey out of Africa.
If you could travel back in time and bring a newborn baby from 200,000 years ago into the twenty-first century, allowing it to grow up in our modern society with a modern education, it could achieve anything a modern child could. It could even become an astronaut. Which sets up one more question: if the hardware was present 200,000 years ago, then what changed to lift us from the Great Rift Valley into space?
‘AN UNPRECEDENTED DUEL WITH NATURE’
‘The best thing we can do now is just to listen and hope’, said Cliff Michelmore, broadcasting from the BBC’s studios 24 minutes from the expected splashdown of Apollo 13. On 17 April 1970, I was too young to watch the live broadcast, but I’ve seen the recording many times since. Grainy pictures from the deck of the USS Iwo Jima, its flight deck crammed with nervous sailors off the coast of Samoa; Patrick Moore and Geoffery Pardoe grim-faced in the studios, and James Burke, famously, with fingers crossed behind his back. ‘Apollo control, Houston, we’ve just had loss of signal from Honeysuckle’. Honeysuckle Creek Tracking Station in Canberra, Australia, was the last ground station to contact Apollo 13 before it entered the Earth’s atmosphere on its way home. Signal loss during re-entry is routine high drama on all space missions; the ionisation of the atmosphere caused by the frictional heating of the spacecraft blocks radio signals, typically resulting in radio silence for four minutes. On Apollo 13, six minutes passed in silence. The brilliance of the BBC’s quartet of commentators was in the silence they allowed on the airwaves. The only sound was the static of the NASA feed – a moment of genuine tension. No need for vacuous media babble; nobody could bring themselves to speak. ‘We’ll only know whether that heat shield was damaged by that explosion three days ago when they come out of radio blackout in just over two minutes’ said Burke. Silence. As four minutes passed, Houston reports ‘10 seconds to end of radio blackout’. Silence. Houston: ‘We’ve had a report that Orion 4 aircraft has acquisition of signal.’ ‘They’re through’ says Burke. ‘Let’s not anticipate, because the parachutes may have been damaged.’ ‘Shutes should be out’, murmurs Burke; not broadcasting, just saying. ‘There they are, there they are!’ ‘They’ve made it’ remarks Moore. And then applause. ‘I make it no more than 5 seconds late!’ shou
ts Burke, ‘No more than 5 seconds late!’
The safe return of Apollo 13 was arguably NASA’s finest hour; 55 hours 54 minutes and 53 seconds into the mission, 320,000 kilometres from Earth, Lunar Module pilot Jack Swigert switched on a system of stirring fans in the hydrogen and oxygen tanks in the service module, a routine procedure. A piece of Teflon insulation inside the tank had been damaged, it was later discovered, by a series of unlikely events that happened on the ground during the preparation of the spacecraft for flight. The wire shorted, the tank exploded, and the side of the service module was blown off, critically damaging the spacecraft’s power supply systems and venting the crew’s oxygen supply out into space.
The Command Module, the only part of the spacecraft capable of surviving a re-entry through the Earth’s atmosphere, was now running on batteries and with a rapidly diminishing oxygen supply that would not keep the astronauts alive long enough to return to Earth. The only option was to shut down the Command Module and retreat to the Lunar Module, effectively using it as a life raft. Lovell later spoke of how he didn’t regret the mission at all. He was robbed of his Moon landing, which must have been doubly frustrating given he’d already flown to the Moon on the historic Apollo 8 mission. But his reaction, revealed in interviews in later life, offers great insight into the character of a test pilot. ‘We were given the situation,’ Lovell explained, ‘to really exercise our skills, and our talents to take a situation which was almost certainly catastrophic, and come home safely. That’s why I thought that 13, of all the flights – including [Apollo] 11 – that 13 exemplified a real test pilot’s flight.’ Both Lovell and Haise have said that the idea of not returning safely to Earth never really came up. ‘There was nothing there that said irrefutably we don’t have a chance.’
Haise was correct, of course, because they did return safely. But they only had enough food and water to sustain two people for a day and a half and had to improvise a carbon dioxide filter to provide them with enough breathable air for the return journey. Locked in the Lunar Module with limited supplies of food and water and temperatures dropping towards freezing, life was far from comfortable. With the Command Module powered down to preserve the sparse battery supplies left after the loss of the fuel cells, the crew had to survive in a hostile environment with limited resources. Like so many outposts of human civilisation throughout history, shortage of water was a primary concern. Water was critical on the Lunar Module for two reasons; as well as being needed to keep the crew hydrated and to rehydrate the food, it also cooled the electrical systems on the spacecraft. Conserving water therefore became a critical part of the plan to return to Earth. Reducing their intake to just one-fifth of a normal human water ration, each of the crew suffered severe dehydration and together they lost 31.5 pounds in weight – nearly fifty per cent more than any other Apollo crew.
Despite the discomfort, setting a new mission trajectory and navigating their way along it remained the primary challenge. The standard way to make in-flight course corrections on Apollo was to use the Command Module’s main engine, but the system was located close to the damaged site and mission controllers decided that lighting it was too great a risk. Instead, the decision was made to use the LM’s descent engine to send them around the far side of the Moon and back to Earth in four and a half days. This is known as a free-return trajectory – a slingshot around the Moon at the correct angle to return directly to Earth. No one knew if an engine designed for a completely different purpose would perform this function successfully – but they knew that if it failed they would not return.
Five hours after the initial explosion, the LM engine was fired for a 35-second burn, successfully putting the crew onto a free-return trajectory. This solved one problem but raised another. Calculations of the trajectory estimated return to Earth 153 hours after launch, which would push the key reserves on the craft too low for comfort, so it was decided to speed up the spacecraft with another burn, cutting the total time of the voyage by ten crucial hours. Such were the slim margins on Apollo 13. The main navigation system in the Command Module was out of action, so Lovell had to calculate the correct navigational inputs, while back at base, mission control worked through the same calculations as a cross-check. Lovell also got to use his sextant, which he played with on Apollo 8, to navigate by the stars for real.
The calculations are preserved as handwritten notes, in the Lunar Module System’s Activation Checklist. This was the checklist Lovell and Haise would have used to fly down to the Moon’s surface. Now useless, Lovell used the waste paper to write down instructions to put the ship on course for Earth. Two hours after they rounded the far side of the Moon, the LM engine fired, following Lovell’s handwritten checklist, increasing the speed of the spacecraft by 860 feet per second and buying them ten precious hours.
The most dramatic rescue in the history of human spaceflight stands as a testament to the brilliance of the three test pilots Lovell, Haise and Swigert, and also to the brilliance of the engineers on the ground who simply knew their stuff. NASA’s Apollo engineers were young by today’s standards; the average age of the team in mission control for the splashdown of Apollo 11 was 28 years old. This is one of the reasons why the United States reaped such a colossal economic reward from its investment in Apollo. The generation of scientists and engineers who worked on and were inspired by Apollo went out into the wider economy and delivered a huge investment return; a series of studies, including one by Chase Econometrics, showed that for every dollar invested in Apollo, at least $6 or $7 was returned as increased GDP growth. This should, of course, be bloody obvious – new knowledge grows GDP – but every generation of politicians seems to require re-educating to understand the difference between spending and investment. And while I’m polemicising, let me say that the usual political argument – that public support is needed for such large investments – is drivel. Firstly, the investment in NASA wasn’t that large, never exceeding 4.5 per cent of the Federal budget throughout the lifetime of Apollo. And secondly, it is a politician’s job to lead from the front. Make the case that investment in knowledge, in pushing the boundaries of human capabilities and exploring all frontiers, both physical and intellectual, is the key to the future wealth, prosperity and security of civilisation. Aspire to be Kennedy, not a hand-wringing apologist for intellectual and technological decline.
The nine Apollo flights to the Moon remain the furthest modern humans have explored beyond the Rift Valley in our 200,000-year history. Homo sapiens first left Africa in large numbers 60,000 years ago, so on geological timescales we didn’t hang around. Our ancestors followed waves of earlier hominins. Homo erectus were in South East Asia 1.6 million years ago, and half a million years later Neanderthals had colonised Europe and Homo floresiensis were in Southern Asia. The details of the migration 60,000 years ago are particularly well understood as a result of the combination of genetic, archaeological and linguistic studies. The precision comes in part from the tracking sequences of mitochondrial DNA, which is passed down from the mother and not shuffled by sex. This makes it relatively stable and easy to track – changes are caused by mutations alone. The most widely accepted interpretation of the data suggests that a small population of between 1000 and 2500 individuals left East Africa 60,000 years ago and moved north across the Red Sea and through Arabia. The group then split, moving into Southern Europe 43,000 years ago, and travelling through India and into Australia on roughly the same timescale. The crossing into North America, via eastern Russia, was probably later, around 15,000 years ago.
* * *
OUT OF AFRICA
Evidence from fossils, ancient artefacts and genetic analyses combine to tell a compelling story of the migration of anatomically modern humans. Two possible routes have been identified for the human exodus out of Africa. A northern route would have taken our ancestors from their base in eastern sub-Saharan Africa across the Sahara desert, then through Sinai and into the Levant. An alternative southern route may have charted a path
from Djibouti or Eritrea in the Horn of Africa across the Bab el-Mandeb strait and into Yemen and around the Arabian Peninsula.
* * *
These early groups of humans were hunter-gatherers. It has been estimated that the basic social units would have reached a maximum of around 150 individuals. This is known as Dunbar’s number, after the British anthropologist Robin Dunbar, who suggests that the largest social group amongst any given population of primates is related to the size of their brains (specifically the neocortex). Dunbar’s number can be observed today in the size of the average person’s social network, both in the real world and online; our hardware – the brain – has not changed appreciably since the first humans appeared in Africa 200,000 years ago. These social groups would have lived in loosely bound tribes, perhaps reaching a size of between one and two thousand individuals, operating within an area of around 100 kilometres. Populations would stabilise, perhaps in response to social factors, but also as a result of increased mortality rates caused by parasitic diseases and diminishing per-capita resource availability, before fragmenting and spreading. In this fashion, the rate of progression of our ancestors across the globe has been estimated to have been around 0.5 kilometres per year, or 15 kilometres per generation. Population density did not rise significantly beyond these levels until these proto-societies shifted from a hunter-gatherer lifestyle to agriculture around 12,000 years ago. This shift was the trigger for the development of civilisation: the most important single step, following the migration out of Africa, in the journey from apeman to spaceman.
Human Universe Page 14