lecture 8 - evolution of a cognitive brain Flashcards
evolution and our family tree
diagrams in notes
veterbrate brains … function well in lots of arrangements
branches not ladders - branchinh bush in Darwins sketch
Species change over time - evolution
Darwin preferred the phrase ‘descent with modification’, because of the misleading implication that ‘evolution’ entails progress (towards maturity or advanced states).
Species change over time.
But not all species change a lot. Some are highly successful and stay almost the same for millions of years (e.g. sharks)
Why do some change a lot?…. Because their environment either changes, or is more competitive (or both).
How do species change? ‘natural selection
“survival of the fittest” mechanism by which change is driven – what kind of fitness?
Fit to the environment….and environments change
Darwin was inspired by artificial selection…what farmers do when breeding livestock
(the farm and farmer is the ‘environment’ for livestock; the individuals that best fit the farm, e.g. by producing more milk or being more docile, get to breed most).
there is no measure of what is best is what the environment wants - Darwin thinks can apply this to whole natural world
eg how does resistance evolve - when the environment changes creates pressure and drives natural selection. new generation has insecticide resistance.
the Black Death (14th century) seems to have changed the proportion of gene-variants in European populations
evidence for this in humans - genetic evidence eg from skeletons from 14th century Black Death
One gene-variant seems to have given people 40% better chance of surviving
(it codes for a protein that is good at chopping up invading microbes).
There was a 10% shift in its prevalence over 2-3 generations, and it remains more common today than before the black death.
Relative advantage depends on the current environment – today that same gene-variant is associated with higher risk of auto-immune diseases.
what’s positive in one enviormet can be negative in another environment
Natural selection (key concepts)
Natural selection simply means that those individuals with most surviving offspring have a stronger genetic influence on the next generations
KEY ingredients:
1. variation – individuals differ in genetics (otherwise next generation will be the same no matter what)
2. competition – number and success of offspring varies (so that the genes from some individuals are more represented in the next generations). not all genetics have same probability of making it to next generation
Key contributors to having successful offspring:
Survival
Sex: do you create offspring?
Ensuring (some of) your offspring survive
Giving your offspring a competitive advantage…
(for animals living in groups, things that influence variance in survival, sex and advantage get pretty complicated).
Natural selection can’t see the future or act for whole species. Each small change conferred an advantage to individuals in the environment they were in at the time.
neocortex
mammals have a more plastic neocortex and other vertebrates don’t have it at all.
new cortex
diagram
Live in complex groups
(mostly) - whales, carnivores, monkeys and apes tend to have more cortex
apes and monkeys have a lot of neocortex relative to rest of brain aswell as whales
But remember:
Each small change must have conferred an advantage to individuals in the environment they were in at the time.
So what drove initial expansion of neo cortex
ancestral mammals have less neocortex
early primates
Primates became diurnal (active in daytime), with large expansion of visual, touch and motor capabilities. whereas ancestral mammals may have lived in caves and come out at night
in day can expand visual capabilities linked to expansion of neocortex.
Brain functions from an evolutionary perspective
Primate sensory systems are somewhat different from other mammals.
Compared to most mammals, we rely much more on sight than smell and hearing
Primate visual cortex is relatively huge.
To take one example of a change
Our type of colour vision evolved. - we have a different kind of colour vision than other mammals
How do we get evidence about how and why environments shaped brain function?
the comparative approach
Case study in environment shaping brain function:
Ancestral vertebrates had excellent colour vision with 4 types of cone, potentially giving them 4-dimensional colour vision…(meaning they can see colour differences we can’t) - they can make more colour discriminations than we can
Many reptiles, birds, fish retain this…. (and so did dinosaurs)
Mammals reduced the number of cone types they have: marsupials to 2 or 3, placental mammals to 2, some mammals to 1…
animals with one type of cone live in dark environment eg sea, nocturnal - they can pick up fast movement - have a reflective block in retina - we don’t have this fully
marsupials - have varied colour vision. better colour vision as needs to know difference between flowers
colour vision goes along with different environments, tasks and lifestyles
Primates have bucked the trend and re-invented trichromacy (3-dimensional colour vision) - we have a medium and long-wave cone made out of long-wave cone.
why - advantage for finding fruit in foliage
how do we test - use the optimisation approach
Measuring the properties of the environment and modelling how they could be discriminated by different types of colour vision…
Tells us that our colour vision is optimal for finding fruit in foliage…
Other mammals do not rely on this job so critically, and have optimized their vision for other things…such as being sensitive in the dark.
apes - cortical expansion
The last common ancestor of monkeys and humans probably had ~1.5 billion neurons in its cerebral cortex; you have about 16 billion.
Ancesteral structures co-opted for new uses
diagram in notes
Brain functions from an evolutionary perspective - case study: memory systems
diagram
‘As a series of our direct ancestors faced the problems and opportunities of their time and place, their brains developed specialized representations thathelped them survive. Through inheritance across millions of years, these representations—in modified form—made human memory what it is today. Nothing designed, intended, or ordained human memory to have its current character. Indeed, each of the key representations began by doing something quite different from what it does today’
*Navigational representations, which originally guided vertebrates through their watery world, established the foundation for participatory memory;
*Feature representations, which first guided foraging based on distant sights and sounds, later empowered the generalizations, concepts, and categories of cultural memory;
*Representations of the “self,” which initially promoted social cohesion and cooperation, came to underlie the sense of owning knowledge and participating in events: real and imagined.
Parietal lobe expansion: quantity relationships becomes ability to analyse relationships of many kinds
Temporal lobe expansion: features of food becomes ability to generalise about concepts and categories
Which brain areas support memory?
‘hippocampus and temporal cortex’
But that is a narrow view of memory systems..
Most of the brain supports memory of one form or another…
which areas show most expansion?
association cortex
Big brains are highly expensive
(so we must use it all)
Energy consumption: the brain is our most energy-hungry organ, consuming 20% of our energy, and has no energy store.
Deaths in childbirth: ~1%. Leading cause of female teenage death in developing countries.
Childhood mortality: human babies and children are vulnerable for a longer childhood than other animals. Mortality before age 15 is 30-40% in current hunter-gatherer societies!
Brain functions from an evolutionary perspective:
Case study: lateralisation
Many theories on why our brains are (partially) lateralized
Early theories (tool use, language) were based on wrong assumption that it is uniquely human
Now we know many animals have some degree of lateralization
It may have evolved in the earliest vertebrate brains, to serve efficiency
What was the nature of this bias that eventually led to the biases we see in humans for handedness, language, spatial and emotion processing?
One theory is feeding vs alerting. Or dealing with the usual vs unusual.
Two notes:
1. Remember that most of the brain is symmetrical.
2. The lateralisation of human brains has often been extrapolated to the idea of ‘right-brain and left-brain people’. There is not good evidence for this extrapolation
Development of evolutionary theory
- Darwin argued over time organisms originate and become adapted to their environments by biological means. This concept is biological evolution. Which are changes that take place in the genetic and physical characteristics of a population or group of organisms over time - it stands as the primary explanation of the origin of life. One of the most important books is on the origin of species by means of natural selection where Darwin shared his theory of evolution.
- There is evidence of life on earth a billion years after the formation of the earth 4.5 billion years ago (Eiler, 2007) and the human race has existed, in various forms, for over 10 million years. This timespan has seen a tremendous change in our physical appearance, our biology and our behaviour. Our brains have developed, our societies have become more sophisticated, our intelligence has increased, our ability to communicate has improved and we have developed language systems. These processes illustrate the ways in which we have evolved, and evolutionary theory seeks to explain why we have evolved in the way that we have.
- Darwins work has roots in biology but has influenced all the natural sciences especially psychology (Dewsbury 2009).
- Since the 1970s, some psychologists have become increasingly aware of the various ways in which biology can influence behaviour. Many behavioural differences among organisms, both within and across species, correspond to genetic and other biological differences. Understanding these differences and their evolution allows psychologists to understand behaviour in terms of its possible origins and adaptive significance – its effectiveness in aiding the organism to adapt to changing environmental conditions.
- Psychologists might research how past environmental conditions favoured gregariousness over a more solitary existence as a means of organising human culture and how the immediate environment influenced day-to-day sociability. They are interested in understanding both ultimate causes (from the Latin ultimatus, ‘to come to an end’) of behaviour – events and conditions that, over successive generations, have slowly shaped the behaviour of our species – and proximate causes (from the Latin proximus, ‘near’), namely immediate environmental variables that affect behaviour.
- By understanding how adaptive behaviour developed through the long-term process of evolution, psychologists can gain a more thorough understanding of our ability to adjust to changes in our immediate environment. To understand the present, we must understand the past – the history of the individual and the history of our species.
- We behave as we do because we are members of the human species – an ultimate cause – and because we have learned to act in special ways – a proximate cause. Both biology and environment contribute to our personal development.
Relatively recently, a field of psychology has emerged, evolutionary psychology (Tooby and Cosmides, 1989; Buss, 1995), which attempts to describe and explain how an organism’s evolutionary history contributes to the behaviour patterns and cognitive strategies it uses for reproduction and survival during its lifetime.
In the beginning - the voyage of the Beagle
- Darwin’s work is an excellent example of how observation and experimentation can lead to scientific breakthroughs.
- After receiving a degree in theology from the University of Cambridge, England, in 1831, Darwin met a Captain Robert FitzRoy who was looking for someone to serve as an unpaid naturalist and travelling companion during a five-year voyage on board HMS Beagle. The Beagle’s mission was to explore and survey the coast of South America and to make longitudinal measurements worldwide.
- During the voyage, Darwin observed the flora and fauna of South America, Australia, South Africa and the islands of the Pacific, South Atlantic and Indian Oceans. He collected creatures and objects of every sort: marine animals, reptiles, amphibians, land mammals, birds, insects, plants, rocks, minerals, fossils and seashells. These specimens, which were sent back to England at various stages of the trip, were later examined by naturalists from all over Europe.
Darwin did not form his theory of evolution while at sea. Although he was impressed by the tremendous amount of diversity among seemingly related animals, he believed in creationism, the view that all living things were designed by God and are non-evolving (Gould, 1985).
Origin of species
- Darwin was not the first person to propose a theory of evolution, but he was the first to amass considerable evidence in its favour. He became interested in artificial selection, a procedure in which particular animals are mated to produce offspring that possess desirable characteristics.
- For example, if a farmer wished to develop cattle that yielded the largest steaks, then they would examine the available breeding stock and permit only the ‘beefiest’ ones to reproduce. If this process is repeated over many generations of animals, the cattle should become beefier. In other words, in artificial selection, people select which animals will breed based on specific, desirable characteristics of the animals.
- As he pondered on whether there might be a natural process corresponding to the role that humans play in artificial selection, Darwin’s views on evolution began slowly to change. He believed that ‘selection was the keystone of man’s success in making useful races of animals and plants. But how selection could be applied to organisms living in a state of nature remained for some time a mystery to me’ (Darwin, 1887, p. 53).
- A year-and-a-half later, on reading Malthus’s Population, Darwin proposed that because the ‘struggle for existence’ continued in plants and animals, then favourable variations would be preserved and unfavourable ones would die out. The result of such ‘selection’ would be the development of new species (Darwin, 1887).
- This proposal contains the idea of natural selection: within any given population, some members of a species will produce more offspring than will others. Any animal that possesses a characteristic that helps it to survive or adapt to changes in its environment is likely to live longer and to produce more offspring than are animals that do not have this characteristic.
- Darwin was well aware of the significance of his discovery but did not publish his theory until 20 years later, taking great pains to develop a clear, coherent and accurate case for his theory.
- Darwin might have been even slower in publishing his theory had it not been for an intriguing coincidence. In 1858, he received a manuscript from the Welshman, Alfred Russel Wallace, another naturalist, outlining a theory of natural selection identical to his own.
Darwin’s colleagues suggested that he and Wallace make a joint presentation of their separate works before a learned society – the Linnean Society – so that each might lay equal claim to the theory of natural selection. This was done, and a year later Darwin published his ‘abstract’, which we know today as The Origin of Species. The book sold out on its first day of publication and has been selling steadily ever since. And although theories of evolution had existed before Darwin, he was the first to offer a systematic explanation for how evolution worked.
Darwin’s theory of evolution
Two concepts are central to Darwin’s theory of evolution: adaptation and natural selection. Adaptation refers to the ability of generations of species to adapt effectively to changes in the environment. Natural selection refers to the process whereby some variations in species will be transferred from one generation to the next, but others will not. The zoologist, Richard Dawkins, has likened the process of natural selection to a sieve because it leaves out what is unimportant (Dawkins, 1996).
Darwin’s theory has four basic premises.
1- The world’s animal and plant communities are dynamic, not static: they change over time with new forms originating and others becoming extinct.
2- The evolutionary process is gradual and continuous. New species arise through slow and steady environmental changes that gradually modify each species to its surroundings. When sudden and dramatic changes occur in the environment, a species’ ability to adapt is usually challenged. Some species adapt and live; others become extinct.
3- All organisms are descended from an original and common ancestor. Over time, the process of natural selection has created different species, each specifically adapted to its ecological niche.
Natural selection not only causes changes within populations during changing environmental conditions, but also acts to maintain the status quo under relatively constant environmental conditions.
Natural selection
- The essence of Malthus’s essay, which Darwin was reading when the idea of natural selection first occurred to him, was that the earth’s food supply grows more slowly than populations of living things. The resulting scarcity of food produces competition among animals, with the less fit individuals losing the struggle for life.
- For example, wolves that are agile are better able to capture prey than are slower packmates. Fast wolves will therefore tend to outlive and out-reproduce slower wolves. If a wolf’s tendency to run fast is a genetically controlled trait, it will be passed on to its offspring. These offspring will be more likely to catch prey and will therefore live longer and have more opportunities to reproduce.
- The ability of an individual to produce offspring defines that individual’s reproductive success – the number of viable offspring it produces relative to the number of viable offspring produced by other members of the same species.
- Contrary to popular interpretation, ‘survival of the fittest’ does not always mean survival of the most physically fit or of the strongest. The evolutionary ‘bottom line’ is not physical strength but reproductive success.
- Physical strength is only one factor that might contribute to such success. In humans, for example, good looks, charm and intelligence play an important role in an individual’s ability to attract a mate and reproduce.
- What is more, natural selection is not ‘intentional’. Giraffes did not grow long necks in order to eat leaves from trees, but those with longer necks who were able to reach the leaves successfully reproduced while the others died out.
Two aspects of natural selection – variation and competition – are the critical factors that determine whether any animal and its offspring will enjoy reproductive success.
Variation 1
- Variation includes differences among members of a species, such as physical characteristics (size, strength or physiology) and behavioural characteristics (intelligence or sociability). What factors are responsible for these sorts of variation?
- First, an individual organism’s genetic make-up – or its genotype – differs from that of all other individuals (except in the case of identical twins). As a result of these genetic differences, an individual organism’s physical characteristics and behaviour, or its phenotype, also differs from that of every other individual.
- Every individual’s phenotype is produced by the interaction of its genotype with the environment. In essence, the genotype determines how much the environment can influence an organism’s development and behaviour.
- For instance, identical twins have exactly the same genotype. If they are separated at birth and one twin has a better diet than the other, their phenotypes will be different: the better-fed twin is likely to be taller and stronger.
- However, regardless of diet, neither twin will ever become extremely tall or very muscular if they do not possess the genes for tallness and muscularity. Likewise, neither twin will realise their full potential for tallness and muscularity if they do not eat a nourishing diet.
- In this example, both the genotype (the genes related to tallness and muscularity) and a favourable environment (a well-balanced, nourishing diet) must be present for either twin to reach their full growth potential.
Phenotypes and the genotypes responsible for them may or may not be selected, depending on the particular advantage they confer.
variation 2
- In a study that investigated the relationship between rainfall, food supply and finch population on one island, Grant (1986) discovered that the amount of rainfall and the size of the food supply directly affected the mortality of finches having certain kinds of beak. During droughts, small seeds became scarce. As a result, the finches having small, thin beaks died at a higher rate than finches having bigger, thicker beaks. During the next few years, the number of finches having bigger, thicker beaks increased – just as the principle of natural selection would predict. During times of plentiful rain, small seeds became abundant, and the number of finches having small, thin beaks became more plentiful in subsequent years.
- Grant’s study makes two important points. First, although evolution occurs over the long run, natural selection can produce important changes in the short run – in the space of only a few years. Secondly, phenotypic variation, in this case differences in beak size, can produce important selective advantages that affect survival. Imagine if all the finches had small, thin beaks: during the drought, most, if not all, of these finches might have died. None would be left to reproduce, and these finches would have become extinct on this island. Fortunately, there was phenotypic variation in beak size among the finches, and because phenotypic variation is caused by genetic variation (different genotypes give rise to different phenotypes), some finches – those having large, thick beaks – had an advantage. Their food supply (the larger seeds) was relatively unaffected by the drought, enabling them to out-survive and out-reproduce the finches with small, thin beaks.
On the basis of this evidence, one might reasonably assume that all finches should have developed large, thick beaks. However, when rain is plentiful and small seeds are abundant, birds with small, thin beaks find it easier to feed. Under these environmental conditions, these birds have a phenotypic (and genotypic) advantage.
- Grant’s study makes two important points. First, although evolution occurs over the long run, natural selection can produce important changes in the short run – in the space of only a few years. Secondly, phenotypic variation, in this case differences in beak size, can produce important selective advantages that affect survival. Imagine if all the finches had small, thin beaks: during the drought, most, if not all, of these finches might have died. None would be left to reproduce, and these finches would have become extinct on this island. Fortunately, there was phenotypic variation in beak size among the finches, and because phenotypic variation is caused by genetic variation (different genotypes give rise to different phenotypes), some finches – those having large, thick beaks – had an advantage. Their food supply (the larger seeds) was relatively unaffected by the drought, enabling them to out-survive and out-reproduce the finches with small, thin beaks.
competition
- The second aspect of natural selection is competition. Individuals of a given species share a similar environment. Because of this, competition within a species for food, mates and territory is inevitable. Every fish captured and eaten by one bald eagle is a fish that cannot be captured and eaten by another bald eagle. If one bald eagle finds a suitable mate, then there is one fewer potential mate for other bald eagles, and so on.
- Competition also occurs between species when members of different species vie for similar ecological resources, such as food and territory.
- Competition for other resources indirectly influences reproductive success because the ability to find and court a suitable mate depends on the ability to stake out and defend a territory having an adequate food supply. The probability of a yellow-headed blackbird finding a mate and successfully rearing a family depends not only on its success in competing against other yellow-headed blackbirds, but also on its success in competing against red-winged blackbirds.
- Natural selection works because the members of any species have different phenotypes. Because these phenotypes are caused by different genotypes, successful individuals will pass on their genes to the next generation.
Over time, competition for food and other resources will allow only the best-adapted phenotypes (and their corresponding genotypes) to survive, thereby producing evolutionary change. This is what the theory would predict.
do people accept the theory of evolution?
- In the US, it is law that science and religion are taught separately and that banning the teaching of evolution is unconstitutional (Scott and Matzke, 2007).
- In 2007, the Council of Europe’s Parliamentary Assembly passed a resolution recommending that member states do not teach creationism as if it were the equivalent of science.
- Creationism – the rejection of the theory of evolution in favour of the belief that the world was originated by a Creator – has gained some momentum in the USA, although recent legal rulings suggest that evolution is fighting back. Creationism’s new incarnation is Intelligent Design but, to all intents and purposes, the terms are synonymous.
- Every year since 1985, the inhabitants of the US have been asked about the theory of evolution and whether they agree with it. In 2019 and 2020, 40 per cent and 54 per cent of people respectively accepted the theory of evolution (Miller et al, 2021).
- Miller et al also identified some predictors of this acceptance: younger people were slightly more likely to accept evolutionary theory, more men than women were, as were people who had completed 10 or more years of college (the strongest predictor). There has been a steady increase in the US of people attaining higher levels of education; the percentage of adults with baccalaureate qualifications, for example, was 20 per cent in 1988 but 35 per cent in 2018.
- Religious fundamentalism, perhaps not surprisingly, was correlated with non-acceptance over 30 years of the survey.
There was also a political division: in 2019, 83 per cent of liberal Democrats accepted the theory of evolution; 34 per cent of conservative Republicans did. The second highest predictor of acceptance was scientific literacy which may be explained by the increase in people taking mandatory science courses at college.
human evolution
- Reconstruction of human evolution is a difficult job, something akin to assembling a giant jigsaw puzzle whose pieces have been scattered throughout the world. Some of the pieces may have been lost for ever; others have become damaged beyond recognition; and those few that are found force continual reinterpretation of how the other pieces might fit the puzzle.
- Another way in which we can date our remains is via carbon dating. Animals breathe a form of (naturally occurring) radioactive carbon called C-14. When an animal dies, this carbon decays but at a constant rate. By examining the content of the carbon in the fossil or surrounding material, therefore, we can estimate the date of its existence.
- One problem here is that the amount of carbon found can be influenced by the amount in the air at the time.
- We can also analyse the changes in DNA between similar fossils – the less the change in DNA, the closer the two fossils are in time. But the best we can do is to make an educated guess about the evolution and lifestyles of our ancestors.
- Many biologists and natural historians of Darwin’s time believed that natural selection applied to all animals, including humans. Others insisted that although natural selection applied to other animals, it did not apply to humans. However, through study of the fossil record and recent developments in genetic research, we now know that our species is related genetically to other mammals.
The gorilla and the chimpanzee are our closest living relatives, and together we appear to have descended from a common ancestor. You may have heard it said that we share 99 per cent of our genes with chimps. In fact, what we share is DNA involved in the production of proteins. Ninety-nine per cent of our DNA in this regard is identical (King and Wilson, 1975).
Why, then, are we not exactly hirsute, whooping, tyre-swinging, banana-eaters?
The reason is that 98 per cent of the human genome is not involved in the production of proteins.
* The remainder is involved in the timing of production and how much is produced (these are called regulatory genes – there is a more detailed description of genetics later in the chapter).
* It is this percentage which causes the great difference between the species (Demuth et al, 2006). Humans also have multiple copies of genes that chimps do not (Pennisi, 2006). Therefore, while we have proteins in common, it is the way in which these proteins are organised that determines the differences between us.
* Our dependence on information from fossil remains and other archaeological artefacts is problematic. As Byrne (1995) has colourfully pointed out, much of what we conclude about our ancestors’ behaviour from archaeological findings is speculative; some is sensible speculation, but it is speculation, nonetheless.
* There is no way of empirically or conclusively demonstrating that artefacts were used in the way in which we suggest or that they indicate a specific way of living or behaving. In this sense, paleoanthropology – the study of human behaviour using information from fossil remains – is more like detective work than scientific work. ‘The reality’, Byrne argues, ‘is that we will never know with confidence the answers to many of the most important questions we would like to ask about what happened in the past five million years’ (1995, p. 6).
With this caveat in mind, the general pattern of evolution is thought to occur something like this. Our evolution from a common ancestor appears to have begun in Africa about two to four million years ago (Clark, 1993).
earliest human beings
- The earliest humans have been labelled Homo habilis (literally ‘handy man’). Homo habilis was small (only about 1.3 m tall and about 40 kg in weight) but was bipedal (able to walk upright on two feet). Compared with its predecessor – a species called Australopithecus (apes from the South) – Homo habilis had a larger brain and more powerful hands. The strong hands were well suited to making simple stone tools; hence the name ‘handy man’.
- A natural selection interpretation of such adaptively significant traits would argue that these early humans adapted to the environment in terms of creating shelter against the elements, catching and preparing food, and making weapons for self-defence.
Homo habilis was succeeded, about 400,000 years later, by Homo erectus (upright man). Homo erectus had a much larger brain and stood more erect than Homo habilis and had a more complex lifestyle.
- A natural selection interpretation of such adaptively significant traits would argue that these early humans adapted to the environment in terms of creating shelter against the elements, catching and preparing food, and making weapons for self-defence.
homo erectus
- Homo erectus was the first of our ancestors to establish regular base camps, which probably served as centres for social activities, including the preparation and eating of food. We cannot be absolutely sure that these interpretations are the correct ones, however. Homo erectus created more efficient and stronger tools than did Homo habilis, successfully hunted big game, and discovered and used fire. Fire enabled these early humans to cook food, remain warm in cold weather and protect themselves from predators.
Homo erectus’s use of fire, coupled with its apparent social nature and its ability to hunt and/or scavenge big game, permitted it to explore and settle new environments, including Europe, Asia, America and other parts of Africa (Spoor et al, 2007).
Homo sapiens
- The earliest known Homo sapiens (intelligent man) appears to have arisen about 500,000 years ago. The best known of the early Homo sapiens, Homo sapiens neanderthalensis (so-called Neanderthals, named after the German valley in which the fossils were discovered), lived throughout Europe and Central Asia between approximately 300,000 and 35,000 years ago.
- Neanderthals constructed small huts from bones and animal skins and sometimes burned bones as fuel. They were skilled big game hunters, tool makers and clothiers, and they had cultural rituals for burying their dead.
- In one Neanderthal burial site unearthed in France, a small boy was found positioned on his left side with a small pillow of flints under his head and an axe positioned by his right hand.
- Similar Neanderthal burial sites have been discovered, suggesting that these humans possessed cultural traditions not previously found in the prehistoric record.
- Informed speculation suggests that Neanderthals and modern humans (Homo sapiens sapiens) overlapped each other, although the origin of Homo sapiens sapiens is unclear. It seems to have arisen between 200,000 and 100,000 years ago.
- The Neanderthals became extinct around 25,000 years ago, with last evidence of their existence found in Gibraltar (Finlayson et al, 2006). What is clear, though, is that the Homo sapiens sapiens line has survived to flourish in all parts of the world, despite the presence of hostile climate, terrain and predators.
Some theorists have suggested that the variety of species is greater nearer the equator (Hillebrand, 2004) and that tropical environments create a museum and a cradle for species to flourish (McKenna and Farrell, 2006).
natural selection and human evolution
- The apparent success of the human species in adapting to a variety of ecological niches stems from the fact that natural selection has favoured two important human characteristics: bipedalism, the ability to move about the environment on two feet, and encephalisation, increased brain size.
- The ability to walk upright, which appears to have evolved in our early hominid ancestors over 4 million years ago (Boaz, 1993; Ruff et al, 1997), may have arisen from the need to stand on branches to reach food on other branches above (Thorpe et al, 2007). Bipedalism allowed not only greater mobility, but also freed the hands for grabbing, holding and throwing objects.
- The ability to grasp objects, in combination with an expanding capacity for learning and remembering new skills provided by a larger brain, led to advances in tool making, food gathering, hunting and escaping predators (Eccles, 1989).
- Early hominids had a brain volume of 650 cm3 (and they were about 155 cm tall). Current humans have a brain size of 1,500 cm3 and are, on average, 175 cm tall. It used to be thought that there was a relationship between body size and brain volume. However, the relationship is between relative size and brain volume.
- The increase in our brain relative to our size is called positive brain allometry. This began around 2 million years ago and has increased since – from 1,000 cm3 (Homo habilis) to (Homo erectus) to 1,350 cm3 100,000 years ago 450 cm3 (Homo sapiens). The increase may be attributable to better diet, better defence and, therefore, better survival. Children began to live longer, thus enabling the brain to be more fully developed.
The increase in brain volume is thought to be the result of increased surface area of the brain (the neocortex), but also the development of a structure near the brain stem, the cerebellum (Miller et al, 2022).
The linear relationship hypothesis has been challenged
by Smaers et al’s analysis of 107 extinct species and 1311 extant species spanning 21 orders. They examined where and when the shift in allometry happened and explored whether this was driven by brain size or by body size; that is, was a larger brain required for a larger body or did a larger body lead to a larger brain. They found that there were shifts in the slope of relative brain size.
* Changes in brain/body allometry seemed important for the diversification of mammalian species in the Cretaeous–Pateogne period, but the slope increased and decreased with later diversification.
* They highlight the curious case of the polar bear and the Californian sea lion; their mean body size is similar, but the brain of the polar bear is twice as large. The sea lion, however, has 3–6 times more volume in brain regions required for cognition. “Cognitive tests in polar bears,” they write, “are generally lacking” (p. 6). They suggest that rather than focusing on brain volume, it may be more informative to examine relative regional brain volume.
* As the brain became larger, more of its volume – especially the front part which is the most recently evolved – appeared to become devoted to thinking, reasoning, decision-making and other complex cognitive, ‘higher’ functions. Genetic studies (GWAS) have identified over 100 genetic loci responsible for variability in human cortex (Grasby et al, 2020).
Tilot et al (2021) attempted to determine the genomic changes that occurred by analysing surface area from 33,000 humans and how these were associated with genes. There was evidence of gene selection leading to increased surface area of the brain over 2000–3000 years and one specific gene selecting for the inferior frontal gyrus, the speech area.
Another important ability that emerged from encephalisation was planning:
the ability to anticipate future events and to consider the effects of these events on an individual or group of individuals. Such planning might have involved the organisation of hunts, the institution of social customs and events (such as weddings and funerals), and the planting and harvesting of crops.
* Over time, the interaction between bipedalism and encephalisation allowed humans to exploit new environments and establish well-organised communities.
* Advances in tool making and hunting, combined with the use of fire for cooking, protection and warmth, were adaptive: they helped humans to live longer.
* The increased lifespan of humans may have aided the gradual accumulation of wisdom as the older members of early human communities began to share their knowledge with younger members through language.
* Although the fossil record cannot tell us when language first developed, we assume that those who were able to communicate with others through language had a distinct advantage over those who could not.
Language originated and subsequently evolved because of its immensely adaptive significance (Pinker, 1994). As Skinner (1986) noted, language not only provided a simple means of warning others of danger, but also provided a means of communicating important information to others, such as the location of a good hunting spot or instructions on how to craft a tool. Perhaps the most important advantage conferred by language was its ability to reinforce the already strong social tendencies of early humans. Language is the foundation upon which all human cultures are built
