Tuesday, 25 November 2014

The Social Brain Hypothesis

What caused human brains - and those of other apes - to grow so large? One theory is that it resulted from the complexity of our environment - the day to day problems that our ancestors would have encountered in foraging and survival: Where are the fruit trees? Which ones did I pick from yesterday?

Another idea - the social brain hypothesis - is that the complexity of our social groups require a big brain to keep track of, especially when the group is large - a bigger group means more relationships to remember.

Doing either of these things well could potentially lead to a survival advantage, but which actually triggered the evolution of our unique brain size? Dunbar (1992) put the two theories to the test by comparing both foraging area and group size with neocortex ratio - the proportion of brain neocortex to other brain areas (considered a better measure of overall 'braininess' than absolute brain size or brain:body ratio).

A clear correlation was found - a bigger group meant a larger neocortex ratio, supporting the social brain hypothesis. In contrast there was no clear relationship between brain size and environmental complexity. It would appear that primates with larger social groups need larger brains in order to keep track of relationships. That is not to say, as Dunbar comments, that those large brains couldn't then be useful for dealing with environmental problems - but he does not feel it was the evolutionary driving force (Dunbar, 1998).

Chimps, like humans, are highly social animals. Image
by Benjamin Jakabek

Human Groups

Since the early work with other primates, Dunbar began to question whether the same principle would apply to human social groups. To fit with the ratio that had been found, a group size of around 150 would be predicted (Dunbar, 1998). In the modern world, however, it is difficult to define what constitutes our social group. Work colleagues? Friends and family? Neighbours? However, looking at hunter-gatherer tribes and at historical settlements, groups of around 120-150 members abound (Dunbar, 1993).

In a neat application to the modern world, Hill and Dunbar (2003) looked at the size of networks to which people send Christmas cards. It fitted the theory - 153.5 was the mean total population of the households receiving cards from any individual. This was only a fraction over the predicted maximum number - and in practice, senders of cards would probably not know every member of a recipient household equally well.

More recently, other researchers have started to look at new technology and social media, to ask whether technological developments have expanded the size of our natural social network. It appears that they haven't - despite the large number of contacts people often establish on Twitter, the number they regularly communicate with remains under 200 (Gonçalves et al., 2011).


The key idea from the social brain hypothesis is that evolution has determined a cognitive limit on what we can do; just as we have other mental limits such as short-term memory capacity, the brain is simply not capable of maintaining a greater number of close social relationships.

What does this number mean in practice? An obvious question to ask is how close a relationship has to be to count within the number. Do colleagues and extended family count? Just how do we define who is in our 150 and who is not? According to Dunbar, a simple way to look at it is as "the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar" (Bennett, 2013).


Dunbar's number does seem to be applicable to a large number of situations, from historic communities to hunter gatherer tribes, from the size of army units to Twitter engagement.

However not everyone is convinced. A correlation between brain size and social group size does not prove that there was an evolutionary cause-and-effect. And de Ruiter et al. (2011) have argued that although the neocortex plays an important role in social functioning, its size does not directly determine social skills.

It could also be argued that Dunbar has cherry-picked examples that fit the theory post-hoc, and that had the number from the correlation calculation been different (say 250), he would have been able to find examples of human communities to fit.


Bennett, D. (2012). The Dunbar Number, From the Guru of Social Networks. Retrieved 20/11/2014 from: http://www.businessweek.com/articles/2013-01-10/the-dunbar-number-from-the-guru-of-social-networks

Dunbar, R.I.M. (1992). Neocortex size as a constraint on group size in primates. Journal of Human Evolution, 22, 469-493.

Dunbar, R.I.M. (1993). Coevolution of neocortical size, group size and language in humans. Behavioural and Brain Sciences, 16, 681-735.

Dunbar, R.I.M. (1998). The social brain hypothesis. Brain, 9(10), 178-190.

Gonçalves, B., Perra, N. and Vespignani, A. (2011). Modeling Users' Activity on Twitter Networks: Validation of Dunbar's Number. PLoS ONE, 6(8): e22656. doi:10.1371/journal.pone.0022656

Hill, R.A. and Dunbar, R.I.M (2003). Social network size in humansHuman Nature, 14(1), 53-72.

de Ruiter, J., Weston, G. and Lyon, S.M. (2011). Dunbar's Number: Group Size and Brain Physiology in Humans Reexamined. American Anthropologist, 113(4), 557–568.

Friday, 14 November 2014

How Neurons Interact

The human brain is composed of several different types of cell, but the one that psychologists are primarily interested in is the neuron (nerve cell). There is a vast network of these cells in your brain - between 80 and 100 billion of them - and it is responsible for controlling every aspect of your behaviour.

A neuron. Image includes a close up of the synapse, i.e. the
connection with a neighbouring neuron. Source: here.

Of central importance to understanding these cells is the study of the way that they communicate with each other. When stimulated by neighbouring cells, each neuron sends out a small electrical current called an impulse. This travels along the nerve fibre, the 'axon', and then triggers the release of chemicals called neurotransmitters. These are then picked up by receptors on other cells.

This apparently simple process is the building block of all our psychological processes and behaviour.

Sunday, 9 November 2014

Australopithecus - an early human ancestor

Our ancestors split apart from the ancestors of modern chimpanzees and bonobos (pygmy chimps) around 6-7 million years ago. After that time, several species of early humans - known as 'hominids' - evolved, and each eventually became extinct as newer species evolved.

Australopithecus was one of the earliest known type of hominid, and one for which there is substantial fossil evidence.

An artist's impression of how a group of Australopithecus would
have looked.  Image source here.

There were several species of australopithecines, living at different times and in different areas. All are thought to have lived largely or entirely in the eastern half of Africa, ranging from modern-day Egypt in the north, to the southern tip of the continent. As the climate changed, they became adapted to living in a savannah environment, rather than in a rain forest like their ancestors.

The best known species are:

  • Australopithecus anamensis: the most chimp-like species, these individuals lived around 4 million years ago. Over 100 fossil bones have been found.
  • Australopithecus afarensis: had a more human-like skeleton than earlier hominids and seems to have been less well adapted for climbing trees, but was otherwise quite similar to chimps. The most famous skeleton fossil is Lucy.
  • Australopithecus africanus: similar to the above but evolved later, and had a larger brain.

It is generally accepted that australopithecus africanus was the ancestor of later of the first member of the genus Homo i.e. homo habilis (Leakey, 1981), but as with other events for which we only have sparse fossil evidence, the exact timing and interrelations of different early hominid species is still a matter of scientific debate. It was not until a later species of hominid - homo erectus - that early humans began to spread throughout the world.


Leakey, R.E. (1982). The Making of Mankind.  London, Sphere Books Limited.
Wolpoff, M. H. (1999). Paleoanthropology. New York: McGraw-Hill.

Wednesday, 1 October 2014

BPS guide to style and references

I love this resource from the BPS - it's an essential writing guide for all UK-based Psychologists and Psychology students:

The British Psychological Society Style Guide

What is it?

The guide does 2 main things:
  • Lists dos and don'ts for academic writing in Psychology.
  • Provides the standard format for references lists for a range of sources: books, journals,  website etc.
This establishes a standard style for academic writing, and helps you to ensure that your reports and publications are in the standard format when you submit them!

Image by Brenderous


When to use capitals? How to abbreviate? How to punctuate in-line citations? The guide provides useful tips and ways to avoid common errors, such as:

"et al." - should be in italics
Don't capitalise the names of concepts or theories e.g. 'working memory model' is preferred to 'Working Memory Model'.

Writing the References Section

Writing references can be a bit of a painful process... However the BPS guide explains very clearly how they should be set out, with dozens of examples.

I do look forward to seeing an update with more examples of how to cite websites, though. The current examples don't cover youtube clips, blogs etc.

See also: Simple guide to citing research studies.

Friday, 1 August 2014

Types of Sampling in Psychology Research

Ok, this is quite a technical topic, not one that will attract hundreds of fascinated readers to this blog, I know! But Psych students really need to understand the main types of sampling for school/university studies.

The same principles will also apply to other subjects where you conduct primary research on people.

What is sampling?

Sampling means selecting people to take part in your research. There are two key steps:

  • First, define the group of people that you want to study. Perhaps you live in London and you want to do a survey on elderly people. This is know as the 'population' for your research. However, you need to define it specifically. Instead of 'elderly people', you could say 'adults aged 70+ living in London'.
  • Now you have to pick a smaller group from this population, and conduct the research on them. Unless the population is very small, you can't study all of them! This smaller group is called your 'sample'.

An analogy...

If you have done Geography/Geology at school and collected rock samples, the concept is very similar. Rather than taking the whole rock/mountain, you collected a small piece and studied that.

The problems are also similar. What if the area of the mountain that you collected the rock sample from just happened to have a different type of rock than 99% of the mountain? Perhaps that rock was moved there by a glacier, and originated in a different place. The problem is that the sample is not representative of the whole. The results of the study on that rock sample can't be generalised to the whole mountain!

The concept of sampling applies to other subjects. Image: luigi alesi

It is very similar in Psychology. In the above example, if you selected a sample of elderly people by asking your grandmother's friends, they might not be representative of the whole population of people aged 70+ in London. Perhaps they are more affluent, in better health, or better educated than the average? Perhaps they are not as ethnically diverse as the whole population?

If your sample is not representative of the population, then it is difficult to generalise the findings of your research. What you find out might be true of your sample, but it may not be true of the whole population.

To put it another way, your sample is biased!

Types of sampling

The example above - sampling family or friends - is called an 'opportunity' or 'convenience' sample. Other sampling methods can get a much more representative sample, and, therefore, better data! Here are the main types to be aware of:

  • Random sampling: this means that everyone in the population studies has an equal chance of being chosen. This is a lot more difficult than it sounds! How do you ensure that everyone has exactly the same chance? Putting all the names in a hat might work, but not if there are 1000s of names! Psychologists typically use a random number table, together with a numbered list of members of the population. But what if the people you randomly select don't want to take part in your study? The problems are obvious!

  • Stratified: Here, the researcher makes sure that groups within the population are represented fairly within the sample. For example, having a 50-50 mix of males and females. it may depend on what is important to the research. If religious belief was likely to affect the results, then researchers may try to ensure that their sample had the same proportions of religions as the population as a whole.

  • Systematic: A systematic sample involves picking people at fixed intervals from a list of the whole population. So if you have a list of 1000 students in your year and pick every 50th name, that is a systematic sample.

These other types are less representative, but often used:

  • Opportunity: as described above, this is where participants are chosen on the basis of convenient availability. This might mean approaching people who walk past and asking them to take part. Like fishing in a lake, you take whatever comes along! This tends to lead to a biased sample, but is often used because it is quick and easy to do.

  • Self selecting: Also called 'volunteer sampling', this is when people come forward to take part in your study rather than you finding them. Milgram's (1963) study of obedience used people who responded to an advert, and were therefore a self-selecting sample. They may differ from average members of the population in various ways, for example, by being more interested in helping scientific research, or more in need of the money paid to participants!

  • Quota sample: similar to stratified sample, but here you simply ensure that you have some from every category (e.g. every religion) rather than keeping the proportions the same as the population. It may be that some groups have a very tiny population, so you set a minimum 'quota' to ensure that they are not missed out. For example, you might select two people from every religion, regardless of how common those religions are.

Syllabus note

For Scottish Higher, you should be aware of all of the above types. For A-Level, all except quota are included. At university level, these will cover you well at least for 1st and 2nd year.

To conclude...

In some situations, an opportunity sample might be adequate. A random sample is ideal, but has many practical problems in obtaining one. A good compromise might be to use a stratified sample.

Many thanks to the University of California, for permission to use their images on this post. Read their article on sampling here.

Any questions, feel free to ask in the comments!

Tuesday, 1 July 2014

Simple guide to citing research studies

At the end of every report or article in Psychology, the author puts a list of references, giving the sources of information and ideas mentioned in the text.

But how should you format them? Every reference list that you look at seems to be slightly different!

This post is not meant to be a complete guide, but it should cover the vast majority of sources of that new Psychology students will need to cite, because these tend to fall into three categories: books, journal articles, and websites.

A reference list helps a reader to find your sources. Image by Farrukh


Author(s), initials (year). Title of book. Place of publication: publisher.

  • Example: Selye, H. (1956). The Stress of Life. New York: McGraw-Hill.

Author(s), initials (year). Title of article. Journal Title, issue number, pages numbers.

  • Example: Tajfel, H. (1970). Experiments in intergroup discrimination. Scientific American, 223, 96-105.

Author(s), initials (year). Title. Retrieved (date) from (url).

What about capitals and italics?

The convention is to use italics and capital letters for the title of a book or journal, and italics for the journal's issue number, as with the examples above. Otherwise just use capitals as in everyday English grammar.

Where do I find the place of publication?

Usually this detail appears just inside the front cover, before the contents page of a book.

Is this true in all countries?

This style of referencing is called Harvard Style and is used in Psychology throughout the world. The examples above are based on the British BPS format, and there are minor variations in other countries- check with your school/university, but above all, try to be consistent!

What should be in the references section?

Only things that are mentioned in an 'in line citation' during your text, e.g. "Smith, 2000". All such citations should link to a full reference at the end. Nothing else at all should appear in your reference section - it is not a general bibliography, so don't include background reading.

What if there is no name?

If the source is an organisation rather than an individual, use that instead of surname, e.g. Wikipedia (2014).

Any questions, please leave them in the comments!

Tuesday, 24 June 2014

Have we evolved to fear snakes and spiders?

A phobia is a strong and irrational fear of something, a fear which is out of proportion to the dangers presented. If it is irrational, then why do we have them?

The psychology of phobias has been influenced by some of the biggest names in the field - Sigmund Freud felt that a phobia is the result of a repressed unconscious fear of one's parents (Freud, 1909), while the eminent behaviourist John B. Watson thought that while fear was a basic human emotion, any specific fear could be learned or unlearned through experience (Watson and Raynor, 1920).


Later, researchers began to think that our evolutionary past might play a major role in phobias. People tend to develop phobias of things which would could have been harmful for our ancestors, such snakes, spiders or heights. In contrast, it seems to be much rarer to have a phobia of things which have only recently presented a danger, e.g. cars, guns or electricity.

The idea that evolution has prepared us to fear certain harmful things is called preparedness theory, and it was proposed by Seligman (1971).

Mineka research on monkeys

Susan Mineka and colleagues conducted several studies of rhesus monkeys. They noted that when brought up by a parent who feared snakes, infant monkeys in captivity did not develop a fear of snakes, while wild monkeys did. They reasoned that this was because the captive infant monkeys were never exposed to snakes, and so they did not get a chance to observe their parents' fear reactions (Mineka et al., 1984).

Rhesus monkeys in the wild. Image by Kai Yan, Joseph Wong.

To test this theory, Mineka and colleagues conducted a controlled experiment to see whether the infant monkeys could learn a fear. Using 5 wild-reared and 6 captivity-reared infants, they exposed them to their parents acting fearfully in the presence of a snake. The infants rapidly learned to fear the snake - and their new fear was found to be permanent!

This shows that fears can be passed on from parent to child.

Will a monkey learn to fear something irrelevant, like flowers?

How strong is this tendency to learn fears through observation? Researchers know that we can learn some evolutionary 'newer' fears from observation - Townend et al. (2000) report that parental anxiety about dental visits is a factor in whether children learn to fear the dentist, even though dentists did not exist in our evolutionary past. Would a monkey learn to fear an irrelevant stimulus like a toy rabbit or a bunch of flowers?

To test this, Cook and Mineka (1989) spliced a video of an adult monkey reacting with fear to make it look like it was afraid of one of the following four objects:
  • A toy snake
  • A toy crocodile
  • A toy rabbit
  • A bunch of flowers
Each of the four versions of the video was shown several times to a group of around 10 young monkeys (42 monkeys were used in total). Researchers then measured how long it would take the monkeys to collect food, if the toy from the video was placed beside the food. It was found that the time greatly increased when the toy snake or crocodile was present (i.e. these objects made the monkeys more wary) but there was no increase in time with the rabbit or flowers present.

It appeared that a monkey will only learn a fear though observation if the object is biologically relevant.


So it appears that it is much easier to learn a phobia if it is biologically 'prepared' - but learning some form of anxiety through observation is still possible without preparedness. As with other experiments on animals, though, it is important to be cautious about generalising the results of the above research to humans.

See also: Fear and ugliness of animals (Bennett-Levy and Marteau, 1984).


Cook, M and Mineka, S. (1989). Observational conditioning of fear to fear-relevant versus fear-irrelavant stimuli in rhesus monkeys. Journal of Abnormal Psychology, 98, 448-459.
Mineka, S., Davidson, M., Cook, M. and Keir, R. (1984). Observational conditioning of snake fear in rhesus monkeys. Journal of Abnormal Psychology,  93(4), 355-372.
Seligman, M. (1971). Phobias and Preparedness. Behaviour therapy, 2, 307-320.