Why are women better at food shopping than men?

Men do better than women at most tests of spatial awareness, but not all. A new study set in a farmer’s market shows that women outperform men at remembering the locations of food, particularly the most calorific ones.

Our evolutionary history makes women better at finding food in supermarkets than menWhen men and women do the grocery run, their evolutionary histories play out among the aisles of food in subtle ways. Women are more likely to remember where things are; men are better at plotting efficient paths through the smorgasbord of choice. These different abilities are the result of evolutionary adaptations that took place when we were still hunting and gathering.

The evolution of sex differences

The brains of men and women are clearly different, and rarely more so than in the realms of spatial awareness. In most tests of spatial ability, men routinely outperform women. But to Irvin Silverman and Marion Eals, this crude assertion crumbled under an evolutionary spotlight.

In 1992, the duo noted that our mental abilities were not created from a vacuum – they evolved to allow us to cope with different adaptive challenges. And for the men and women of our dim evolutionary past, these challenges were very different.

Back in the day, when we were still living as hunter-gatherers, men did most of the hunting while women excelled at gathering. And these jobs required very different spatial skills. Hunters, for example, needed to chase their prey over unfamiliar and winding routes; once they had killed, they needed to work out the quickest route home.

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Simple sponges provide clues to origin of nervous system

The possible origins of the nervous system have been found in the simple sponge, an animal with no nervous system of its own. Sponges carry the genetic components of synapses, which may have been co-opted by evolution as a starting point for proper nerve cells

Sponges are the most primitive of all animals. They are immobile, and live by filtering detritus from the water. They have no brains or, for that matter, any organs, tissues or nervous system of any sort. If you were looking for the evolutionary origins of animal intelligence, you couldn’t really pick a less likely subject to study.

Over time, evolution co-opted the early PSD of the sponge and used it to craft true nervous systems.So it was with great surprise that Onur Sakarya from the University of California, Santa Barbara found that sponges carry the beginnings of a nervous system.

With no neurons to speak of, these animals still have the genetic components of synapses, one of the most crucial parts of the nervous system. And their versions share startling similarities with those of humans.

Synapses (and proto-synapses)

Synapses are junctions between two nerve cells that are allow the cells to pass on signals to each other. Signals are carried by molecules that cross the synaptic gap called neurotransmitters. When they reach the receiving cell, they come across an elaborate tangle of proteins called the post-synaptic density (PSD; labelled in red below). The PSD processes the neurotransmitters, among many other important roles, and allows the receiving cell to respond appropriately to the nervous signal

Sakarya searched for equivalents of the human PSD proteins in the genomes of other animals. For a start, he found an almost complete set in the starlet sea anemone (Nematostella vectensis). The anemone (like its cousins, the jellyfish) is one of the Cnidarians, a group of animals that have the most rudimentary of nervous systems. Finding PSD genes in them is surprising but reasonable.

The synapse relays signals from one cell to another.But Sakarya was really surprised when he found the vast majority of the PSD assemblage in the sponge Amphimedon queenslandica, an animal that doesn’t even have a nervous system! The sponge’s PSD proteins bore remarkable resemblances to those of humans and other animals, and were built of similar arrangements of domains.

One in particular, the PDZ domain, allows PSD proteins to recognise one another and assemble correctly. When Sakarya compared the structures of the human and sponge PDZ domains, he found that at the atomic level, the parts they used to interact with other proteins were almost 90% identical. So not only does the sponge have the full set of PSD parts, it can assemble them into a fully-functioning whole.

Pre-adapted

So what is the PSD, part of the nervous system, doing in an animal without one? Sakarya believes that the PSD is an example of exaptation, a process where evolution co-opts an existing structure for another purpose. Bird feathers are a good example of this – they evolved in small dinosaurs to help them regulate their body temperature, and were only later used for flight.

Exaptation can explain how complex, integrated structures like the nervous system can evolve. Rather than building the whole thing from scratch, evolution took ‘off-the-shelf’ components, like the PSD, and put them together in exciting new ways.

Sponges are the simplest of animals but even they have genetic components of synapsesIn the same way, the PSD of sponges is switched on in a type of cell called the ‘flask cell’. Flask cells are only found in sponge larvae, which, unlike the adults, are free-swimming. These cells could help the larvae to sense their environment, and could well have been a starting point for the evolution of neurons.

Sakarya cautions that there could be another explanation. Sponges could be degenerate relics of a more advanced branch of animals, that stripped away their complexity in favour of life in the (very) slow lane. In this scenario, the flask cells are evolutionary remnants of neurons proper.

Nonetheless, under both scenarios, these findings strongly suggest that the common ancestor of all living animals already has an early working version of the PSD. This practically pre-adapted it for the evolution of nervous systems. With minimal additional evolutionary steps, this early scaffold could have been transformed into the functional synapses that drive our thoughts today. The ancestor was pre-adapted to a future with neurons.

It’s worth noting that this discovery was only made possible because the genome of Amphimedon has been fully sequenced. In an age where genome sequencing could start to be taken for granted, this drives home the importance of sequencing a wide variety of living things that represent crucial junctures in evolution.

Reference: Sakarya, Armstrong, Adamska, Adamski, Wang, Tidor, Degnan, Oakley & Kosik. 2007. A post-synaptic scaffold at the origin of the animal kingdom. PLOS One 6, e506: 1-7.

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Related stories about evolution:
Of flowers and pollinators – a case study in punctuated evolution
Natural selection does a handbrake turn – quick evolution at work
Salamander robot walks, swims and sheds light on evolutionary step from sea to land
Human cone cell lets mice see in new colours
Living optic fibres bypass the retina’s back-to-front structure

Related stories about nervous systems:
Maternal hormone shuts down babies’ brain cells during birth
No new brain cells for you – settling the neurogenesis debate
Bats create spatial memories without making new brain cells

The evolution of animal personalities – they’re a fact of life

Animals have distinct personalities and temperaments, but why would evolution favour these over more flexible and adaptible mindsets? New game theory models show that animal personalities are a natural progression from the choices they make over hwo to live and reproduce.

Any pet owner, wildlife photographer or zookeeper will tell you that animals have distinct personalities. Some are aggressive, others are docile; some are bold, others are timid.

An animal’s reproductive decisions can determine if it is a hawk…In some circles, ascribing personalities to animals is still a cardinal sin of biology and warrants being branded with a scarlet A (for anthropomorphism). Nonetheless, scientists have consistently found evidence of personality traits in species as closely related to us as chimpanzees, and as distant as squid, ants and spiders.

These traits may exist, but they pose an evolutionary puzzle because consistent behaviour is not always a good thing. The consistently bold animal could well become a meal if it stands up to the wrong predator, or seriously injured if it confronts a stronger rival. The ideal animal is a flexible one that can continuously adjust its behaviour in the face of new situations.

And yet, not only do personality types exist but certain traits are related across the entire animal kingdom. Aggression and boldness toward predators are part of a general ‘risk-taking’ personality that scientists have found in fish, birds and mammals.

Life decisions affect personality

Max Wolf and colleagues from The University of Groningen, Netherlands, have found a way to explain this discrepancy. Using game theory models, they have shown that personalities arise because of the way animals live their lives and decide when to reproduce.

For an animal, success is measured achieved through living long enough to reproduce, and individuals constantly gamble their current success against their future one. They could reproduce now, or defer it to a later time when resources are more abundant.

The crux of Wolf’s theory is that those with a stable, assured future have more to lose by gambling, and are likely to be more risk-averse. Those with little to lose can afford to live fast and die young.

A model personality

Wolf tested this idea by using a mathematical model to simulate these choices and their consequences. The protagonist of his model is a fictional animal that lives in an area with many territories, some rich in food and others lacking it.

The animal can choose how thoroughly it wants to explore its habitat. If it is adventurous, it could find a lush and bountiful territory, but it will have less energy to raise young, and must postpone this to the following year. That may not be so bad – its new home will give it a ripe, long life and it will have many opportunities for breeding.

or a dove.He found that simulated animals picked one of two stable strategies. Some decided to explore thoroughly and hope for greater reproductive success in the future. Others decided to stay put, have young now and make the best of things, poor resources be damned.

Wolf then modelled how these two groups would react to decisions about risk, in a classic hawk-dove experiment. When faced with a predator or a rival, the animal could run away or back down (dove), which takes time and could lose it feeding opportunities or its territory. If it stood and fight (hawk), the likelihood of death or injury was greater but so were the rewards.

Sure enough, the explorers who were investing on future success, consistently evolved to be docile, timid and risk-averse, while those who reproduced immediately consistently became bold and aggressive. These patterns held up under a wide range of simulated conditions. Over time, they gave rise to stable individual differences and behaviour traits that were consistently linked with each other, the foundations of personality.

Objections

In New Scientist’s coverage of this story, Judy Stamp from the University of California, Davis, criticises Wolf’s work for only explaining extremes of personality. Obviously, animals are not always black hawks or white doves, but many shades in-between.

But Wolf’s study answers this too. In the most advanced version of his model, he accounted for the fact that behaviours are governed by many heritable genes. This generated a much more realistic and continuous spectrum of personalities. Even with this more plausible model, the same principle applied – the more an animal had to lose, the fewer risks it was prepared to take.

Wolf is now keen to see his theory tested in the field. He suggests that many other behaviour traits could be linked to aggression or boldness. Individuals that invest heavily in the present may be more likely to guard nests, care for their young or woo mates with conspicuous and costly displays.

 

Reference: Wolf, van Doorn, Leimar & Weissing. 2007. Life-history trade-offs favour the evolution of animal personalities. Nature 447: 581-584.

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Chimps show that actions spoke louder than words in language evolution

Chimpanzees and bonobos use gestures more flexibly and adaptively than other forms of communication. These gestures, and not words, may have been the starting point for the evolution of human language.

Hollywood cavemen typically communicate with grunts and snorts, reflecting a belief that human language originated like this and slowly evolved into the rich and sophisticated tongues we use today.

Chimps and bonobos have thier own vocabularies of gestures.But researchers from Emory University, Atlanta have found evidence that the origins of human language lie in gestures, not words. If they are right, then high-fives, V-signs and thumbs-ups could more closely reflect the beginnings of human language than conversations do.

The importance of gestures

All primates can communicate with each other through facial expressions, body postures and calls, but humans and apes are unique in their use of gestures. These go beyond simple postures or walking patterns – they are movements of the hand, limbs and feet, specifically directed at another individual.

We think of language as mainly spoken or written but gestures play an enormous, often overlooked role. After all, isn’t a speaker who waves their hands animatedly more engaging than one who stands motionless behind a podium?

And they are such an intrinsic part of the way we communicate that a blind speaker will make gestures normally to a blind audience, and babies use gestures long before they learn their first words.

To understand the role of gestures in the origins of human language, Amy PIllock and Frans de Wall decided to see how they are used by our closest relatives – the chimpanzee and the bonobo (the pygmy chimpanzee

How chimps and bonobos communicate

Bonobos may communicate with more sophistication than chimps.For one and a half years, they watched 34 chimps belonging to two separate groups, and 13 bonobos (right), again from two groups. Through painstaking analyses, they identified 31 different gestures and 18 different facial and vocal expressions.

The facial and vocal signals were very consistent between the two species. They were used in the same ways, and in very specific contexts, such as play, grooming or fights. For example, both chimps and bonobos scream when threatened or attacked, a gesture that is shared by many other primates.

This suggests that these signals are an evolutionarily ancient means of communication, and were probably used by the common ancestor that we shared with both chimps and bonobos.

Gestures on the other hand, were altogether more flexible. They were used in all sorts of situations and carried very different meanings depending on the context.

When a chimp stretches out an open hand (below), it can be asking for support during a fight or for a share of food during a meal. In the same way, a person raising his hand could be greeting a friend, surrendering, or answering a question in class.

Chimps use gestures more flexibly than other forms of communication.Chimps and bonobos also differed considerably in their vocabulary of gestures, with each species having its own ‘gesture culture’. The two groups of bonobos even used slightly different sets of gestures to each other.

Gestures and the origins of human language

Pillock and de Waal believe that these studies strongly position gestures as the starting point for human language evolution. In chimps and bonobos, gestures are more adaptable and flexible than calls or facial expressions.

They are relatively disconnected from specific emotions and can be more easily controlled. Facial expressions can give away big clues about a person’s emotional state in all but the best poker faces, but gestures can be used subtly or even deceptively.

Their adaptability means that gestures can be used in many ways and are free to pick up a variety of symbolic meanings. They pick up cultural differences easily, as shown by the very different ‘gesture vocabularies’ used by chimps and bonobos.

Pillock’s and de Waal’s experiments also support other studies which suggest that the language of bonobos is more sophisticated than that of chimps. For a start, their gestures show greater cultural variations.

While bonobos combine them with calls and facial expressions less frequently than chimps do, but they also respond much more strongly to these joint signals. Pillock and de Waal believe that the bonobos could be using these multiple signals more deliberately than chimps to subtly change the meaning of a facial expression or vice versa.

The chimps on the other hand, may just be using joint signals to say the same message more loudly. Among the great apes, the bonobos may deserve the silver medal for their language skills.

Reference: Pollick & de Waal. 2007. Ape gestures and language evolution. PNAS 104: 8184-8189

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Non-coding DNA drove human brain evolution by making nerve cells stickier

Most of our genome is made up of the poorly named ‘junk DNA’. New research shows that these sequences may have been vital in the evolution of human brains, by allowing our neurons to make better contacts with each other.

DNA, and little of it is 'junk'.Two months ago, a group of scientists found that the gene that has evolved fastest since our evolutionary split from chimpanzees is found in our so-called ‘junk DNA’. DNA is a code that tells our cells how to build their molecular workforce – proteins.

But the vast majority of our DNA sequence is never translated into proteins. While some considered this ‘junk’ DNA to be meaningless, recent research has shown that it makes important contributions to our most human of organs – our brains.

Now, Shyam Prabhakar and James Noonan at the Lawrence Berkeley National Laboratory have found further proof of the link between non-coding DNA and our mental evolution.

They studied over 110,000 stretches of DNA called ‘conserved non-coding sequences’ (CNSs), that are largely similar in a wide variety of animals. Of these sequences, 992 showed large numbers of changes that were specific to humans.

This number is much higher than would be expected if these DNA regions were drifting aimlessly in the evolutionary river. Their frequency is the mark of natural selection – these sequences must have changed for a reason.

To discover what this reason might have been, Prabhakar and Noonan looked at which genes these CNSs were in, and what they do in the body. They found that a large proportion of the genes in question were involved in the adhesion of neurons (nerve cells).

These genes are vital for the growth and development of our brains and allow neurons to make connections with each other, and with their surrounding framework of supportive cells.

The duo found a similar number of CNSs with chimpanzee-specific changes and many of these were also involved in nerve cell adhesion. But there was hardly any overlap between the chimp-specific and human-specific sequences.

Both lineages have developed nerve cells that make better contacts with each other, but have done so in separate ways using different genes.

It is possible that human and chimp brains have evolved different mental abilities to satisfy different evolutionary pressures. Identifying the precise role of the human-specific CNSs will help to test this possibility and it is the next big challenge facing Prabhakar and Noonan.

In the meantime, this research once again shows that non-coding DNA, far from being useless junk, was vitally important for the evolution of the human brain and its many unique abilities. Subtle changes in these sequences separate us from even our closest animal relatives.

Prabhakar, Noonan, Paabo & Rubin. 2006. Science 314: 786.
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Asymmetrical brains help us (and fish) to multi-task

The asymmetry of the human brain may allow us to cope with multiple demands that compete for our attention. The link between brain asymmetry and multi-tasking has now been confirmed in experiments with artificially-bred fish.

As you read this article on the internet, your computer is busy. You may be running multiple programs in the background, with email clients, anti-virus software or file sharing software all competing for valuable memory. The ability of computers to multi-task has grown substantially in recent years, as processors have become increasingly powerful.

Evolution has chartered a similar course, and humans have a particularly strong talent for dividing our attention among multiple priorities. Now scientists are showing that the asymmetrical differences between the two sides of our brain are essential for this ability to multi-task.

In the animal world, the ability to multi-task is a matter of life and death. Many species must be ever-watchful for food, while simultaneously looking out for predators who would view them in the same way.

Like too many open applications that slow down a computer, these multiple tasks compete for the brain’s finite resources. Those who survive life’s challenges are those with an edge at efficiently dealing with multiple demands.

The human brain - not symmetricalOne way of doing this is to use parallel processing – to delegate different parts of a problem to different pieces of hardware.

This is exactly the situation found in the human brain, with two asymmetric hemispheres associated with different mental abilities. And this ‘lateralisation’ is not unique to us, but seems to be present in all back-boned animals, from fish to apes.

An explanation for this asymmetry now becomes obvious – it may allow animals to multi-task, acting as a sort of cerebral division of labour.

(Un)evenly-brained fish

Marco Dadda and Angelo Bisazza at the University of Padova decided to test this idea, by looking at small freshwater fish called killifish. They bred different strains of this species with either symmetrical brains or asymmetric ‘lateralised’ ones.

The fish were kept in a special tank consisting of two parts separated by a trap door. In one half – the ‘feeding zone’ – the researchers placed a live brine shrimp for the fish to eat.

A killifishBoth strains were equally adept at catching the shrimp, but the lateralised strain gained a massive advantage when a predator was brought into play.

Dadda and Bisazza occasionally placed a tank containing the larger predator pumpkinseed sunfish in front of the feeding area, so that any killifish swimming across found itself face-to-face with a threat. When this happened, the symmetrically-minded ones took twice as long to catch their meals, but their lateralised peers took barely a second longer.

When the fish had to divide their attention between watching the predator and catching the shrimp, the lateralised brains acted as parallel processors, allowing them to cope with both tasks simultaneously.

Dadda and Bisazza confirmed this interpretation by carefully watching the fish as they swam after their meals. Killifish catch their food by approaching from the side, using one eye to monitor the prey.

In the absence of the sunfish, they were equally to strike from either side. But with the predator around, in 7 out of 10 times they snapped at the shrimp on the same side, watching it with one eye, and the predator with the other.

The pros and cons of asymmetry

In the case of the killifish in this experiment, partitioning roles to different parts of the brain seems to have brought clear benefits. But Dadda and Bisazza are quick to point out that the situation in the wild is less obvious.

In many cases, species with lateralised brains show lateralised behaviours, preferring to turn, keep watch or catch prey on one side of their body. Their other side is less often guarded, and natural selection penalises them for it by producing predators that prefer to approach from the unguarded side.

In these cases, regardless of parallel processing power, an asymmetric brain is clearly a disadvantage. The two scientists believe that the tipping point between these pros and cons comes when an animal has to perform difficult mental tasks.

Other studies have shown that asymmetrical brains endow wild chimpanzees with superior termite-fishing skills, and (equally wild) human children with better mathematical and verbal abilities than their classmates.

It may be that over the course of evolution, our brain’s halves started to work together more effectively as they became more different and specialised. It is ironic and sad then, that the opposite seems to hold true for the divergence of human cultures.

Dadda & Bisazza. 2006. Animal Behaviour 72: 523-529.