When I see a type of dog, I can in many cases imagine in my mind’s eye a pretty consistent repertoire of characteristics and behaviours for each. But, in a ‘police’ identity line-up of, say black Labradors, I think I would have trouble recognising one from another in many cases. In a sense, we’re all leaves from one tree in that we all share similar anatomy and physiology with other mammals. For example, we all have one heart and two kidneys, the amygdala is always in the same relative position in the brain, and we all have the same neurotransmitters and neurotransmitter receptor sites that are altered by the same drugs. There are also similarities across the board in our psychology (and therefore behaviour) as well. For example, puppy dogs start to fear things they have not encountered before at around 7 weeks of age. For wolves it’s 3 weeks, kittens 4 weeks and humans 8 months.
That said, presented with 10 ‘identical’ Springer Spaniels in a ‘police’ identity line-up, I could identify my dog easily, and I’m sure the same would hold true for your dog too. What is it that makes your dog (cat, horse, rabbit, guinea pig, hamster, etc.) unique? For that matter, what makes you ‘YOU’?
For all of us, cats and dogs included, there are two forces at work that sculpt each of us out of a raw block of organic matter and shape who we are both physically and mentally:
- Nature – the genes we inherit from our parents
- Nurture – the environmental influences we encounter through life. From what out mothers ate and did through our gestation before birth to everything we experience throughout our lives and on to our eventual deaths.
At the time of writing (Autumn 2009) six mammals, humans, chimpanzees, mice, rats, dogs and cows have recently had their complete genomes sequenced and catalogued. In 2005 the genome of the dog was finally ‘cracked’ with a great deal of publicity and fanfare.
The genome of an organism is the sum of the entire genetic information inherited from its parents. Your genome consists of 22 chromosomes and an X chromosome from your Mother, and 22 chromosomes and either a Y or an X chromosome from your Father. So ‘YOU’ are made from the combination of these 46 chromosomes and your sex is determined by your Father.
If your Father donated an X chromosome then your ‘combo’ is ‘XX’ and you’re female, if he gave a Y then your ‘combo’ is ‘XY’ and you’re male. Chromosomes are each made up of millions of DNA (deoxyribonucleic acid) molecules (there are 2.5 billion units of DNA in the entire genome) strung together and some segments of this DNA within the chromosomes has been identified as the control centres for specific aspects of how you’re made.
These segments are your genes, and it was once believed that there were around 30,000 of them in the human genome, but recent research as reduced this number to around 20,000 to 25,000. As genes are switched on and off, they provide the ‘blueprints’ for creating protein, the building blocks of your physical self.
If you think of your genome as a book, then the chromosomes are its 46 chapters, the genes are the 20,000 words and the DNA are the 2.5 billion letters.
The researchers who decoded the dog’s genome tested 60 different breeds of dog and chose the Boxer as the least variable and so the most representative of ‘dogs’. The dog’s genome is about the same size as the human genome and that of other mammals – around 2.5 billion DNA units. The number of chromosomes in the average dog varies from 36 to 78 chromosomes, reflecting the variation within the species.
Similarity rather than difference is the rule when it comes to comparing the gene sequences of different species with one another. For example, we humans share 96% (some researches say it’s 99.4%) of our genome with chimpanzees, and 50% with a banana. Dogs differ from gray wolves by about 0.2%. So it’s these tiny little differences in gene sequences that make the big difference in what we turn out to be.
Traits within a species – the look of Labradors and their generally friendly, laid back personalities compared with the smaller and much quicker Patterdale Terrier for example – is determined by groups of genes acting together. Different genes within a group control how each of the unique ‘Labrador’ or ‘Patterdale’ physical and behavioural characteristics develop to make sure that the end result looks and behaves as it should! For example, the shape of the head, colour of the eyes, length and shape of the legs, type of tail and so on.
As genes duplicate themselves, nature allows for slight variations in how the resulting genes work in the next generation. Most of these changes have no effect, but some do change the organism’s ability, for the better or worse, to get on in its natural environment, and this is what natural selection (look up Charles Darwin and the Theory of Evolution if you’re rusty on this) operates on. This natural gene variation is also responsible for the different traits we see in our dogs, and indeed our fellow human beings. So two Siamese from the same litter may turn out looking identical, but if ever you’ve owned such a pair, I’ll bet that each has his own distinctive personality and ‘quirky little ways’!
It’s pretty obvious that from the second an organism is born, the environment, or nurture, gets to work shaping it and influencing how the ‘final adult product’ turns out. The difficulty for science has always been how to go about objectively picking out which ‘bits’ came from nature and which from nurture and measuring them, particularly in humans where there would be enormous ethical issues in experimenting on children. But nature has provided the perfect experimental subjects with twins.
In fact, for many pet species of animal, dogs, cats, rabbits, hamsters and so on, not just twins, but multiple litters are the norm. There are two types of twins – fraternal and identical. Fraternal twins are the result of the fertilisation of multiple ova by multiple sperm and they can be of either sex. Fraternal twins are what we see in litters of puppies where individuals may be genetically no more alike than if they had been conceived in a different litter by the same parents. Identical twins on the other hand are the result of the fertilisation of a single ovum by a single sperm that subsequently splits into two genetically identical parts and they are always same-sex; either both male or both female.
In humans the number of births that result in twins varies enormously, but a rough average is one in 35 births. Of these around 2/3 are fraternal and the other 1/3 identical twins. Identical twins in other species rarely, if ever, occur naturally, or have never been recorded. In dogs a few natural cases have recently been reported. What all this boils down to is that it makes human identical and fraternal twins the ideal subjects for the ethical study of the influence of nature over nurture on how an individual turns out.
Identical twins are effectively nature’s clones.
It’s pretty obvious that genes passed down from the parents are solely responsible for what their progeny turn out to look like and, apart from accidental injury, or intentional invasive body adornment, nurture plays no part. But what about personality and behaviour? Years of research on tens of thousands of both identical and fraternal human twins from birth right through to adulthood has shown categorically that genes really do matter psychologically as well. The data shows that identical twins share far more personality traits than fraternal twins, such as outgoingness, emotional instability, interests and acquired habits.
One of the most fascinating aspects of all this research is the data collected on identical twins separated at birth.
So, what all this information tells us is that genes are equally as important for behavioural characteristics as well as physical characteristics in humans at least, and it’s reasonable to assume that the same holds true for other species as well.
Statistically, identical twins tend to be around 80 percent the same in everything from stature to health to IQ to political views. The similarities are partly the product of similar upbringing. But evidence from the comparison of twins raised apart points rather convincingly to genes as the source of a lot of that likeness. In 1979 the most widely publicised study of twins separated at birth was carries out by psychologist Thomas Bouchard and colleagues, that chronicled the fates of about 60 pairs of identical twins raised separately. Some of the pairs had scarcely met before Bouchard contacted them, and yet the behaviours, personalities and social attitudes they displayed in lengthy batteries of tests were often remarkably alike.
The first pair Bouchard met, James Arthur Springer and James Edward Lewis, had just been reunited at age 39 after being given up by their mother and separately adopted as 1-month-olds. Springer and Lewis, both Ohioans, found they had each married and divorced a woman named Linda and remarried a Betty. They shared interests in mechanical drawing and carpentry; their favourite school subject had been math, their least favourite, spelling. They smoked and drank the same amount and got headaches at the same time of day.
Equally astounding was another set of twins, Oskar Stohr and Jack Yufe. Separated from his twin six months after their birth in Trinidad, Oskar was brought up Catholic in Germany and joined the Hitler Youth. Jack stayed behind in the Caribbean, was raised a Jew and lived for a time in Israel. Yet despite the stark contrast of their lives, when the twins were reunited in their fifties they had similar speech and thought patterns, similar gaits, a taste for spicy foods and common peculiarities such as flushing the toilet before they used it.
Adapted from a story in The Washington Post, Sunday, January 11, 1998
“Give me a child until he is seven and I will give you the man"
said St. Francis Xavier (1506-1552).
It takes no leap of faith to accept that, along with the genes, environment must also play a crucial role in how an organism turns out, but this gem of wisdom from Xavier implies something important that was even understood 500 years ago. That in humans, the first few years of life are more important for a child’s development than the rest of its life. We now know that the same is true for many animals, including mammals and birds. But how? And for that matter, why?
The brain is made up of about 100 billion neurons all connected, or synapsed to each other to create one of the most complicated structures known to man in which there may be 1,000 trillion synapses!
These connections are anything but random and haphazard; in fact each one is incredibly precise. Many of these connections are made as the foetus develops in the womb, driven by the genetic programs of nature. However, many other synapses form only after birth and must be activated by external stimuli (vision, hearing, touch and so on) in order to develop and become fully functional.
So, if the mature brain was a beautiful sculpture, it started life as a rough brick of clay and the hands of nurture moulded and sculptured it into a priceless masterpiece. And all this sculpting has a ‘sell-by date’ – it must be complete within a relatively short timeframe of the animal’s early life.
In 1935 embryologist Hans Spemann won the Nobel Prize for his work on developing amphibian embryos. Spemann showed that when a section of early embryo was transplanted from one place to another it caused this tissue to take on the identity of the tissue over which it was implanted. He also found that this phenomenon only occurred if transplantation occurred within a well defined and narrow time frame of the embryo’s early life, and once the transformation had occurred it could not subsequently be reversed by returning the tissue to its original location. The transplanted tissue had been irreversibly physically altered by the transplantation, and this could only occur during a critical period of the embryo’s development.
At around the same time zoologist Konrad Lorenz discovered a similar natural process in baby geese. When the goslings emerged from their eggs, they became socially attached to the first moving object they saw, following it around as though it was their mother.
He called this imprinting, suggesting that the ‘mother-image’ was somehow etched permanently into the gosling’s brains. And, like Spemann’s embryos, imprinting would only happen within a specific time window – the first 2 days of life in the case of Lorenz’s goslings, after which they would not imprint on anything and would likely perish as a result. Lorenz called this window the critical period of social attachment.
The work of Spemann and Lorenz stirred up enormous interest for developmental psychologists because of it’s implications on early child development, and the search was on to better understand the mechanisms behind these ‘critical periods’.
In 1981 David Hubel and Torsten Wiesel received the Nobel Prize for their research on the development of the mammalian visual system which greatly broadened our understanding of the vital role of early experiences on the development of many species.
Actually, some of these periods are less critical than others, and it’s useful to think of these ones as ‘sensitive periods’. There is an important difference between a critical period and a sensitive period of development.
is a ‘window of opportunity’ during which a specific event must occur in order for that stage to proceed normally. For example, children born with congenital cataracts must have them removed so the eye can function normally by ‘seeing things’ before a year or so of age.
Even if the cataract is removed after this critical period, vision will never be acquired in that eye, not because the eye itself is defective, but because the visual cortex was never stimulated to develop properly and process visual signals.
Compare this with people who develop cataracts as adults that render them blind for sometimes years before they are finally removed. Once removed, site is immediately restored and is as good as it ever was. This is because the visual cortex was stimulated normally during early childhood.
is a ‘window of opportunity’ during which, if a specific event occurs, that stage of development would proceed more readily than if the event occurred at some other time. For example, learning a second language, and being able to speak it fluently with the native accent is much easier for children at an early age. Remarkably, the same cortical language centre of the brain is used in these children for both their native and the second language. In older children and adults however, the second language is located in a new language centre quite separate from the native language centre. The optimal sensitive period for learning a new language is up to around the time of puberty, after that, it’s much harder.
Maternal behaviour is obviously vital for the survival and wellbeing of the young. But there’s another, equally important side to this story – the attachment of the offspring to their parents (the mother in most mammals).
Like many mammals, humans are a social species and naturally form strong, life-long bonds with their conspecifics. We don’t waste any time and get right down to it from the moment we are born, where we form a strong bond with those caring for us.
So strong is our ‘human-centricity’ that there’s even a specific area of the brain (called the fusiform face area; we came across this on the Student Resource Centre for Unit 3) dedicated to recognising faces. From the moment we first open our eyes, it’s ready and waiting to seek out a ‘face’.
At around 8 months old, as object permanence is developing and babies are becoming more mobile, something off happens. They develop stranger anxiety – a fear of strangers. By 12 months most babies will cling to a familiar caregiver when frightened, and after a separation will be all hugs and smiles when reunited.
It was first believed that social attachment was simply the result of reinforcement – the food supplied by the caregiver was the primary reinforcer, and the caregiver was merely a secondary reinforcer. This was shown not to be the case by Harry and Margaret Harlow who, in 1959, conducted a cruel experiment on baby Rhesus monkeys. In order to test the relative importance of food versus contact, baby monkeys were raised in isolation with 2 artificial mothers placed in the cage with them. One was made of bare wire mesh with a rough wooden head and had a milk feeding bottle attached to it. The other was made of soft, velvety cloth that the baby could cling to, but had no milk. The infants overwhelmingly preferred the soft mother and would only visit the wire mother to feed. This soft mother was also more effective in decreasing the youngsters fear and the infant would explore more when the cloth mother was present. So, softness and warmth is more important than nourishment.
In order to develop normally, a monkey must have some interaction with an object to which it can cling during the first months of life – during a critical period. For monkeys clinging is a natural response and reduces stress.
The Harlow’s found that the monkeys that survived being raised in isolation for a year never recovered – they were withdrawn, fearful and never managed to interact socially with other monkeys. However, if they were brought up in isolation, but were placed in a room with a couple of other baby monkeys for just 20 minutes a day, they grew up normally.
In the 1980’s a shocking story emerged about the deprivation of children in Romanian orphanages that had striking similarities to Harlow’s monkeys published 20 years earlier. Children reared in isolation for the first 8 months of life without the opportunity to form attachments are generally damaged for life.
Feral children have also offered scientists a unique opportunity to study the effects of social deprivation.
What happens when a child initially forms a strong attachment to its mother and is then separated? Studies on adopted children show that 6 to 16 month-olds would not eat, or sleep properly and had difficulty in forming new bonds with their foster mothers. However, when checked again as 10 year-olds, these children had grown up normally with no apparent social deficits. Children older than 2, on the other hand, had much more difficulty adapting to and forming social attachments with their foster mothers. Clearly, this data has serious implications for a fostering system that moves children around from one home to another before they can develop strong attachments to any one fosterer.
In 1965, John Paul Scott and John Fuller published a book documenting the largest and most well documented social experiment ever undertaken on a pet species, dogs, conducted over a 20 year period at the Roscoe B. Jackson Memorial Labs in Bar Harbor, Maine, USA.
Scott, J. P. & Fuller J. L. (1965). Genetics and the social behavior of the dog. University of Chicago Press, ISBN 0-226-74338-1.
It’s no exaggeration to say that everything you’ve heard or read about the social requirements for a litter of puppies to grow into well balanced dogs, and by extrapolation of this data, a litter of kittens to grow into well balanced cats, will have been based on this important research.
Scott and Fuller originally identified 4 key stages in the development of puppies – the prenatal period, the neonatal period, the transition period, and the socialisation and juvenile period. Practically, we can ignore the prenatal period, that time from conception to birth, and update and refine the other 3 periods into these 5:
- The neonatal period: 0 to 14 days.
- The transitional period: 2 to 3 weeks.
- The socialisation period: 3 to 12 weeks.
- The juvenile period: 12 weeks to sexual maturity.
- The adult period: sexual maturity onwards.
Here are some of the findings they documented for puppies in no particular order:
- Puppies can be socialised to humans in just two 20 minute sessions per week.
- Puppies quickly increase their social contact with an unfamiliar stimulus between 3 and 12 weeks, but there is a more sensitive period between 6 and 8 weeks. This coincides with the onset of fear in strange situations.
- The best time to expose and socialise puppies is between 6 and 8 weeks, and this would be a good time to remove them from the litter.
- Puppies should be introduced to all the conditions they are likely to meet as adults by no later than 12 weeks.
- Puppies kept in restricted conditions until 14 weeks displayed various phobias. Reared with little or no human contact they developed a fear of humans that was incredibly difficult to overcome, if at all.