There has been much discussion of the nature-versus-nurture argument over recent years, and of what effects our genes and our environmental experiences have on our characters. As with everything, the extremes of both sides of the argument very seldom offer a complete answer. We live in an age where scientists have started to look at our genomes and those of the animals around us and study what happens in our brains as we develop. Although we are probably still missing a great deal of what is going on, it is becoming clear that, in fact, our genes can be switched on and off by certain things in our experience or environment. Hence, our future is not set in stone when we are born – there is not a map for our lives and how we will live them, how we will react or develop. Rather, there are potential reactions that may or may not be switched on depending on our experiences. Experiences influence genes and genes may dictate how influenced we are by our experiences – a complex interaction that allows for a very wide range of final personalities and behaviors.
But it is not as simple as that! We are learning that there are certain critical or sensitive periods – times during which the wet cement of character can be set in different ways – but that some of these have a finite limit as to how wet the cement is. Once it is set, there may be little we can do to change those pathways of behavior.
Take, for example, extreme cases such as the behavior of geese, which bond to or imprint the first thing they see and follow this as their mother. When a chick imprints on its mother, memories are laid down and a series of changes occur on the left side of the brain that accompany imprinting – neurons alter shape, synapses (junctions between nerve fibers) form, and genes are switched on. If this part of the brain is damaged, the chick does not imprint on its mother. A neurotransmitter is also switched on but the receptor for this transmitter is switched off about ten hours later. Hence there is a limited time known as the critical period when changes to this part of the brain can occur and allow the chick to imprint on its mother.
Other research has found that children who have not had good vision early in their lives but have treatment to correct the physical problem in the eye later on never really learn to see as strong-sighted people do – they have not learned how to interpret what they see; it is too late. If the brain is not taught and programmed by experiences, it cannot interpret what the eyes see – the critical period has passed. Scientists have also found that in monkeys the brain is able to change as it develops during a certain period after birth – it can be shaped by experience – but then loses the ability to be so adaptable. Experience seems to switch on certain genes for the learning process of seeing.
Another example of a critical period is the taking on of an accent. The ability to absorb and change is easy for the young, but inflexibility sets in later on in life. Even if people have lived for fifty years of their adult life in a certain country, they may still maintain the accent of the country where they spent their first fifteen to twenty-five years. Indeed, the ability to learn language, with all of its grammatical complexities, may end at around puberty in humans. This has been demonstrated by several cases of feral children who had been kept alone or grown up on their own in the wild and had not been spoken to for up to the first thirteen years of their lives. They were not able to learn grammar or how to manipulate language even though they did learn a reasonable vocabulary. One of these children was found to be highly intelligent but never learned to speak. If the brain does not become trained by listening and responding to language, it does not develop. There seems to be a period after which it is simply too late for the brain to be able to make the correct pathways.
We use the term “critical” when there is some sort of genetic switch that limits the time during which learning can occur. While the first eight weeks of a cat’s life may not quite be critical to its learning to accept other species, this period is vitally important. If this sensitive time is missed, the cat can experience many problems in adapting to life with people.
During this sensitive period, a cat can learn to accept people, other cats, and other animals. Cats are also very adaptable to learning from new experiences during this time (a process known as habituation) as their bodies are not yet reacting to certain events with fear. This gives a kitten time to learn how to react and respond to different situations rather than being flooded by responses that urge it to run away. At seven or eight weeks old the kitten’s body primes itself to become much more reactive. Hence the cat has a limited period in which to process its brain to learn how it will deal with these kinds of experiences in the future. It is a time when the cat most readily picks up social behavior. For pet cats this means the socialization of kittens to other cats, humans, and other pets that the kitten is likely to have to live with as it grows and becomes an adult. It is also a time when the kitten learns how to deal with new objects and experiences in a confident manner – getting used to dealing with novel sights, sounds, feelings, and experiences.
In cats the critical sensitive period for socialization seems to be between around two and seven weeks of age. Thereafter, no matter how good the care and socialization, it is very hard to ever forge those pathways that will lead to a cat that is relaxed and happy around people and in its immediate environment, with the usual occurrences such as household noise and movements. This is very important, especially for breeders. Breeders need to ensure that their kittens have regular handling, which has been shown to speed up various physical and behavioral traits and generally to reduce fearfulness. It is important that kittens meet more than one person – encounters with at least four people will help them to be relaxed with humans in general instead of just one or two selected people. In turn, the people also need to spend time with kittens – kittens handled for forty minutes a day have been found to be more attached to people than those handled for fifteen minutes a day. However, you don’t have to overdo it -spending longer than forty minutes with a kitten did not result in the same increase in benefit. Of course, it won’t do any harm but, if your time is limited, aim for a minimum of about three-quarters of an hour.