Adaptation refers to modification as a result of changed life circumstances.

Genes never produce behaviour directly, so genes are technically not for a behavioural trait, but associated with that behavioural trait. All the effects that genes have on behaviour occur through their role in building and modifying the physical structures of the body.

Genes affect the body’s development through, and only through, their influence on the production of protein molecules. A class of proteins called structural proteins forms the structure of every cell in the body. Another, much larger class called enzymes controls the rate of every chemical reaction in every cell. Genes are components of extremely long molecules of a substance called DNA (deoxyribonucleic acid). A replica of your whole unique set of DNA molecules exists in the nucleus of your body’s cell, where it serves to code for and regulate the production of protein molecules. Each protein molecule consists of a long chain of smaller molecules called amino acids. There are two types of genes. Coding genes: genes that code for unique protein molecules and regulatory genes which help suppress or activate coding genes and thereby influences the body’s development.

The environment is everything except for the genes and this influences the genes. Behaviour is influenced by the genes through the interaction with the environment. The environment is everything except for the genes. The internal environment influences the genes by certain gene activations for example. The external environment influences the genes by eating, for example, a different kind of foods. The genes then go on to activate or suppress development in certain physiological areas and this affects the behaviour.

Experience can activate a certain gene which then goes on to affect behaviour. The experience activates genes, which produce proteins, which alter the function of some of the neural circuits in the brain and thereby changes how an individual behaves.

Genotype refers to the set of genes an individual possesses and phenotype refers to the observable properties of the body and behavioural traits. If two individuals with the same genotype are exposed to different environmental conditions, they will have different phenotypes.

The genetic material (strands of DNA) exists in each cell in structures called chromosomes. When cells divide, other than sperm or egg cells, they do so by a process called mitosis. In this process, the chromosome copies itself before the cell divides so there’s an identical copy of the cell. When cells divide to produce sperm or egg cells, they do so by a process called meiosis, which results in cells that are not genetically alike. During meiosis, each chromosome replicates itself once, but then the cell divides twice.

When a sperm and an egg cell unite, the result is a zygote, which contains the full complement of 23 paired chromosomes. The zygote then grows, through mitosis. By producing diverse offspring, parents are reducing the chance that all of their offspring will die as a result of an unforeseen change in the environment. The only people who are genetically identical to each other are identical twins. Fraternal twins originate from two zygotes, where identical twins originate from one.

Two genes that occupy the same locus (location) can be identical to each other. If they are, they are homozygous and if they’re not they’re heterozygous. Different genes that occupy the same locus and can potentially pair with each other are called alleles. A dominant gene is one that will produce its observable effects in either the homozygous or the heterozygous condition. A recessive gene is one that will produce its effects in homozygous conditions only. Not all genes are recessive or dominant. It is possible for them to blend.

It is possible that diseases that only occur in a heterozygous state will persist in a gene pool because the benefit comes from carrying the disease, not having it. That is why the gene with only one recessive gene for the disease will be passed on the most, instead of the genes without the recessive gene for the disease or genes in a homozygous state with the disease (people who have the disease).

Scott and Fuller show that fearfulness in a certain breed of dogs is controlled by a single gene locus, by crossing the dogs and keeping track of the fearfulness. This way they could determine whether it was a recessive or a dominant gene that played it’s part here. Fear in dogs is not completely controlled by a single gene locus, but this one particular type of fear, the one they tested under controlled conditions, is a fear which is controlled by a single gene locus. It is not safe to say that other types of fear or fear in other conditions in dogs will also be controlled by the same single gene locus. Genes and the environment interact.

Characteristics that derive from variation at a single gene locus are typically categorical in nature (e.g: seeds are either round-shaped or wrinkled), but most anatomical and behavioural differences among individuals of any species are measurable in degree, not in type. They are continuous, rather than categorical. Examples of this are aggressiveness in mice and maze learning in rats. They can fall anywhere on the scale and they are not either aggressive or non-aggressive. The scores are divided over a normal distribution. Characteristics that vary continuously are generally affected by many genes and are therefore called polygenic characteristics. These characteristics are the results of both genes and the environment.

To the degree that individuals within a species differ in any measurable characteristic because of differences in their genes, that characteristic can be modified over time over successive generations through selective breeding.

The field of epigenetics examines gene-regulating activity that doesn’t involve changes to the DNA-code and that can persist through one or more generations. Epigenetic mechanisms are responsible for making sure that the right genes are activated at the right places at the right time. Epigenetics seems to be the primary mechanism by which experience modifies gene-action and thus behaviour.

The difference between artificial selection and natural selection is that natural selection is not driven by the needs of humans, but rather by the obstacles to reproduction that are imposed by the natural environment. Animals that have characteristics to help them overcome the obstacles are more likely to have offspring than the ones that don’t. There are four core concepts of Darwin´s theory of natural selection:

1. There is an overproduction of offspring in each generation
2. There is variation in features or traits within members of a generation
3. Individual differences are inherited from one generation to the next
4. Individuals with traits and features that fit well with the local environment are more likely to survive and have more offspring than the ones who don’t.

The genetic variability on which natural selection acts has two main sources:

• The reshuffling of genes that occur in sexual reproduction
• Mutations (errors that occasionally and unpredictably occur during DNA replication)

August Weismann established the doctrine of the separation of the germ (sex cells) and somatic (body cells) lines. What happens to the body cells during the life of an animal does not affect that animal’s gametes (egg and sperm).

Environmental changes spur evolution by promoting natural selection. Evolution can happen so quickly that people can see it happen. If the natural selection conditions are harsh, evolution speeds up, but complex changes take longer than simple changes such as the change of thickness of the beak of a bird.

There are three common mistakes regarding evolution:

1. Evolution has no foresight and does not move to a pre-determined plan
   There is no such thing as anticipating environmental changes. Only the immediate changes in the environment will make a difference in the natural selection and thus in the evolution.
2. Organisms can’t be ranked on an evolutionary scale
   This would mean that organisms move towards a planned end, which is not true. This means that humans are not further evolved than chimpanzees.
3. Natural selection is not a moral force
   There is no reason to call natural selection ‘good’ or ‘evil’. There is no moral ground for it. This is known as the naturalistic fallacy. Something is not good, because it is the way it is. It’s the same the other way around: something is not evil, because it is the way it is.

The mechanics underlying behaviour are products of natural selection. Functionalism refers to the attempt to explain behaviour in terms of what it accomplishes for the behaving individual. The functionalist’s approach explaining behaviour is the same as explaining anatomy. The functionalist believes that everything is to be seen in function: what does it accomplish for the individual; not only physical aspects but also behavioural aspects.

There are two kinds of explanations of behaviour in evolutionary terms:

1. Distal explanations (function)
   These are explanations at evolutionary level. They are statements of how the behaviour helped the individual’s ancestors genes make it to the next generation.
2. Proximate explanations (mechanism)
   These are explanations that are about the mechanism. They are statements of the immediate conditions; both inside and outside the animal, that bring on the behaviour.

Both these explanations are needed for the explanation of behaviour. It is needed to explain how come this behaviour is positive for the reproduction and what conditions bring out the behaviour, what’s the mechanism behind the behaviour.

There are four reasons why a trait or behaviour may not be functional.

1. Vestigial characteristics
   Some traits or behaviours could have been functional in the past but are not functional anymore.
2. Side effects
   Some traits or behaviours are the side-effects of natural selection for other traits.
3. Chance
   Some traits or behaviours result simply from chance. These variations are inconsequential for survival or reproduction, so they are not filtered out.
4. Traits or behaviours can’t always deal effectively with every situation
   Some traits of behaviours came into existence because they promoted survival and reproduction, but this does not mean that they always help survival and reproduction.

Species-typical behaviour are products of evolution, but that does not mean that they are necessarily rigid in form or uninfluenced by learning. Some species-specific behaviour is affected by learning: such as language and walking in young infants. It is species-specific behaviour to walk and talk, but it requires multiple hours of practice, so it is subject to learning and experience. Biological-preparedness is the manner in which an animal is physically prepared to perform a certain behaviour. Humans are well equipped to walk on two legs and they do it naturally, so they are biologically-prepared for it and it is species-specific behaviour. Dogs can walk on two legs, so they are (less) biologically-prepared for it, but it is not natural for them, so it is not species-specific behaviour for them.

Although species-specific behaviour is typical for species, it does require an impulse from the direct environment. Some sort of experience with the environment is always needed.

There are two conceptually different classes of similarity that exist across species.

1. Homology
   This is a similarity between two species that exist because of a common ancestor.
2. Analogy
   This is a similarity between two species that exist because of convergent evolution: two species have something in common (e.g: lifestyle, habitat) and independently develop a common characteristic.

Homologies are used for physiological research. A lot can be learned about physiological mechanisms regarding humans if we research another specie with a similar trait which happens to be a homology. Besides that, we can use homologies to research how certain animals evolved from simpler forms to the animals they are now.

Looking at analogies allows us to find out what may have caused the similarity between two species and what is the distant explanation of a certain behaviour, which could be for example the habitat or lifestyle.

There are four mating classes:

1. Polygyny (high female, low male investment)
   One male mates with more than one female
2. Polyandry (high male, low female investment)
   One female mates with more than one male
3. Monogamy (equal investment)
   One male mates with one female
4. Promiscuity (group investment, decreases violence -> paternal confusion)
   A group consisting of more than one male and one female mate with each other

In general, for species in which parental investment is inequal, the more parentally invested sex will be more vigorously competed for than the other and more discriminating than the other when choosing mates. This is Triver’s theory of parental investment.

Aggression is behaviour intended to harm another member of the same species. Most of the violence perpetrated by male primates has to do directly or indirectly with sex. Female primates do not only risk her life but also the offspring she’s nurturing because a female primate generally has a higher parental investment.

Helping can be defined as any behaviour that increases the survival chance or reproductive capacity of another individual. There are two categories of helping.

1. Cooperation
   This is helping another individual while also helping oneself.
2. Altruism
   This is helping another individual, while it decreases its survival chance or reproductive capacity.

The kin selection theory of altruism holds that behaviour that seems to be altruistic came about through natural selection because it preferentially helps close relatives, who are genetically most similar to the helper. The reciprocity theory of altruism holds that behaviours that seem altruistic are forms of long-term cooperation. If someone feeds another non-kin, that individual will be more likely to feed the one that’s fed him before if necessary.

There are two important fallacies:

1. Naturalistic fallacy
   This is the idea that because things happen in nature, they’re good and they’re supposed to be like that. “It is good to be selfish because it happens in nature as well” is an example of the naturalistic fallacy. Evolution is not a moral force and neither is natural selection.
2. Deterministic fallacy
   This is the assumption that genetic influences on our behaviour take the form of genetic control of our behaviour. This implies that the genes influence behaviour directly and not through the environment. This fallacy implies that genes control behaviour in ways that cannot be altered by environmental experiences or conscious decisions.