Lecture 3 - Biology.pdf

Lecture 3 - Biology Overview 1. Why brain development is important to developmental psychology 2. Evolution and why it matters that we are like our parents 3. Molecular biology - the essential bits 4. Heritability - really understanding the nature/ nurture debate in developmental psychology Brain D...

Lecture 3 - Biology Overview 1. Why brain development is important to developmental psychology 2. Evolution and why it matters that we are like our parents 3. Molecular biology - the essential bits 4. Heritability - really understanding the nature/ nurture debate in developmental psychology Brain Development You are your brain Your psychology is the product of a set of biological processes These processes run through interacting networks in your brain Ultimately, all your feeling, thinking and behaviour can be explained in terms of what happens in these brain networks What About Developmental Psychology? A big question for developmental psychologists is What is the role of brain development in psychological development? Does brain development drive the changes we see in children’s emotion, thinking and behaviour? What is brain development like… Broadly, we can distinguish between pre-natal and post-natal development Piaget was Wrong The problem for Piaget’s theory is the evidence The brain is not switched-off before birth - but pre-natal effects are limited More importantly, the post-natal brain develops a lot more than a superficial look would sugget The brain doesn’t just get bigger - it changes in many ways 1) Synapse Density Brain has about 86,000,000,000 nerve cells or neurons (Herculano-Houzel, 2012) The pattern of connection of these neutrons makes everything you are psychologically speaking This pattern changes during development 2) Long Range Connectivity Synapse are about local connections - long range connections are also very important Because brain function depends on forming long range connections which create brain networks Speech depends on the connection of many parts of the brain Connectivity changes Post-Natal Brain Development To understand psychological development, we need to understand postnatal brain development Above all, how the two kinds of development interact over time Mark Johnson wrote the first textbook on developmental neuroscience Suggested three ways brain development could lead to cognitive development Three Accounts - Inhibitory Examples 1. Maturational account suggests brain activity becomes focused in the right place 1. For inhibition - increased activity in the IFG during development (Smith et al., 2017) 2. Interactive specialisation account suggests what develops is the co-ordination of brain networks 1. Better coordination of IFG-basal ganglia-thalamus during development (Ruby et al., 2007) 3. Skill learning - executive function needed to learn skill - but activity reduces when skill learnt 1. Talked about for inhibition, but no experiments yet (Simpson & Carroll, 2019) Evolution Natural Selection Natural selection relies on four things: 1. There are differences between individuals within a species = traits 2. These traits are passed onto offspring 3. Some traits are ‘fitter’ than others (fitter means more healthy offspring) 4. Excess of individuals If these four things are true, then: Fit traits must spread between generations Species must become fitter over time Evolution must happen Monogenic Traits Evolution requires a mechanism of inheritance A theory was developed at the beginning of the 1900s by Bateson and some other biologists One of the most powerful ideas in science Unit of inheritance = “gene”, different versions of a gene = “alleles” How you express a trait depends on the specific alleles that you carry Originally assumed: Monogenic trait = a single gene determines a specific trait All Psychological Traits are Polygenic Psychological traits are the most polygenic of all = The product of many many genes with each gene having a very small effect How many genes - well, how many have we got? Humans have about 20,000 (traditional) genes More than half (~55%) are expressed in the brain Each has some effect on every psychological trait No single genes “accounts” for >1-2% of any trait ** Lots of genes with Tiny Effects ** DNA DNA and Inheritance Unit and Inheritance = “gene” Genes are made out of DNA - DNA is the heritable material in almost all life DNA has a four-letter code - A T G C - and comes in a double strand As pairs with Ts, Gs pair with Cs. DNA Makes Proteins Makes Us How does DNA make your body? DNA codes for proteins Proteins control development before/ after birth Proteins make up a lot of the physical structures in your body Protein also run most of the metabolic processes that you need to live In terms of your biology, you are the product of your DNA, because you are the product of your proteins Proteins are made from amino acids - 20 kinds If one letter of the DNA corresponded to one amino acid - DNA could only code for four amino acids From two consecutive letters - you get 4x4 or 16 amino acids So it takes three DNA letters to specify all amino acids = Codon A mutation can change a letter in the DNA and so change an amino acid in a protein DNA and Genes The 1900s definition of a gene was “a unit of inheritance” Discoveries in the 1950/60s changed that definition: A gene is a sequence of DNA that codes for a protein Reading the human DNA sequence (a genome) began in 1990 Human Genome Project was completed in 2003 Humans have 20,000 genes making 20,000 proteins Different alleles have difference DNA sequences and make different versions of the protein From DNA to Chromosomes Proteins called “Histones” Form into a ball - and the DNA raps about it Then the balls form a fibre = mix of protein and DNA The fibre forms into loops and these loops form into bigger loops These are packed together into a chromosome Human Chromosomes In all eukaryotes, DNA is split over a number of chromosomes Each species has a distinctive set of chromosomes Human’s have 46 chromosomes - this is a simplified representation of them The chromosomes come in pairs - one from each of your (biological) parents 22 pairs are identical in all of us The 23rd pair is different - these are the sex chromosomes Heritability The Traditional Nature-Nurture Debate Traditionally two proposals have been made to explain how humans develop: nature/ nurture Both genes and environment can influence a trait Heritability measures influence of genes on a trait Heritability is the proportion of the total variation in a population that is due to variation in genes So, it runs from… 0% heritability 100% heritability is all genes and no environment Why is Heritability Misunderstood? In a population, it measures how much variability in a trait is due to variability in genes: If there is very little variability in genes, then the heritability will be low Even if genes have tight control over the trait Heritability is not fixed, even though your genes are - because it’s only part of the story If the environment varies in a new way, then it is possible for heritability to reduce “Psychological” Heritability is High Heritability starts to be measured in the 1980s The best way of doing this is through twin studies How much more alike are monozygotic twins than dizygotic twins? The results were surprising… Heritability of lots of psychological traits is high - 50 to 60% is common (common cancers are 10-20%) Intelligence, some aspects of personality and many kinds of mental illness Some psychological traits have lower heritability Why so Polygenic? For evolving humans, being psychologically-able was under the strongest selection pressure This makes psychological traits very polygenic Traits under the strongest selection - pull in genes to improve fitness (survival + offspring) If something’s critical to a species fitness, lots of genes are going to end up trying to make it better The Watershed Model Theory that traits under intense selection use many genes Their analogy is that lots of small processes feed into a big outcome (Cannon & Keller, 2005) Any psychological trait depends on hundreds of different biological processes and thousands of different genes So, biology matters in psychology Conclusions Psychology is the product of the brain, which in turn is the product of evolution Brain development and psychological development interact through life Thousands of genes each with tiny effects influence our psychology - this means that… Heritability is high But genes do not determine our psychology - because they act with the environment #PS406