Listen to part of a lecture in a psychology class. Okay, today we're starting our unit on developmental psychology. And to give you an overview, I'm going to go over some of the principles of development that you'll be reading about in the next few weeks. now, first, when I say development, remember I'm talking about human development, the physical, intellectual, and personality changes that occur from birth to uh, around age 16 or so. the first general principle is that development is influenced by both heredity and environment. Now, who can give me an example of how heredity, what we inherit genetically from our parents influences development appearance. I mean like children properly look like their parents because of their genes. right? Yes. For example, your physical size, hide and so on is partly determined by heredity. if both your parents are tall, it's likely you'll be told to write. but physical size is also determined by your environment. for example, suppose with your parents were quite tall. And assuming you get all the right nutrients in your diet while you're an infant, you're likely to grow tall too. but if you don't, you may not grow so tall, since good nutrition is important for growing bones. now, while it's clear that both factors contribute to development, what's not so clear is the extent to which each factor contributes a yes, Jeanne. I wonder if there have been studies to find out. What's more important. I mean, like, you know, does heredity have a bigger influence than environment, or vice versa? in fact, there have been several studies on the relative influence of heredity and environment, but they've been largely inconclusive. Since these two factors are extremely difficult to separate, especially with regard to their influence on intellectual development, we cannot isolate the influence of each factor. so for now, let let's just say that development is influenced by both heredity and environment. tanned in our upcoming readings and discussions will be dealing more with the complex interplay of those two factors. ok, now, the second principle is that development takes place at different rates for different parts. now, do I mean that your left foot will grow very quickly for a while, and then your right foot will grow slowly, and then your arms will grow one after the other? earl, like me at about 12 years old. no, seriously, that's how I felt when I was 12 or 13. yeah, yes. Well, sometimes during adolescence, when when children are growing so quickly, it may seem like that when children feel awkward and clumsy. but what I meant to say is that physical growth as a whole may proceed at a different rate from, say, mental development. So for example, you might see an 11 or 13 year old adolescent who looks quite mature, almost like an adult, but who's clearly still behaving like a child. that's because abilities like cognition and perception may develop at different rates and reach their maximum development at different times. ok, for principal number three, now you may already know that there are specific stages in an infant development. Uh, for example, infants can lift their chin before they can sit up. And if you watch toddlers, older babies, you know, they can stick before they can stand, uh, stand before they couldn't crawl. all crawl before they can walk. yes, exactly. That's because development follows in orderly sequence. Now, while sequential development, uh, the order in which children reach developmental stages is pretty clear. For physical development, uh, specifically motor development, as we just saw, it's not so clear for intellectual development. it's pretty easy to tell whether a child is at the crawling stage or the walking stage. But it's not so easy to identify what stage of intellectual development a child may be at, since you can't get inside the child's brain and see what they're thinking. there's still an orderly sequence. It's just that the sequence to intellectual development is less obvious, and the stages are less distinct. and that takes us to the next principle. that. development is continuous. stages of development are not completely separate from each other. There's no clear cut break between the starting point of one stage and the completion of the next. so you can see how these changes could easily go unnoticed by child's parents. but what about all these charts? You see in child development books? You know, the ones that show separate stages and when they happen. well, if you look again at those charts, you'll probably notice that the age is never exact. it's always stated as a range of months or years. that's because it's impossible to be exact about when a specific stage of development occurs. the last principle I want to talk about, and this one you've probably noticed yourself, concerns the variability in individuals development, which simply means that we don't all develop in the same way.