x: [[Evolutionary Psychology]] Tags: # Evolution of The Brain and Behavior ==Homoplasy== is a resemblance between behavioral or physical characteristics because of convergent evolution. ==Homology== is resemblance between behavioral or physical characteristics due to similar ancestry. ==Analogy== is resemblance between behavioral or physical characteristics due to similar function. ## How do Biologists Classify Things? 1 Biologists classify things according to their kingdom, phylum, class, order, family, genus, and species. A helpful mnemonic to memorize this is to =="kindly put clothes on, for goodness sake."== ![[Pasted image 20220908094930.png]] The genus is always capitalized and both the species and genus are italicized. #### How is Speciation continuous? 3 Often people assume that species are categorical. But in reality, the scheme is ==continuous==. There is no defining point in which a new species is formed. It's a gradual process. ## Why Study Other Species? 3 Studying other species can give us insight into how our own bodies work because species often evolve similar adaptations for the same environment. For the most part the brains of humans in comparison to other mammalian species differ from a size standpoint. Of course there are variations between species but this is largely why studies on other species brains can give us insight into the way our own brain functions. ### What ocean species has been invaluable to study for insight into learning and memory? For example, the Apylasia snale is one of the animals that has given tremendous insight on learning and memory because it has a quiet simple nervous system with only 20,000 neurons. And parts of the snale can survive for days when cut out just by putting seawater with the right ions over it. ###### What three ways has apylasia been shown to learn? [[Memory and learning in neuroscience]] 1. Habituation: learning to stop responding as much to the same stimulus. 2. Sensitization: learning to make larger responses from the same stimulus. 3. Dishabituation: learning to revert a habituation ###### How does the apylasia show habituation to touch? Researchers who touch the gill or other external organs in some way, showed that over time with more and more touches the apylasia won't retract the gills as long. ![[Pasted image 20221118103824.png]] ###### Why does habituation occur in terms of neurotransmitter release? The same touch stimulus releases less glutamate neurotransmitter therefore causing less action potentials and less of a response. #### What does the size of the brain correspond to? 3 In general, the size of the brain region corresponds to the importance of that function in the species that evolved to have it. For example, rats have a very small region of their brain devoted to sight because they are mostly nocturnal and live in the dark in comparison to squirrels. Another example comes from birds that hide and store food for later use. Usually hippocampus size corresponds to animal size. However, in birds that store and hide food, their [[Hippocampus]] is much larger than normal because they must remember where they hid their food. Here we can see the evolution of the family tree of mammalian brains: ![[Pasted image 20220908095411.png]] ### Which Species is the Brainiest? 3 Of course, the obvious next question neuroscientists had to ask was which species has the biggest brain to body size ratio? After studying a variety of different species as big as the blue whale to the modern day shrew, scientists graphed the ratios. They created a line of best fit. The distance that a species brain size to body ratio is above or below the line is k and called the ==encephalization factor.== What do you know, among primates the encephalization factor is largest for humans. ![[Pasted image 20220908100646.png]] ## Why Did We Evolve to Have Such Large Brains? 3 There are three main theories for why humans evolved to have such large brains in comparison to other species. ### Tool Use Some groups of scientists believe we evolved big brains so that we could fill the ecological niche of tool use. There are fossil records supporting the idea that we might have used tools to break into the bones of eaten corpses to get at the bone marrow. ### The Social Brain Hypothesis The [[Social Brain Hypothesis]] postulates that a larger brain is needed to handle the cognitive load of interacting socially with so many other humans. Many studies have been done to try and show there seems to be a limit to the number of social relationships we can feasibly maintain. [[Dunbar's number]] as it is called states we can only reasonably maintain around 150 social relationships. There seems to be a lot of evidence supporting this hypothesis. Human babies are born remarkably weak and underdeveloped in comparison with some other animals. They need to be raised for years before they can viably make it on their own. This means they have to have the brains to learn from their caretakers. This hypothesis is supported by Herman Potzner in his book [[Burn]] where he explains humans rose to the top largely because of their capacity for sharing food with other apes. Unlike our ape ancestors, we regularly share food with others in our tribe. Sharing a meal with someone is one of the most sacred acts of bonding there is. Getting meat requires a great deal of physical activity to do. Our ancestors needed to be sure if they went out on a meat search and came back empty handed, they wouldn't go hungry. By having the women stay back and forage for food they could share with everyone, men could risk going out and looking for meat. Plus, if they did find a big catch, everyone in the tribe could feast. ### To Adapt to New Environments Other scientists believe we evolved big brains to help us learn to adapt to new environments we travelled to. Ancient humans had to memorize thousands of different plant and animal species as well as countless other things to survive well in their environment. We were opportunistic omnivores eating whatever we could manage to get our hands on. To support the insane amount of learning we needed to do this we evolved bigger brains. ### To Attract Sexual Mates The last theory for why we evolved massive brains is because it allows us to do more elaborate behaviors that can attract mates. This is the theory most supported by rich but controversial field of [[Evolutionary Psychology]]. #### How did humans evolve to have such large brains? Perhaps the better question to ask is not why humans evolved but how they managed to afford evolving such expensive biological machinery in the first place (see: [[Human beings rose to the top of the food chain by sharing food]]). ### Evolution is now broken 3 Because of the society we live in today humans have created an environment where natural selection doesn't work like it normally does. Humans are no longer evolving like we used to. Instead we are living in a modern world with ancient brains. I argue in my book summary of [[What We Can Learn From Our Past Sapiens By Yuval Noah Harari]] that this has led to a lot of problems.