1. 3/21/01 Models of genetic and cultural evolution, part 2 College 002: Biology, Language, Culture Thursday, April 3, 2001

2. 3/21/01 Modes of genetic change Darwin 1: Random genetic variation + natural selection = adaptation “survival of the fittest’ Example: food preferences (chemotaxis etc.) Darwin 2: Random genetic variation + sexual selection = ? “Survival of the sexiest” Examples: size, symmetry, ornamentation may be environmentally adaptive or not “runaway sexual selection” Genetic drift: Random genetic variation + random events = random change Example: “molecular clocks” Other?

3. 3/21/01 Genetic adaptation as learning Advantages –Application of learning is fast “instincts” available from birth –Happens anyhow preferences & behaviors have genetic aspects natural & sexual selection always operate Disadvantages –Rate of learning is slow one “trial” per generation –Individuals are inflexible –“Trial and error” is the only method Better if individuals also learn from experience –adjust behavior depending on environment biochemical learning neural learing in higher animals –always partnership between genetic & individual learning

4. 3/21/01 Example: food choice Types of sensory input –chemical, optical, acoustic, etc. Types of response –attraction/avoidance –feeding Strong genetic component –innate chemical preferences from bacteria to humans BUT individual learning applies as well –ubiquitous in higher animals Also social learning

5. 3/21/01 Food preferences in slugs Limax species eat a wide range of plants. Associated chemicals naturally attract them and stimulate feeding behavior. However, many plants are toxic to slugs, who have a complex system for learning which plants to avoid.

6. 3/21/01 Slug lip/brain can “learn” The isolated lips and nervous system of the terrestrial slug Limax maximus will produce some of the feeding behavior of the intact animal; i.e., they generate the rhythmic neural activity characteristic of ingestion in response to food extracts applied to the lips. This preparation will respond to a variety of food extracts that elicit feeding in the whole animal. This provides the opportunity for aversive conditioning experiments involving taste discrimination. Pairing lip chemostimulation by attractive food extracts with lip chemostimulation by using bitte plant secondary substances can cause the isolatd brain to selectively suppress its neural response to one food extract while remaining responsive to another. Chang & Gelperin 1980

7. 3/21/01 Experimental results Quick learning from bad experiences –sickness (e.g. from CO2 poisoning) –associations of chemicals One-trial learning –on first exposure to the plant type –like “bait aversion” in rats Generalization from “taste” to “smell” –Different organs (tentacles vs. lips) Obvious advantages over purely genetic food preferences –“flexible instinct”: a specialized learning system –advantage in “arms race” with plants relative investment in toxins depends on predation

8. 3/21/01 From individual to social learning Some problems of individual learning 1.It’s hard to learn from a fatal mistake 2.Some crucial skills are not obvious 3.Distribution of resources in space/time is often complex and locally variable Social learning can be helpful 1.Learn from the fatal mistakes of others 2.Easier to imitate than invent 3.Knowledge about resources can accumulate

9. 3/21/01 Social learning in bears A mother brown bear teaches her cubs to fish. Brown bear cubs stay with their mother for 2-3 years, The survival of brown bear cubs is totally dependent on the skill of the mother in both protecting them and teaching them the basics of what to eat, where when and how to get it, where to den, and how to cope with danger. Fewer than 50% survive to become independent adults

10. 3/21/01 Brown bear diet (Glacier Park) In different places and times, crucial parts of bear diet can be from whitebark pine seeds (harvested from squirrel middens), cutworm moths (as many as 40,000 moths per day), berries, roots, …

11. 3/21/01 Learning/culture as evolution Random behavioral variation + reinforcement –analogous to Darwinian natural selection operating on stimulus/response associations rather than on genes Imitation of attractive models –analogous to Darwinian sexual selection may or may not be environmentally adaptive “Memetics” –Ideas (“memes”) as analogous to genes –Culture as the “meme pool”

12. 3/21/01 Limitations of the analogy Genetic evolution has a consistent physical foundation, while learning and culture do not –genes “exist”, memes don’t Culture is subject to a wider set of dynamic forces than the gene pool is –for example, conformity

13. 3/21/01 Physical foundations –DNA/RNA/protein system exists Genes are identifiable, replicating units Same mechanisms from bacteria to humans –Physical substrate for individual and social learning is highly variable Many specialized subsystems –e.g. food preferences vs. face recognition Basic units (“ontology”) not well defined –across different systems –at all?

14. 3/21/01 Dynamic forces Forces in genetic evolution –random mutation (accessible genotypes) –natural selection (survival) –sexual selection (reproductive efficiency) –that’s all! Other forces in “memetic” evolution –non-random new ideas e.g. analogy –higher-level influences on selection e.g. conformity

15. 3/21/01 Language as species (to be continued…)