Levels and NS: Overview

Transcription

1 Levels and NS: Overview Levels of Analysis in Ethology Proximate Evolutionary (Ultimate) Natural Selection Darwin Natural Selection Tinbergen Darwin

2 Levels of Analysis in Ethology Ethology: the study of animal behavior Example: Why do male monkeys fight? Niko Tinbergen 1963 On Aims and Methods in Ethology Answer questions about WHY behaviors occur Four levels of analysis Proximate Causal Developmental Evolutionary Phylogenetic Functional Not mutually exclusive

3 Causal Behaviors brought on by cues in the immediate environment, including internal and external stimuli Sensory systems Neurobiology Hormones/pheromones Social cues Herring gulls Gelada baboon

4 Developmental Behaviors attributable to: Age/growth: physical/mental change and growth over the lifespan Experience/learning is a change in an animal's behavior in a particular situation attributable to its previous experience of the situation Young chimp learning to fish for termites from experience and observation Young human reaching the age and acquiring mental capacity and motor skills to do it myself

5 Developmental Harlowe s studies on rhesus social development Reared in cage alone Reared in cage with other monkeys

6 Proximate Levels of Analysis: Within a Lifetime Causal A behavior occurs because of a stimulus in the immediate (internal or external) environment during an organism s life (i.e., within a generation) Developmental A behavior occurs because of growth/ experience over an organism s life (i.e., within a generation)

7 Evolutionary Levels of Analysis: Over many generations of lifetimes Phylogenetic Level Understanding a behavior/trait by examining relationships with other species over evolutionary time Functional Level Understanding how a behavior/ trait was designed by natural selection to facilitate reproduction

8 Evolutionary history and relations to other species How does the behavior compare with similar behavior in related species? Why do birds sing? Because they evolved from reptilian ancestors who had throat pouches that could make vocalizations. Phylogenetic

9 Functional

10 Function Did the trait/behavior evolve? Did the trait/behavior impact the relative rate of reproduction of the animal s ancestors in the past? What did the trait/behavior do in the ancestral past, and how did that affect reproduction? What is the function of the trait/behavior?

11 Levels and NS: Overview Levels of Analysis in Ethology Proximate Evolutionary (Ultimate) Natural Selection Darwin Natural Selection Adaptation/Functionality Tinbergen Darwin

12 Darwin s Two Main Contributions Carried out the necessary research to conclusively document that evolution has occurred Discovered the process by which complex, functional design originates in living things: natural selection Charles Darwin ( )

13 Darwin s Life Family English moderately wealthy (mom was a Wedgewood) Dad influenced his career options Education Started in medicine at 16 Switched to theology at Cambridge Interested in the scientific ideas of geologist Adam Sedgwick and naturalist John Henslow At first, didn t believe evolution occurred Far more interested in biology than theology when he graduated

14 The Beagle Five-year voyage on the H.M.S. Beagle ( ) at age 22 with Captain Robert Fitzroy Galapagos Islands

15 Darwin s Influences Charles Lyell ( ): geologist who popularized uniformitarianism (vs. catastrophism )

16 Darwin s Influences Thomas Malthus ( ) was an economist who observed that more individuals are born than survive to reproduce; individuals are thus in a struggle for existence, that is, competition So, some individuals will reproduce, and others will not. Question: are winners a random selection, or do some individuals have an advantage over others?

17 Darwin s Influences One pair of mice is capable of producing a litter of six offspring as many as six times a year. Within six weeks, each offspring can produce litters of their own.

18 Darwin s Influences Artificial Selection

19 Darwin s Influences Comparative Anatomy Vertebrate forelimb

20 Darwin s Influences Fossils

21 Darwin s Influences Geographic distribution of traits: beaks were well-adapted to local environments on the islands

22 Adaptive Radiation in Galapagos Finches

23 Adaptive Radiation

24 Darwin s Influences Geology (Lyell) Within-species competition (Malthus) Artificial selection (breeders) Comparative anatomy Paleontology (fossils) Geographic distribution of traits (finches)...natural Selection

25 Darwin s Short Definition I have called this principle, by which each slight variation [in a trait], if useful, is preserved, by the term Natural Selection. - From The Origin of Species

26 Natural Selection 1. Reproducing entities exist.

27 Natural Selection 2. Variations exist, and they can be passed on to offspring (heritable variation).

28 Natural Selection 3. Variations have reproductive consequences.

29 Result: Natural Selection Occurs Over generations, the entire population will come to possess the reproductively advantageous variation.

30 After thousands of generations are acted upon by the physical process of natural selection, we get adaptations

31 Summary 1. Reproducing entities exist. 2. Heritable variations exist. 3. Variations have reproductive consequences. Result: natural selection occurs. the individuals which succeed in reproducing their kind will not be drawn at random from the population because selective pressures fall unequally on differently constituted individuals (Howard)

32 Dawkins Film First 30 minutes of Darwin, Life, and Everything (up to piano analogy scene) Next: variables, methods, science (set 4)

33 Darwin s Influences Why did he wait so long to publish his theory of natural selection? Alfred Russel Wallace ( )

34 Example: Finches at Daphne Major