EARLY HUMANS An Evolutionary Perspective

1. EARLY HUMANSAn Evolutionary Perspective AP HG Mr. Hensley SRMHS

2. Evolutionary Perspective • All humans today come from an unbroken line of ancestors who accomplished two tasks: They survived to reproductive age, and they reproduced • We carry adaptive mechanisms that led to our ancestors’success

3. Natural Selection • Changes that better enabled an organism to survive and reproduce lead to more descendants • Descendants inherit the changes that led to their ancestors’ success • Thus, successful variants are selected and unsuccessful variants are weeded out • Over time, successful variants come to characterize entire species

4. Over Time • Your lifetime will max out at about 100 years • Complex life has existed on Earth for 5 million of your lifetimes • Evolutionary changes occur over geologic timescales – they are imperceptible to time at the human scale

5. Survive AND Reproduce • Darwin noticed that many mechanisms seemed to threaten survival, such as the peacocks tail • Darwin proposed evolution by sexual selection —these traits evolved because they contributed to mating success

6. Two Types of Sexual Selection Intrasexual competition: Members of the same sex compete with each other for sexual access to members of the other sex Intersexual competition: Members of one sex choose a mate based on their preferences for particular qualities in that mate

7. Age and Homicide Rates

8. One More: Inclusive Fitness • Inclusive fitness refers to both your personal reproductive success (number of offspring you produce) plus the effects you have on the reproduction of your genetic relatives, weighted by genetic relatedness • Explains families

9. Not Everything is An Adaptation • Adaptations (primary product): hairlessness • Byproducts (incidental): curly or straight hair • Sometimes things are genetic “tag-alongs” – like nipples on men • To get the beneficial adaptation, we take the neutral byproduct

10. Culture is an Adaptation • Humans can pass on adaptive behaviors through culture whichis a set of beliefs and norms passed from one generation to the next • Ex: religion – every culture has one but WHY? • What adaptive problem does religion solve? • Are their trade-offs? • Do the benefits exceed the costs?

11. Altruism? • Would you sacrifice your life to save a stranger? • Other choices: son versus nephew? • Daughter versus son? • Spouse versus child? • Teenage daughter versus infant daughter? • Is there a (hint: genetic) pattern to your answers?

12. Adultery: Why Would SHE? • Adultery makes sense for men (sexual selection rewards successful adulterers) • Why would a woman cheat? Where is the benefit? • Men and women face different adaptive problems • Men – only reproduction • Women – resources to raise their children • K versus R strategies

13. Adultery: Three Theories • Increased Access to Resources through Confusion of Paternity or increased social standing because of behaviors or extra protection from multiple men • Mate switching: the short-term encounters are a way to force mate switching if current mate fails to protect, or to provide resources • Done for evaluation purposes – women engage in short-term mating to “kick the tires” of a potential long-term mate

14. Resources or Reproduction?

15. Look at Jealousy • Men need to be certain of paternity • Women need resources to raise their children • Prediction: men will get more upset at sexual infidelity; women will be more upset about emotional infidelity • Confirmed across cultures

16. Homosexuality is Universal • How can homosexuality be an adaptive trait? • One theory: it is an occasional byproduct of hyper-successful heterosexual traits (over multiple sons, the benefits outweigh the costs) • Another idea: it increases inclusive fitness of a family

17. Dangers of the Perspective • Avoid teleology – the belief that nature progresses towards some sort of predetermined outcome or goal • Avoid “just-so” stories – just because it sounds good, you still need evidence