1. EARLY HUMANS An Evolutionary Perspective
AP HG
Mr. Hensley
SRMHS
Today the goal is to look at a few simple rules that govern all living things (natural selection sexual selection and inclusive fitness. Once we understand those rules, we’ll look at how those rules shape adaptations – adaptations that can be primary, secondary or simply random. Finally, we’ll apply these biological rules to aspects of human culture and cultural norms, especially cultural beliefs that are universal. This process is called “evolutionary psychology”.

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
The adaptations we carry with us helped us first survive an often hostile environment. But also, some adaptations helped us reproduce more effectively. Both survival and reproduction are needed to ensure the continuation of the human race – survival alone is not enough, reproduction alone is not enough. Both are required. This needed combination is often overlooked – as is also the fact that adaptations that help us survive and reproduce but then carry negative consequences in old age (say, male pattern baldness) would still be passed on.

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
Natural selection is the main motor behind evolution. As seen in the simple drawing here – some environmental factor kills off low shrubs leaving only tall trees. Animals with short necks now do not carry a successful adaptation – but those animals with long necks do have a successful adaptation. They thrive, the short-necks die and after several generations, a new species of long-necked animals (giraffes) is added to the diversity of life on the planet.

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
Evolutionary processes are difficult to see because they operate over vast stretches of time – time spans that are truly beyond human comprehension. Humans themselves have used natural selection (well, to be specific – unnatural, human-driven selection) to modify and change plants and animals. Think of how humans gradually developed corn from a native grass called teosinte. Or how both the Chihuahua and the Great Dane come from the same root animal, which resembles a wolf.

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
Reproduction is the other motor driving the selection process. Adaptations that improve the ability of an organism to mate and reproduce will be passed on to future generations even if those adaptations are working against long-term survival. An adaptation that results in lots of reproductive success but actually lowers life expectancy will still get passed on because at the level of the gene, reproductive success is all that matters. The peacock’s tail is the obvious example, as are giant antlers on the heads of stags.

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
Adaptations can arise because they make you better at attracting mates (once again, the peacock’s tail) – this is called intersexual competition. Or adaptations can be passed on because they make you better at beating out others for access to mates, which is called intrasexual competition. Here, the best example would be he antlers of the male deer. Human examples of intersexual competition include longer hair for women and female body shape. For intrasexual competition, young men are exceptionally predisposed towards violence, usually towards other young men.

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
One final driver of evolution is the idea of inclusive fitness. At the genetic level, an adaptation that doesn’t help my reproductive or survival success but does positively impact the survival of my close genetic relatives will get passed on to future generations. Society and culture are possible evolutionary adaptations that occur because they contribute to inclusive fitness.

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
Not everything is a primary adaptation to a survival or reproduction problem. Some adaptations are by-products of larger ones. We think that hair length on women is a sexually-selected primary adaptation. Whether long female hair is straight or curly is probably an incidental by-product. If the genes that control longer hair in women are also responsible for (say) earlobe shape, then earlobe shape would be a type of incidental “tag-a-long”. We get the incidental by-product to gain the very beneficial primary adaptation.

10. Culture is an Adaptation
Humans can pass on adaptive behaviors through culture which is 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?
As mentioned earlier, families and societies can lead to greater inclusive fitness. Humans use culture (a set of shared beliefs or values) to pass on adaptive behaviors from one generation to the next. Cultural universals – behaviors common to all cultures – are excellent candidates to be looked at as adaptive problem solvers. Religion is such a cultural universal. Why is it so common? It does do an excellent job of ensuring cooperation and group cohesion as group sizes get large. There are obviously intergroup conflict potentials – one religious group trying to destroy another – but the intragroup benefits of religion are significant.

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?
As we saw with inclusive fitness, altruism should follow lines of genetic relatedness. I’m more willing to sacrifice myself to save my son than I would be to sacrifice myself to save my second cousin.

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
Every successful act of adultery requires both a female and a male partner – but do the two sexes have the same tradeoffs? The same rewards? Are they solving the same problems? Male adultery is straightforward – male adulterers are rewarded by seeing the near-limitless spread of their genes through a near-limitless number of potential children. This, by the way, is called an “R” reproductive strategy – have as many offspring as possible, hoping that there is strength in numbers and that a few of them will survive. But women employ “K” strategies – lavish all your resources on a few children to guarantee them the best chance of survival. Why would a woman commit adultery and run the risk of alienating her spouse and losing his support for her children?

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
Two theories attempt to explain female adultery, each has its own strengths and weaknesses. The Resource Theory says that women cheat so that they can access resources from multiple men. More resources means more survival success for their offspring. A second theory says that female adultery is driven by a desire to engage in mate switching, that adulterous women are “kicking the tires” of potential new mates after their current mate fails to provide.

14. Resources or Reproduction?
Here we see mate age preferences for men and women. Women prefer men the same age or a little older while men… well, men prefer young women no matter how old they are. This is solid evidence that women view sex as a way to gain resources for their children (K strategy) while men use sex to maximize their number of potential children (R strategy).

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
Jealousy also has a sexually differentiated aspect. Studies show that men are far more concerned about sexual infidelity while women care more about deep emotional attachments (an “emotional affair”). This difference would be consistent with the idea that men engage in an R strategy (maximize the number of offspring) while women engage in K strategies (maximize the amount of resources directed at a few children). In patriarchal cultures, where men control the society, institutions and customs are in place to prohibit sexual infidelity, up to and including truly ghastly things like female circumcision.

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
Homosexuality is a human universal – it exists in all cultures. Current science also indicates that it is genetic and not a “lifestyle choice”. Of course, by definition, it results in zero reproductive success. Why then is it universal? Again, two theories attempt to explain it. The first says that homosexuality is a by-product of hyper-heterosexuality. By this I mean that a set of genes that normally result in robust heterosexual behaviors can sometimes carry the genes that can cause homosexuality. If there are five sons and four carry the hyper-hetero genes while only one is homosexual, then the overall reproductive success of the four sons with the hyper-hetero adaptation will outweigh the lack of reproductive success of the homosexual brother. The second theory applies the concept of inclusive fitness – the occasional homosexual sibling will still be part of the family and still help raise children and provide resources, making the family unit stronger.

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
Practitioners of the evolutionary perspective often fall prey to the teleological fallacy, the belief that evolution is proceeding along some preordained path to a predetermined conclusion. This is sometime referred to as “progressivism”. Evolution should not be anthropomorphized. It is a process, not a sentient being. Any adaptation that is beneficial will be passed along, no matter what direction it moves us in. As for “just so” stories, it can be tempting to start at the end of the evolutionary process and then attempt to reason backward. We evolved a fear of spiders to protect us from the danger of spider bites. Sounds good, right? But spiders have never posed a great threat to humankind, in modern or ancestral conditions. More likely, we have devloped an understandable aversion to the fast, unpredictable motions that spiders tend to make.