Anth 2: Human Origins Science and April 1, 2021 First…Science What is Science?

• Science: • (from Latin scientia, meaning "knowledge") • a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the natural world

• i.e. method for explaining natural world Science Science is a method for testing hypotheses about the natural world • Hypotheses are proposed explanations for a narrow set of phenomena. These are not guesses. • You reject or fail to reject hypotheses Science neither proves nor disproves, but rather, narrows uncertainty Science is not

1. Complete 2. Absolute and unchanging 3. Untrustworthy because it changes 4. A mechanism for proving or disproving 5. Guesses 6. Disproof of God or any other belief system

These aspects of science may cause people who don’t understand the aspects to find science untrustworthy Scienctific Theories Theories are not guesses Accumulation of large data sets (tested hypotheses) can lead to the formation of theories • Theories are powerful explanations for a wide range of phenomena. Accepted theories are not tenuous. Even theories can be disproven, although this is very unlikely Limits of Science

Science can only help explain the physical/natural world. Limits of Science What is Evolution?

• Evolution is the change in allele frequencies that occurs over time within a population Clearing up misconceptions about evolution

• Evolution is not “just” a theory • Theories are supported by a body of evidence (tested and accepted hypotheses). • Evolution is a theory in the same way atomic theory is. Clearing up misconceptions about evolution • Humans did not evolve from chimpanzees • Humans share a common ancestor with chimpanzees. • Chimps are our closest living relative, not a direct ancestor. Clearing up misconceptions about evolution • Evolution does not have an agenda • Evolution has not determined the way species look or behave, it does not grant organisms what they need • It has provided ways of responding to the environment in particular ways Clearing up misconceptions about evolution

• Selection does not work for the good of the species • It operates on the level of the individual • Example • High- versus low-fecundity females • High fecundity favored even at species’ expense Clearing up misconceptions about evolution

• Evolution does not indicate progress • Evolution is a process of change, but that does not necessarily mean improvement History of Evolutionary Thought Before

• Common views: • Emerging scientific views: • Earth young (~6000y) • Earth old • Species divinely created • Earth’s surface has changed over time • Species immutable • Plants & animals have changed Man’s Place in Nature

Scala naturae (or Great Chain of Being): All of creation arranged hierarchically with humans (or God and his angels) at the top • Humans and animals separate • Fixity of species Hominins Hominins Hominins

Archea

Bacteria History of Evolutionary Thought • The 18th century, the age of reason • Interested in interpretation, relationships of different phenomena • Carl Linnaeus • Binomial nomenclature, Genus species • Jean-Baptise Lamarck • Inheritance of acquired characteristics History of Evolutionary Thought - Age of the Earth • (17th C): • based on the Bible • the earth is 6000 years old • there must have been many catastrophic events in order to explain how it reached its present shape in such a short time • scholars who disagreed were burned at the stake

• Charles Lyell and James Hutton • • the same physical laws that shape the Earth today also shaped it in the past, continuous and uniform processes • present features are the result of small, incremental changes Charles Darwin (1809-1882) Darwin’s Voyage on the HMS Beagle (1831) South America

Spent most of his time on land while the Beagle surveyed the coast

Observed geological as well as biological phenomena

First tidbits of evidence began to emerge – Megatherium in Patagonia The Galapagos Islands Finches - Variation Between and Within the Islands

• Why do the birds look different in different islands/habitats?

• How did this happen? By Means of (1859)

• Conflict with religious beliefs (including those of wife)

• Wanted to build a solid argument

• Catalyst: interactions with Alfred Russell Wallace From ‘The Origin of Species’ Why? - • Changes in physical structure, function, or behavior that allow an organism or species to survive and reproduce in a given environment. • Different animals are adapted to different environments • They do not adapt to their environment How? - Natural Selection • The process by which some organisms, with features that make them more adapted to the environment, preferentially survive and reproduce, thereby increasing the frequency of those features in the population. Example: Peppered Moths Natural Selection Crash Course Video

https://youtu.be/aTftyFboC_M Darwin’s Postulates of Natural Selection

1. There is a struggle for existence. • (i.e. there are more born than will survive)

2. There is variation in features related to survival and reproduction. • (i.e. we are all different)

3. This variation is passed from generation to generation. • (i.e. differences are heritable)

These three postulates make evolution by means of natural selection inevitable. An Example of by Natural Selection

Daphne Major island, in 1976 (a) and 1978 (b), before and after a severe drought, during which only hard seeds were left

Medium ground finch Example of Adaptation by Natural Selection: Examine the Postulates

1. There is a struggle for existence.

2. There is variation in features related to survival and reproduction.

3. This variation is passed from generation to generation. Postulate 1: Struggle for Existence

• Decrease in seed availability • 1,200 birds reduced to 180 Postulate 2: Variation

• Beak depth varied • Influenced survival Postulate 3: Heritability

• Beak depth passed from parent to offspring Evolution! The Process of Change Over Time

Species are dynamic, changing populations of individuals Stabilizing Selection

• If its good to have a deep beak, why aren’t all beaks deeper?

• Beaks that are too deep are disadvantageous to juveniles Individuals Don’t Evolve, Populations Do

But Natural selection acts on the individual Populations evolve! Selection Is Not Directional • Over time, beak size fluctuates according to environmental conditions and natural selection • There is no direction to select or end goal of evolution Evolution ≠

Evolution can lead to speciation, but that’s not the definition *speciation: formation of a new species Reconciling Seemingly Deleterious Traits With Natural Selection

• Relates to struggle for existence. • the goal of existence is to reproduce (at least from your genes’ point of view)

• Natural selection is not the only force acting on individuals: Sexual Selection

Leads to changes in frequency of those traits that are either attractive to members of the opposite sex or helpful in competition with members of the same sex. Types of Sexual Selection

• Intrasexual (=within sex): favors the ability of one sex to compete directly with one another for fertilizations, for example by fighting • usually takes the form of male-male competition Types of Sexual Selection

Intersexual (= between sexes) 1. Mate conflict occurs when the genetic/reproductive interests of females and males diverge 2. Mate choice favors traits that attract the opposite sex (usually female choice) Types of Sexual Selection Intersexual (= between sexes) Mate conflict occurs when the genetic/reproductive interests of females and males diverge • can lead to either one sex having the advantage or to an arm’s race between the sexes • can be mechanical or behavioral

Bed bug males practicing ‘traumatic insemination’

Mate Choice Females are attracted to traits that indicate: 1. Direct material benefits: e.g. access to resources, protection from aggression, investment in her and her offspring Mate Choice Females are attracted to traits that indicate: 2. Indirect benefits: • good genes, as indicated, for example, by the fact that the male can survive despite possessing the attractive trait (handicap hypothesis) • good genes, reflected in the trait (honest signal hypothesis) – traits often display fitness of male (e.g. parasite load, testosterone levels) in a way that is impossible to fake – some overlap with handicap hypothesis Mate Choice

Females are attracted to traits that indicate: 3. Nothing: arbitrary, nonadaptive traits (but possessing them will make the offspring more attractive?) • Thought to evolve through runaway selection, where traits and the preference for those traits coevolve together

Proboscis monkey Sexual Selection and Sexual Dimorphism

• Sexual dimorphism = difference between the sexes in some trait • Usually due to sexual selection • Body and canine size most common, due to intrasexual male-male competition • More common when trait is maladaptive or is honest signal of testosterone levels How Do Complex Structures Arise? Evidence for the Evolution of the

• Intermediate steps: living mollusks show steps in eye evolution (intermediate steps are still adaptive)

Evolution is a tinkerer, not a designer!

How Are Traits Passed Between Generations?

• Relates to third postulate: traits must be heritable!

• In Darwin’s time, people (including Darwin) believed in (traits of parents blend in the offspring) • BUT everyone would look the same after several generations, where does variation go?… How Is Variation Created/Maintained?

• Relates to second postulate: there must be variation in a trait for natural selection to act

• How is variation maintained if natural selection eliminates it? • Where do novel forms come from if not already present in original population?