Exam 2

Ontogenetic isometric scaling

young of a particular organism are basically miniatures of adults

Precocial young

eyes open, maybe feeds itself, walks soon after birth

external work

-work done to move the whole body
-stays the same with increased speed
-forces on the ground

internal work

-work to swing limbs back and forth because the limbs themselves have mass
-forces applied to limbs
-increases with increased speed

Rotational inertia

- I\=mr^2
-shape matters

In geometrically similar animals, angular acceleration scales to...

-body mass to the -2/3 power
-as an animal becomes larger the angular acceleration decreases

Long leg functional tradeoff

-long legs increase locomotor economy by reducing
1. the number of times muscles have to turn on to traverse a given distance
2. the peak forces to walk or run at a given speed
3. the speed at which muscles must generate force
-long legs reduce locomotor economy by increasing rotational inertia of the swinging leg which increases internal work of locomotion

What do animals do to compensate for this long leg functional tradeoff

-reduce amount of muscles distally
-loss of digits
-overal reducing mass distally

correlation between fierceness of mom and k-selection

-k selection: few children, high investment
-moms are more fierce when they have less children

r/K selection theory

relates to the trade off between quantity and quality of offspring

K selection species

invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood

Altricial

-species in which the young are incapable of moving around on their own soon after hatching or being born. They are dependent on their parents.
-humans are the most k selected and most altricial species on the planet

Observation 1 of humans being the most k selected and altricial people

-no other female invests more in individual offspring
-yet no other great ape is as physically weak

Observation 2 of humans being the most k selected and altricial people

humans are unusual mammals, unusual great apes, because humans have paternal investment

Observation 3 of humans being the most k selected and altricial people

postmenopausal lifespan (grandmothers)

Observation 4 of humans being the most k selected and altricial people

male choice

Observation 5 of humans being the most k selected and altricial people

-helpers at the nest (alloparenting)
-cooperation to raise, protect, and educate

Contest competition

in species in which males compete by fighting, females appear to prefer traits that enhance fighting performance

Two hypotheses of the functional basis of human sexual dimorphism in strength

1. division of labor associated with foraging subsistence
2. male-male contest competition

Division of labor associated with foraging subsistence

doesn't work for other mammal species

Biomechanics has potential to falsify the hypothesis that selection on male contest competition was important in hominin evolution

-as is true for running, the physical demands of fighting are high
-regardless of the species, the reproductive fitness stakes are high when males fight
-if physical aggression was important in the evolution of hominins, it should be reflected in the anatomical characters that distinguish hominins from the other primates

Male contest competition

-mode of sexual selection in which mating opportunities are obtained through using force or threat of force to exclude same-sex competitors

Evidence that human aggression is tied to male contest competition comes from

-phylogenetic comparisons/analyses of primates
-archaeology
-population genetics
-analyses of male/female dimorphism based on sexual selection theory
-evolutionary psychology

Testing the contest competition hypothesis

-there are characters that may improve performance in a particular type of fighting: grappling and striking with the arms
-in hominins, the mode of striking is unique among apes: punching with fists

Three experiments that we have used to test the hypothesis that hominins are anatomically specialized for punching

-hand proportion that allow a clenched fist
-sexual dimorphism in striking power
-beards as armor

The shape of the human hand

-human-like hand proportions that would have allowed a clenched fist posture appear in the fossil record at roughly the same time as habitual bipedalism
-allow us to make and use tools
-more precision and grip

Human sexual dimorphism in behavior

Variance in reproductive success is greater in males because females are picky about who they mate with. This means that males compete for access to mates. In mammals, that competition is usually mainly physical. This leads to the expectation that males will be more willing to take risks, particularly when they are young.

Fatal fighting

occurs in which an individual's lifetime reproductive potential is at stake

Homicide differences between genders

-males were 3.2 times more likely than females to be murdered
-males were 10 times more likely than females to commit murder

Because human males invest in their offspring...

-they may be more concerned about paternity than are males of other species
-relatively intense jealousy may be common

Imbalance of power

humans form a partnership to reproduce, but one partner invests more

xenophobia

anatomy and physiology define the limits of behavior

Goal of structural violence

-discrimination, suppression, and/or exploitation
-males are predisposed to xenophobia because these emotions and beliefs make it easier to marshal the fear and anger needed to attack other groups and to be ready to defend one's community from threats from other groups

What did Hobbes say?

-the evolutionary roots of much of the aggression and violence that plagues modern societies may ultimately lie in the selection that shaped our mating system
-state societies made us safer

What did Keeley say?

-Rate of death in state societies was higher than in non-state societies
-looking at ethnic and archaeological record

What did Pinker say?

-looked at historical record after Keele
-why violence has declined

Overall conclusion from everyone's discoveries?

-we live in one of the safest places in comparison to history
-through time violence is decreasing

Hominin Characters

Astralopithecus afarensis (small body)
-bipedal posture
-adducted big toe
-human-like hands
-big brow ridge
-small canines
-gorilla-like sexual dimorphism
-jaw is more robust

Homo erectus

-same body build as us and same statue as us
-skull was still robust

Homo sapiens

-decrease in robustism of face
-decrease in sexual dimorphism of face
-change the behavior from gorillas just fighting to not only fighting but also cooperation
-this behavior change results in change in biological features

Human face is...

-neotenic: retention of ancestral juvenile features
-pedomorphic

Humans are dynamic species

-we are changing so fast that sometimes our physiology is out of phase with our modern lifestyle

Allometric Scaling often...

required to maintain function

Functions related to surface areas

1. Gas exchange
2. Nutrient Absorption
3. Heat Transfer

Functions related to cross sectional area

1. muscular force
2. strength of structures

Functions related to volumes

1. Mass
2. Mechanical loads
3. Energetic cost
4. Energy storage
5. Metabolic rate

Functions related to length

1. locomotor economy
2. Rotational inertia
3. Speed of muscle shortening

Analysis of Size

-large animals have a low surface to volume ratio
-they can retain heat but can't dissipate heat

Relationship between size and strength

An ant can lift 10 times its own body weight, and it can fall hundreds of meters without injury

Scaling

the study of size and its consequences

isometry

two things increase at equal rates

allometric

two things increase at different rates

Maximum force a muscle can produce

is a function of its cross-sectional area

Some things are lost with race being a social construct perspective

Population differences
-skin, hair, eye color
-metabolic enzymes: lactose, carbohydrate metabolism
-brown fat
-physique
-sexual dimorphism

Implications
-physical performance
-health
-CRT

Critical race theory

cross-disciplinary examination, by social and civil rights scholars and activists, of how laws, social and political movements, and media shape, and are shaped by, social conceptions of race and ethnicity

Personal Fitness

the number of offspring that an individual begets (regardless of who rescues/rears/supports them)

Inclusive fitness

the number of offspring equivalents that an individual rears, rescues, or otherwise supports through its behavior (regardless of who begets them)

Evolution of Altruism

-Hamilton's rule describes mathematically whether or not a gene for altruistic behavior will spread in a population
-c

What does natural selection maximize over time?

fitness

Sexual selection

-natural selection on competition for mates
-depends on there begin two different sexes with distinct gamete properties
-Anisogamy underlies the evolution of sex differences in behavior and morphology

Anisogamy

-females have large nutritious eggs
-males have small, mobile sperm
-underlies the evolution of sex differences in behavior and morphology
- leads to the evolution of one sex competing for access to the other sex and to sex differences in anatomy and behavior
-leads to different strategies to achieve the same goal of reproducing
-evolution of a sex that competes for access to the other sex

Who has greater variance in reproductive success

Males

Dichotomy

which gametes, eggs or sperm, an individual produces

Continuums

-sexual differentiation of the brain and body, as well as gender identity and orientation

Even sex is sometimes fluid

-some invertebrates produce both eggs and sperm, at different points in their lives or at the same time
-there are species of fish in which all individuals start off as female and some eventually become male
-the sex of many reptiles is not determined by their genes, but by the temperature of the place the female lays her eggs

Sexual selection theory

-explains why there are males and females; different mating systems in different species and differences between males and females
-can not explain the spectrum of human sexual identity and orientation

Sexual Differentiation

-explains the spectrum of sexual physique, behavior, identity and orientation
-can not explain the evolution of different mating systems and sexual dimorphism

Sexual differentiation of the brain is a function of hormonal actions at key points in development

-how gender identity and sexual orientation develop
-allows there to be a spectrum rather than a dichotomy
-a spectrum may be a synapomorphy of mammals and it is something that we use to our advantage

A two step scenario for the evolution of sexual dimorphism

1. male competition results in selection for larger males. This sexual selection, acting on body size genes on the X and autosomal chromosomes, makes the species larger. Both males and females get larger as a result of sexual selection on males
2. Sexual dimorphism evolves later as a result of natural selection for optimal body size. Natural selection for survival favors genes that secondarily reduce the size of females

Mating Systems: sexual selection and sexual dimorphism

-Monogamous Swans: low sexual selection
-Polygynous Sage Grouse: Intense sexual selection

Handicap hypothesis

suggests that male sexual characteristics only convey useful information to the females if the traits confer a handicap on male survival
-if the courtship display is somehow deleterious to the male's survival, it becomes a test females can use to assess male quality
-males who excel at courtship displays prove that they are of better quality and genotype, as they have already withstood the costs of having these traits

Examples of the information that the handicaps convey

-avoid predators even though they are more vulnerable to predation
-surviving parasites and pathogens
-acquiring resources needed to support the extravagant traits in spite of locomotor handicap

Responses to Stress

1. Fight Flight Response
2. Tend and Befriend

Fight Flight Response

-more common in men
-emotional and behavioral response to stress that increases the readiness for action

Tend and Befriend

-more common in women
-behavioral reaction to stress that involves activities designed to create social networks that provide protection from stress

2 main examples of sexual dimorphism

1. sexual dimorphism in size
2. sexual dimorphism in weapons

2 ways to compete

1. female choice
3. male contests

Monogamous mating system

little dimorphism, very low aggression

Polygynous matin system

High sexual dimorphism, intense male-male fighting

Physical competition

-body size sexual dimorphism is generally found in polygynous species in which males compete through fighting and the threat of fighting
-the level of size dimorphism is correlated with the level of polygyny
-relative size of male weapons is correlated with dimorphism in body size and with the level of polygyny

Avian skin

-generally thin
-aglandular
-feathers: most complex epidermal structures of vertebrates

Adaptive radiation of feathers

-a feather is a sheet of mature, dead keratinocytes organized into a set of interlocking slits
-they are more complex integumentary structures vertebrates produce
-used for insulation, flight, sensory

Feathers growth and molding

-epidermis invaginates the dermis
-formation of feather is due to interaction between dermis and epidermis

Sinosauropteryx

-earliest feathered dinosaur
-125 mya
-longest known specimen reaches up to 1.07m in length with an estimated mass of 0.55 kg
-hair like bristles

Caudipteryx

-feathered dinosaur
-just a few tiny teeth

Difference between strength and tough

-strength: amount of force it takes to break an object
-tough: amount of energy it takes to break an object
-something that is tougher can stretch more before it breaks

Primitive Cervids

-no antlers
-enlarged canines
-small body size
-as habitat opened, both cervids and bovids increased in size and then came the independent evolution of antlers
-opened habitat leads to this due to ability to travel further, sexual selection, females can be in larger groups which leads to males competing

Other cranial appendages

-rhino horns: epidermal only
-pronghorns: permanent bony core; outer epidermal covering is branched and shed
-giraffe horns: permanent bony core and skin covering

Mammalian skin glands

-3 main classes of glands
-sebaceous gland: hair, secretes oil
-eccrine sweat gland: evaporative cooling
-apocrine sweat gland: releases pheromones
-all located in the dermis

Sebaceous glands

-wax glands
-Meibomian glands

sweat glands

-apocrine
-eccrine

Apocrine sweat glands

-axillary and inguinal regions
-scent glands
-mammary glands

Eccrine sweat glands

-varied distribution and density

proposed evolution of the mammary gland from a mucus secreting gland

-initially wasn't used for nourishment
-used to protect offspring from bacteria
-enzyme in lactation to surround fat and allow it to move through water

Fur vs blubber

-fur increases thickness of insulatory layer
-blubber is hypodermis, if you keep blood away from dermis, blubber is a good insulator

Advantages of sweating

-additional evaporative surface
-independent of ventilation
-independent of pH control
-can talk and regulate at the same time

Advantages of panting

-warmer skin
-little or no salt loss
-forced convection
-fur or feathers don't interfere

Humans are unusual mammals

-no other species sweats as much
-higher level of neuronal control of sweat glands
-hairlessness increases convection

What limits the stamina of cheetahs?

-evaporative cooling through panting is not enough so the body temp rises
-the body temp cannot become too high
-other animals can't dissipate heat like we can by sweating so their body temp continues to rise

Breasts in humans

-we are the only species with breasts
-mammary glands are a form of modified apocrine sweat gland
-all mammals have mammary glands
-only humans have permanent breasts
-it is not the gland that is permanently enlarged structure, but the adipose tissue and suspensory ligaments