ANT 201: Week 5

Speciation + Taxonomy 09/26/23

What defines a species?

The most used definition today ↴

Biological Species Concept: same species if they can interbreed and produce viable, fertile offspring

→ Viable = can survive

→ Reproductive Isolation = some species can produce but their species cannot produce

Some issues with this definition

• Some species are asexual and autonomous (produce on their own)

Other Definitions

Morphological Species concept: species defined by similarities and differences in morphology

Some issues with this definition

• Sexual dimorphism (differences in gender)

NOTE: there are multiple definitions of species but these are the most common two

MODES OF SPECIATION

Allopatric: geographic isolation

• Geographic barriers separate species for so long that they become distinct species

Sympatric: no geographic isolation

• Isolation within a population that over time becomes its own species

REPRODUCTIVE ISOLATION

Prezygotic: prevents fertilization from occurring in the first place

• Geographic isolation
• Incompatible genitalia
• Gametic isolation (egg + sperm can’t combine)
• Behavioral isolation (diff mating rituals)
• Temporal isolation (mating seasons differ)

Postzygotic: barriers to reproduction after zygote forms

• Hybrid inviability

↳ (often due to genetic incompatibility, such as chromosome count)

Ex: humans have 46 chromosomes and chimps have more meaning if they were to mate it wouldn’t survive because the chromosome count is off

• Hybrid sterility (Liger + tigons)

↳ exist but cannot reproduce themselves

TIMING OF SPECIATION

Refers to how quickly microevolution can occur

Traditional Idea

Phyletic Grdaualsim: slow progression to a new species over time

However…

Punctuated Equilibrium: remains the same for a long period of time followed by a sudden and quick speciation event

TAXONOMY

Linnaeus: nested categories based on similarities

Binomial Nomenclature: double named [combination of genus and species]

• Genus = capitalized
• Species = lower case
• Both are italicized

Note: if handwritten you underline it

Ex: Homo sapiens → can be abbreviated to H. sapiens in papers

CLADOGRAMS

Clade: group of species sharing evolutionary relationships

• Includes closely related species (at ends of branches) and their last common ancestor (LCA-cat nodes)

→ nodes are the ones that connect the species

Ancestral Trait: trait remains the same in ancestors and descendants → hasn’t been modified

• Shared with other species

Ex: having 4 limbs (both humans and dogs have 4 limbs)

Derived Trait: traits which have changed from the ancestral state; evolutionary novelty

• defines/unique to a clade

Ex: humans walking on two feet

BEWARE of Convergent evolution: several species that aren’t closely related evolved with similar traits

Ex: bats and birds both have wings

Parisomy: simplest scientific explanation

→ if you have to mark it more than once on a cladogram it’s likely not parsimonious unless its in the case of convergent evolution

Primate Clade 09/28/23

Why study primates?

Knowing what traits we share with other primates helps us define what IS human

• Studying primate relationships in particular we could look at behavior and anatomy which will help us when analyzing human fossils

What makes a “primate”

+ Some ancestral traits for primates (inherited from mammalian ancestors)

• Body hair
• Maintain body temp
• Mammary glands [ability to produce milk]
• Give birth to live young
• Larger brain
• Pentadactyl (ancestral to mammals) [5 digits]

NOTE: Ancestral mammalian dental formula= 3.1.4.3

Human: 2. 1. 2 .3 → [we’ve lost some]

• Primates defined by a suit of derived traits
• Adaptation for arboreal life [living in trees]
• Humans live on land because we derived the traits in order to do so

Types of primate locomotion:

• Quadrupedalism [walking on 4 limbs]
• Either terrestrial and/or arboreal
• Vertical clinging and leaping
• Brachiation (only apes) [climbing monkey bars movement]
• Bipedal [(only humans)

Highly Developed Vision

• Less reliance on smell + more emphasis on vision
• The area of smell in our brain has been reduced

[we have short snouts]

• Forward-facing eyes (convergent)
• Stereoscopic vision (depth) [field of vision in both eyes overlaps]
• Primates will have a post-orbital bar [open] or a post-orbital plate [closed for protection]

Hands and Feet

• Prehensile [grasping] hands with opposable thumbs/big toes
• Ability to touch our thumbs with our other finger
• Other primates can do the same with their toes
• Our fingers have nails
• Sensitive fingertips [tactile pads]
• Dermal ridges [fingerprints]

- Dogs have this on their noses

Other Features

• Larger brains for body size, more complex brains
• Extended life History
• Show growth
• Longer life [slow development]
• Infrequent reproduction, few offspring per pregnancy
• Higher parental investment
• Sociality
• Grooming
• No migration

Strephsirrhiness

• Retain more ancestral traits
• Higher reliance on smell compared to other primates
• Rhinarium [wet nose, like on dogs]
• Scent marking
• Eyes less convergent than other primates
• Longer snout than other primates

“Other primates”= Haplerrhines

• Small body size
• Tapetum Lucidum [the reflection in animal eyes]

Derived Traits

• Grooming claw(s) - 2nd digit
• Tooth comb (or dental comb)

- [certain teeth climbed together] on the mandible

- Made of incisors and canine teeth

• Post-orbital bar

Lemurs

• Only found in Madagascar
• Diverse [
  • Durnal, nocturnal, cathemeral: irregular, either/or
  • Diet varies between species
• Little-to-no -sexual dimorphism [gender difference]
• Females are dominant
• Quadrapedalsim + vertical clinging and leaping (VCL)

Aye-Aye

• Nocturnal
• Rodent-like teeth [never stop growing]
• Ball-and-socket joint for elongated middle finger
• Percussive foraging [listen for grubs and use the long finger to dig them out to eat]
• Pseudothumb -6th digit [for grasping]
• Dental formula: 1.0.1.3/1.0.0.3

- no canines

Lorises, Pottos, and galagos

• Southeast Asia (lorises), Central Africa (pottos + galagos)
• Galagos= ‘bushbabies’
• Nocturnal
• Slow quadrupeds (lorises)

Happlorrhines

[Tarsiers] + [

• Greater emphasis on vision
• No rhinarium
• Smaller snout
• Eyes more convergent
• Post-orbital plate
• Larger brain relative to body size
• No tapetumlucidum
• Most diurnal

Tarsiers

• Southwest Asia
• A mix of traits- difficult to classify
• Strepsirrhine-like
• VCL- long traits
• Small-bodied
• Nocturnal
• Grooming claws (two)

*ex: of convergent evolution b/c it developed separately

• Anthropoid -like

- No rhinarium

- No tapetum lucidum

- Convergent eyes

- Almost full-orbital plate [partial]

Unique traits:

Platyrrhines (New World Monkeys)

• Only non-human primates in Central and South America
• Flat, wide noses-round, outward-facing nostrils
• 3 premolars → usually 2.1.3.3
• Highly arboreal
• Some with prehensile tails [grasping tails]--> with tactile pads

Semi-brachiation → use their tail alongside swinging hands

*Any monkey that has a tail that can grasp is a platyrrhine

Spider Monkeys

• No thumbs
• Prehensile tail

Marmosets and Tamarins

• Smallest monkeys
• Regularly birth twins (normal)
• Many polyandrous with alloparenting

- one female mates with several males

• Derived dental formula → 2.1.3.2

Catarrhines (Old + New World monkeys and Humans)

• Narrow, teardrop-shaped, downward-facing nostrils
• See more colors
• More sexual dimorphism [distinct diffs in gender]
• 2 premolars → 2.1.2.3
• More terrestrial
• Larger body size

Cattarrhines

Cercopithecoids Hominoids

Cercopithecines Colobines

Cercopithecoids (OWM)

• Most-widespread non-human primates
• Bilophodant molars: 4 cusps, line up two in a row on teeth
• Ischial Callosites: sitting pads → red butt

Colobines (Leaf Mokeys)

• Mostly in Asia
• Folivores: diet of leaves

↳ Sacculated stomachs → multi-champer stomach to digest leaves

• Infants tend to have natural coats: different color than adults

Proboscis Monkey [huge nose monkeys]

• Only found in Borneo
• Like to live close to water
• Sexually dimorphic [down to nose size]
• Several webbed toes

Cercopithecines (cheek pouch monkeys)

• Mostly in Africa
• Frugivorous or omnivores
• Presence of cheek pouches

Japanese Macaques

• Northernmost non-human primate
• Grow heavier coats in the winter
• Excellent swimmers
• “Hot tubbing”

Hominoids (Apes + humans)

• Hylobatids: Lesser apes Homindis: Great apes and Humans
• Y-5 molars (more ancestral form present in fossil catarrhines)
• Brachaitors
• Longer arms than legs [no longer true for humans]
• No tails
• Shorter olecranon process
• Longer clavicle
• Wide rib cage laterally
• Extended life histories
• Less offspring reproduction → Long-term parenting

Hylobatids

• Gibbons and Siamangs “lesser apes”
• Southeast Asia
• Gibbons → Frugivorous; siamangs-folivorous
• “Ischail Callosistes”
• Siamamgs have throat sacs for louder vocalizations
• Live in pairs → little sexual dimorphism

Orangutans

• Borneo and Sumatra (Southeast Asia)
• Frugivorous
• Diurnal + solitary → unique to primates
• High sexual dimorphism
• Male bimatrusim→ flanged vs. unflanged

↳ Dom male develops fangs + throat sacs

- only one to mate w/ females

- other males sneak around

• Alternate
• Reproductive
• Strategies

Gorilla

• Found in Africa
• Highly sexually dimorphic
• Knuckle-walking
• Silverbacks
• Folivorous and frugivous
• Largest primate

Chimpanzees + Bonobos

• Found in Africa
• Frugivory

• Some sexual dimorphism
• Knuckle-walking

Bonobos Sexuality

• Face-to-face copulation
• Mothers help sons find sexual partners
• Non-reproductive copulation
• Same-sex sexual encounters
• Oral and manual sexual touching or genito-genital rubbing
• Diffuse tension, pleasure

Humans

• Similariyie with apes
• No tail
• Body adapted for brachiation (except limb length)
• Y-5 molars
• Extended life history
• Similarities with African apes
• Share 96% of DNA w/ gorillas, 98% with Pan [chimps + bonos]
• Knuckle-walking in ancestry [LCA]

Select Human traits

• Vertical forehead
• Mental eminence
• Bipedalism

- Foramen magnum inferior

- Convergent big toe