ANT Lecture 1

Important trends in evolution

1. bipedal (upright) walking

2. increasing brain size

3. changes in dentition

What ways to scientists learn about human evolution

1. fossil record

2. archeology

3. molecular evidence

the two types of dating methods

1. relative dating

2. direct dating

relative dating

1. orders past events relative to one another

   1. Lower precision

   2. Uses geological principles of stratigraphy (eg, biostratigraphy)

Biostratigraphy:

Correlates the relative ages of strata (layers) using the fossils in them

1. Ex: Hipparion: 

   1. Came into africa from eurasia, dated between 10.5 - 12 Ma

   2. If you find Hipparion in Africa, the stratum probably dates between 12 Ma and 10.5 Ma

   3. But

1. This requires prior knowledge of the time range of the species

direct dating

1. returns numeric dates (years, etc)

   1. High precision (with error)

   2. Uses chemical properties of stone and biological materials

radioactive methods

1. Measures the decay of unstable radioactive isotopes in sediments/remains

2. Based on principle that radioactive isotopes change into stable isotopes at a steady rate

3. Info needed

   1. Event that starts the decay “clock”

   2. Known rate of decay

evolution is not..

…progressive

…has no end goal

fitness

depends on the environment- there is no objective “Better” species

bipedalism

walking and running upright on two legs

Facultative bipedalism

1. used with other locomotion as needed

habitual bipedalism

1. used day-to-day as a main form of locomotion

obligate bipedlaism

used exclusively; highly efficient

What Parts of the body are most important for understanding bipedalism?:

1. bicondylar angle

2. arches

3. lumbar spine

1. Bicondylar angle:

the oblique found in the human femur which centers body weight over the feet

arches

are a part of human feet to absorb shock

Hypothesises for increasing brain size

1. ecological brain hypothesis

2. social brain hypothesis

ecological brain size

1.  primates evolved large brains to find food, like fruits, in difficult environments

social brain hypothesis

1. primates evolved large brains to manage living in groups with complex social relationships

2. All primates have a high EQ (Encephalization: Quotient: ratio of brain mass to body mass) relative to to other mammals

3. This trend is even more pronounced in hominins

4. Brain size increased dramatically in hominins during the Pleistocene (2.6 Ma)

dental changes

1. Humans have relatively smaller teeth than other primates- especially canines

“Honing complex” between canine and P3 (premolar) absent in humans

possible explanation for dental changes

1. Lack of male-male competition 

2. Use of tools

2. Chimp detention: large canines and C-P3 honing complex 

the fossil record

1. Fossils of extinct organisms

2. Geological context

3. Environmental reconstruction

What are fossils?:

1. Evidence of plant and animal life preserved in the Earth’s crust

2. Mineralized organic material

Making sense of fossils: comparative morphology

1. We gain useful information from fossils thru comparison 

2. Comparison among fossils and with living species

3. ancestral and derived traits

ancestral trait

1.  inherited unchanged from an ancestor

   1. Ex: 5 fingers on each hand (pentadactyl) in ancestral for humans because we inherited the trait from our common ancestor with other animals

derived

1.  new trait in a species or group, relative  to its ancestors

   1. Ex: the bony chin is derived in modern humans because our common ancestor with our closest relatives did NOT have this trait

1. Symplesiomorphy:

shared-ancestral

1. Synapomorphy:

shared-derived

1. Autapomorphy:

unique derived

1. Homoplasy:

independently shared (not inherited from a common ancestor)

1. Ex: wings are a classic homoplasy they have evolved separately several times in different lineages

Fossilization steps

1. Decay of soft tissue 

2. Rapid burial by sediment

3. Organic material slowly replaced by minerals

4. Exposure by erosure

5. is very rare: the vast majority of plants and animals never become fossils

6. Different factors influence if a particular organism’s remains are preserved or destroyed 

Law of Superposition:

1. layers of sedimentary rock are older than the layers above and younger than layers below

Law of original horizontality: 

1. Layers of sediment are deposited horizontally under gravity

2. Sedimentary rocks left undisturbed will remain horizontal

3. Layers have been tilted or deformed did so after formation

Law of crossing-cutting relationships

1.  If a fault or other body of rock cuts through another body of rock, then it must be younger in age than the rock through which it cuts and deposits.

1. Law of Faunal Succession:

1. sedimentary rock strata contain fossilized flora and fauna

2. These fossils succeed each other in a specific, reliable order that can be identified over wide distances

3. Makes it possible to use biostratigraphy to date fossils

1. Archeology:

1. The study of material culture

2. Using artifacts (objects made/used by people) to understand the past

3. Our key to understanding behavior in the past

4. Dynamics (what happened in the past) → Statics (artifacts)

1. The hominin archaeological record:

1. 3.3 Ma to present

2. Composed mainly of stone artifacts until 200 Ka

Molecular evidence:

1. Newest line of evidence for researchers

2. Modern human DNA

   1. Divergence from other living species (“molecular clock”)

   2. Natural selection for specific traits

   3. Introgression between populations

3. Ancient DNA and proteomics 

   1. Biological material preserved in ancient remains

1. The Molecular Clock:

1. Estimates the time of split between lineages

2. Difference in immune systems (ID) between two species is related to the amount of time since they diverged 

3. Assumes a constant rate of change in immune system

1. Issues with the molecular clock:

1. Relies on the fossil record for estimation of the mutation rate

2. Assumes a constant rate of change in ID (or other mutations/differences)

3. Large standard deviation

4. Does not match fossil record:

   1. Short chronology does not fit with the oldest hominin fossils eg, Sahelanthropus and Orrorin