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Summary part 1 Evolutionary Developmental Biology
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Summary Part 1 Evolutionary Developmental BiologyLecture 1 – Evolutionary developmental biology introduction
Evolutionary biology:
• To interpret and understand organismal adaptation to environmental conditions
• To explain the diversity of life: the variety of organisms, their characteristics, and
their changes over time
Charles Darwin (1859) → the origin of species:
Evolution is change in the heritable characteristics of biological populations over successive
generations.
Natural selection:
1. Variation in reproductive success
2. Variation in the trait of interest
3. Correlation between the trait and reproductive success
4. The trait is heritable
→ Survival of the fittest
Typological thinking → the “normal” or average condition is the most important aspect to
consider
Population thinking → understanding the variation in a population
Heritable traits with standing genetic variation and possibly subject to selection in humans:
- Behaviour
- Physiology
- Morphology
- Life-cycle traits
Not adaptive:
• Trade-offs, random processes, mismatches, evolutionary constraints
• Claims of adaptation need examination, which can be difficult in humans
Determining if something is adaptive:
1. Observing natural selection experimental evolution in microorganisms,
nematodes, or insects
2. Perturbing the trait move a trait away from its optimum
3. A trait is produced only when it serves a function
→Most of these tests are not possible in humans → model organisms
Tree thinking:
Understanding the position of a species or a trait in a phylogenetic tree → expresses the
relationship among organisms and their evolutionary history.
,Lecture 2 – Story of our ancestors
arboreal mammal (Plesiadapis) is a tree-climbing animal and ancestor
Homo sapiens (knowledgeable man):
- Kingdom: animalia
- Phylum: chordata
- Subphylum: vertebrata
- Class: mammalia
- Order: primates → larger, more elaborated brains; complex social behavior; use tools
- Family: hominidae →no tail; remarkably long periods of nursing and adolescence;
sexual dimorphism
- Subfamily: homininae →bipedalism; brain size; family structure; and sexuality
- Genus: homo
→Anagenesis: gradual evolution of a species
→Cladogenesis: many splits and dead ends
The precise phylogeny is still debated
Hominina: our closest relatives
Species to remember:
• - Australopithecus afarensis
- Lived in Africa, ~3.5 Mya
- Ancestor of all Homo species
• - Homo erectus
- Lived in Africa and Asia, ~1.5 Mya
- African H. erectus ancestor of H. sapiens
• - Homo neanderthalensis
- Lived in Europe and Asia, 600 Kya – 30 Kya
- Similarities to H. sapiens; extinct sister clade
The African rain forest gave way to the savannah (10 Mya). A novel ecological niche:
Terrestrial instead of arboreal lifestyle demanded adaptation. All old fossil hominins are
found in (East) Africa, the great rift valley.
From early hominins to Australopithecus
--The road towards bipedalism--
Ardipithecus ramidus (“Ardi”) (5.8-5.2 Mya)
- Bipedal, but still with primitive traits:
→Most notably, foot with large hallux abduction
Evolutionary adaptation mostly evolves slow.
The species Australopithecus had bipedalism (walking upright on two
feed) accomplished. There is a stepwise reorganization of the entire
skeleton. The basis for the evolution of other “human” adaptations.
,Mosaic evolution: not all trades evolved at the same time, some remained primate.
Apomorphic (derived) vs. plesiomorphic (ancestral)
Australopithecus:
→Lucy:
Australopithecus afarensis (3.2 Mya) excavated in 1974 in Ethiopia.
• - Most complete Australopithecus fossil at that time
• - First to display characteristics of bipedalism and a small brain
• - Settled “brain first” versus “bipedalism first” debate
Mosaic evolution of Australopithecus
- Skull shape and brain volume
are largely plesiomorphic
- Dental arcade: from U-shaped to
parabolic, and smaller
Reduction in canine teeth size,
but still significant sexual
(differences in male and female)
dimorphism in Australopithecus
6 species, 4.2-2.5 Mya
The gradual evolution of various
humanlike traits in subsequent species.
Two genera diverged from Australopithecus
• Paranthropus (2.5-1.4 Mya), characterized by robust and muscular bodies with
apelike features of the head→ evolutionary dead end
• Homo (2.8 Mya - now) →Homo habilis (2.8-1.4 Mya)
Genus Homo
- Use and manufacturing of stone tools
- The evolution of brain volume takes off!
The ecological context of Homo evolution: Start of a period of climatic instability
, Homo habilis (“handy man”): the first
Homo?
- Keith (1948): brain volume >750
cc
- Leakey (1964): Use of tools
defining, brain volume >600 cc
• Primitive stone toolmaking in
Australopithecus (2015)
- Wood & Collard (1999): Cladistic
analysis places Homo habilis
outside genus Homo
Homo erectus, 2.0 Mya – 108’000 ya
Clearly more humanlike features
• Efficient long-distance runners
• Evolution of less body hair and dark skin color
• Brain volume 600-1000 cc, but apelike skull features
• Evolution of larger brains started ~800’000 ya
• Hunting large animals; possibly habitual fire use; sophisticated stone tool making
H. erectus first human species to migrate out of Africa. Its morphology is therefore diverse:
• H. ergaster, Java Man, Peking Man, H. georgicus, H. antecessor, H. naledi
What is a species?
1. Group of organisms that can produce fertile offspring
• Cannot be examined in fossils....
• Hybridizations between closely related species possible
2. DNA sequence similarity
• Also problematic for old fossils
3. Behavior
4. Ecological niche
5. Morphology
• Completeness and number of specimens found important
• Variation within species versus variation between species
Morphological characteristics of hominin skulls
1. Brain volume,
2. Prognathism,
3. Flaring zygomatic arch,
4. Sagittal crest,
5. Supraorbital torus
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