Lecture notes Evolutionary Developmental Biology (2021)

Evolutionary developmental biology

Lecture 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. 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 (Straalen & Roelofs 1)
Homo sapiens (knowledgeable man):

- Kingdom: animalia
- Phylum: chordata
- Subphylum: vertebrata
- Class: mammalia
- Order: primates
- 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

The African rain forest gave to savannah (10 Mya)  a new ecological niche:
Terrestrial instead of arboreal lifestyle demanded adaptation  all old fossil hominins are found in
(East) Africa

Species to remember:

- Australopithecus afarensis
- Lived in Africa, ~3.5 Mya
- Ancestor of all Homo species
- Mosaic of ancestral and derived traits
- 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

Morphological characteristics of
hominin skulls:

- Brain volume
- Prognathism
- Flaring zygomatic arch
- Sagittal crest
- Supraorbital torus

What is a species:

1. Group of organisms that can produce fertile offspring
- Hybridizations between closely related species possible
2. DNA sequence similarity
3. Behaviour
4. Ecological niche
5. Morphology
- Completeness and number of specimens found important
- Variation within species versus variation between species

, Australopithecus:

- Not all humanlike traits evolved at the same time
- Apomorphic (derived) vs. plesiomorphic (ancestral)
- Skull shape and brain volume largely plesiomorphic
- The dental arcade changed from U-shaped to parabolic and became shorter
- Reduction in canine teeth size in australopithecines, but still significant sexual dimorphism
- Strong dimorphism in body size  gradually disappeared6 species (4.2-2.5 Mya)
- Gradual evolution of various humanlike traits in subsequent species
- Two lineages 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)
 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

Evolution of the brain of genus Homo habilis:

 Use and manufacturing of stone tools:
- Understand fracture mechanics of available stones
- Sensorimotor control over force and accuracy to strike off flakes
- Spatial understanding of where to strike
 Homo rudolfensis  an alternative “first” Homo species
- First appeared 2 Mya
- More humanlike features of the head
- Debated if it is a separate species or part of Homo habilis
- Few fossils remains found
 Species concept problematic in genus Homo

Homo erectus (2 Mya – 108.000 Ya):

- All traits related to bipedalism well developed
- Efficient long-distance runners
- Evolution of less body hair and dark skin colour
- Brain volume (600-1000 cc)  still apelike skull features
- Evolution of larger brains started ~800.000 Ya
- First species associated with hunting large animals; more sophisticated stone tool making
- First human species to migrate out of Africa
- Morphologically very diverse

Modes of speciation:
Reproductive isolation  followed by local adaptation or genetic drift over time.

1. Sympatric speciation  side-by-side evolution
2. Allopatric speciation  a group separates and occupies a
new area
3. Parapatric speciation  origin of a new species on the
border of the distribution range due to local adaptation