Samenvatting
Samenvatting Evolutionary Developmental Biology
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Lecture 2 Story of our ancestorsPrimates have larger, more elaborate brains compared to other animals. They also have a complex social
behavior and make use of tools. When looking specifically to hominidae-species, there can be seen that
they al have no tail, have a long nursing period and adolescence and have sexual dimorphism.
The Australopithecus afarensis lived in Africa, about 3,5 million years ago. It is the ancestor of all the
Homo species. The Homo erectus lived in Africa and Asia, about 1,5 million years ago. The African H.
erectus is considered to be the ancestor of the H. sapiens. The Homo neanderthalensis lived in Europe
and Asia, about 600.000-30.000 years ago. It has similarities to H. sapiens and it is considered an extinct
sister clade.
About 10 million years ago, the African rain
forest gave way to savannah. The terrestrial
instead of arboreal lifestyle demanded
adaptation. The first thing that involved in the
Australopithecus species is bipedalism. The
Ardipithecus ramidus (5,8-5,2 Mya) was
bipedal, but still with primitive traits. Most
notably were his feet with large hallux
abduction. Bipedalism kept evolving and by
the time the Australopithecus was reached,
bipedalism was accomplished. Bipedalism was
the basis for evolution of other ‘human’
adaptations. Mosaic evolution is the occurrence, within a given population of organisms, of different
rates of evolutionary change in various body structures and functions.
Lucy was found in 1974 in Ethiopia. She was the most complete Australopithecus (afarensis) fossil at
that time and the first one to display characteristics of bipedalism and a small brain.
Not all humanlike traits evolved at the same time. There are two different types of traits:
1. Apomorphic traits derived (evolutionary novelty)
2. Plesiomorphic traits ancestral
Trait Chimpanzee Australopithecus a. H. sapiens
Locomotion Quadrupedal Bipedal Bipedal
Brain volume 275-500 cc 380-530 cc 1240-1440 cc
Skeleton Apelike Mixed Humanlike
Shape of skull Apelike Mostly apelike Humanlike
Teeth Large canines; Small canines; Small canines; no
diastema diastema diastema
Sexual dimorphism Yes Yes Little
The first Homo species is called the Homo habilis (handy man). It was defined by its usage of tools and a
brain volume of more than 600 cc. The Homo erectus has more humanlike features. They were efficient
long-distance runners. The evolution of less body hair and a darker skin color has been found. The brain
volume of the Homo erectus got a lot bigger, from 600 up to 1.000 cc, but they still had apelike skull
features. They hunted large animals, possibly used fire and more sophisticated stone tools making,
compared to Homo habilis. The Homo erectus was the first Homo species to migrate out of Africa. This is
why the found fossils were morphological diverse.
The definition of a species is that it is a group of organisms that can produce fertile offspring. However,
this can not be examine in fossils and hybridization between closely related species is possible. Species
, also have DNA sequence similarity, which is also problematic for old fossils. To determine if two
organisms belong to the same species, there can be looked at the behavior and the ecological niches.
Also, morphology used to determine this. In that case, the completeness and number of specimens
found is important.
Speciation requires reproductive isolation, so they are not able to produce offspring together and the
adapted traits will only be seen in one specie. There are different types of speciation:
1. Sympatric speciation side-by-side evolution (rare) can happen due to differences in lifestyle
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
Sympatric speciation Allopatric speciation Parapatric speciation
Lecture 3 Migrations & hybridization
The archaic humans are the species that look the most similar to the humans today. These are the Homo
neaderthalensis, the Homo denisovae and the Homo floresiensis. There are two theories for the origin
of the Homo species:
1. “Out of Africa” the Homo sapiens originated once, in
Africa, and replaced all the other Homo species. This
means that all humans descend from an African ancestor.
2. Multiregional evolution the Homo sapiens evolved at
several places from local, older hominins. Asians descend
from an Asian H. erectus and the Europeans from a
European H. erectus. The genetic differences between
Africans, Europeans and Asians derives from the dispersal
of the Homo erectus.
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