Humans in the Natural World. Humans are vertebrates with, among other features: 1. an internal, segmented vertebral column 2. an internal, segmented skeleton. 3. bilateral symmetry. Humans are also mammals , with: 1. maintenance of constant body temperature. 2. birth of live young.
1. an internal, segmented vertebral column
2. an internal, segmented skeleton.
3. bilateral symmetry.
1. maintenance of constant body temperature.
2. birth of live young.
3. mammary glands to nurture the young over a prolonged period of growth and development.
4. large brain associated with ‘intelligence’
5. A dentition made up of several different kinds of
teeth (incisors, canines, premolars and molars)
that function together to allow the animal to chew.
1. Basic adaptations to life in the trees (arboreal way of life).
2. The retention of the five digit hand and foot.
3. Development of acute vision with depth perception.
4. Relative lack of an acute sense of smell.
1. Social Living
2. Daytime activity cycles (diurnal)
3. diverse dietary patterns.
(It should be emphasized, again, however, that there is no fossil evidence documenting the evolutionary history of either of these two primates.)
If the earliest of the genetically derived dates is correct (8 myr), then we have fossils documenting only the last half of human evolution.
If the later date is correct (5 myr), then it would now appear that we have the earliest fossils of the hominid line, and these irtually the entire human fossil record and the earliest fossils should be expected to document our initial beginnings.
humans chimpanzees gorillas
5 - 8 myr
common ancestry of humans and
An evolutionary diagram of human and African ape
relationships, based on various genetic studies
As Profs Liberman and Urban have already noted, modern humans are unique in having:
1. Complex culture with a wide variety of societal norms in behavior.
2. Language and symbolism.
very large brains in comparison to
our body size.
small, non-projecting faces.
The major question here is: when did these distinctive features of modern humans appear in the course of our evolution?
Apes possess large, projecting canine teeth, while hominids have reduced canines.
The examination of the gross anatomical features of humans and apes reveals their close similarity.
Comparisons of the genetic materials of the African apes and humans documents that these creatures are more closely related to each other than to any other living animal.
millions of years ago
If you did not know about the fossil evidence, how many of you would have expected our early ancestors to be distinguished first and foremost by increased head size?
This is, after all, the seat of our intelligence and ‘humanness’.
Although there are at least six recognized species, all australopithecines possessed in common the following:
1. the anatomy of bipedalism.
2. small, non-projecting canines.
3. incisors not much bigger than in humans.
4. back chewing teeth, the premolars andmolars that were huge.
5. very large jaws and jaw muscles.
6. australopithecines had small brains:
volumes range from 400-500ml.
modern humans: 1400m.
(1000 ml = 1 liter, 1 US quart = 946 ml.)
Sexual dimorphism in modern humans?
What do you think?
Is there a set of differences that might distinguish males and females?
If sexual dimorphism is no longer present in modern humans, what do you think are some of the reasons it disappeared during the course of human evolution?
1. The australopithecines can be placed within a time ordered evolutionary lineage, with the earliest evolving into later forms, and ultimately, into early members of the genus Homo, who will eventually evolve into modern humans.
millions of years ago origin of hominids
2. Early in australopithecine evolution, they spread into different environments, and underwent divergence, evolving into a number of different species, each with somewhat different biological features, yet all possessing the ancestral traits. In time, only one species evolved into Homo.
millions of years ago origin of hominids
2. large back teeth, and big chewing muscles.
3. brains sizes similar to those of the apes.
4. some (all?) were sexually dimorphic.
5. It is unclear if they made tools. Most have not been found with tools.
1. Taphonomic investigations are only partially able to reconstruct the habitats of the various species, and questions remain about their ability to utilize a mosaic of environments, as do chimpanzees.
2. The anthropologist Jane Lancaster has observed that “the australopithecines are all extinct, and so are their behaviors”. How much like living animals and human gatherer/hunters these creatures were remains an open question.
It is unclear whether the various australopithecine species occupied different environments, or whether, like chimpanzees, they were capable to utilizing a variety of seasonally related habitats, including forests, woodlands and open grasslands.
It also uncertain just how widely distributed these creatures were. Did they live throughout Africa?
Outside of Africa?
Little specific information is available about what these creatures ate, and the possible differences in diet between the various kinds of australopithecines.
It is often assumed that those australopithecines with the huge molar teeth, the so-called ‘robust’ australopithecines, were eating a diet of coarse, gritty vegetable foods.
However, the smaller ones, like ‘Lucy’, known as ‘graciles’ also possessed very large teeth for their body size, and both kinds of australopiths had thick enamel on their teeth, and also had very heavy dental wear.
Investigations of australopithecine behavior have focused on:
1. Were they bipedal chimps or humans in fur suits.
2. Brain size and brain and body size estimates.
3. Patterns of maturation.
4. Dietary reconstructions.
5. Social organization.
6. Tool use.