evolutionary trees

[karam]

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wh yare there alternate evolutionary trees when they are all based on the same fossil evidence?

what characteristics distinguish the primates from other placental (eutherian) mammals?

[Irskin]

Due to the arbitary nature of classification, lack of fossil evidence and different interpretations of the same evidence, there are many alternative models for human evolution. For example, the linear relationship between the hominins where one species evolved directly into another is based on anotomical information alone (the structure of the fossils). Recent technological advances has meant that the fossils can now be compared on a molecular level. Their mitochondrial DNA (mtDNA) can be compared and evolutionary relationships are now more commonly based on this biomolecular evidence. Now the models for human evolution are more branched shaped (phlogentic trees or cladograms) because some species are believed to be more closely linked than others genetically. For example, Homo sapiens and Homo neanderthalensis both evolved from the one common ancestor, Homo heidelbergensis instead of evolving in the order: heidelbergensis, neanderthalensis and sapiens.

Also, the two main feature that distinguish primates from other mammals are that 1. they have grasping fingers and toes (opposable thumb)
2. Eyes that are positioned at the front of the head producing overlapping vision (binocular vision)

Only primates have both binocular vision and grasping hands

I hope that helped.

[Kyroth***]

Because that same fossil evidence can be interpreted multiple ways.

Think of CSI or something. Two detectives find the same piece of evidence. One says it is proof that the best friend was the murderer. The other beleives it is proof that the person is not dead at all. Two very conflicting points of view, both drawn logically from the same piece of evidence. It's the same with the fossil record.

Not everyone believes everyone elses theories. Some place emphasis on eye ridges. Others believe cranial capacity is more important. The fact is we don't know what happened, and we can only guess. And being what we are, we don't always agree with each other.


This is my answer to the primate dot point.

Hand/foot: In most primates, hand and foot are recognisably different from each other. Feet are used for locomotion, hands for grasping, though this can be interchangeable. All primates have an opposable thumb/toe, most primates have one on every limb. All primates have five digits and mostly nails rather than claws.
Skull shape: Primates have larger brains and thus skulls than other creatures. The skull is rounded at the back, with a flatter face, reflecting the importance of the eyes as a sensory organ and the lesser importance of the nose.
Brain size: Primates have a very large brain in comparison to their body size.
Vertebral column: The arrangement of the vertebral column in primates makes an upright stance possible. Those with the highest degree of upright stance (humans) have as S curvature, this decreases as the degree of uprightness lessens.
Vision: Primates have forward facing eyes, allowing them to focus on the same thing, creating stereoscopic vision. This assists in depth perception, important for swinging from tree to tree. They have colour vision, unlike most mammals, reflecting their activity during the day.
Reproduction: Primates usually give birth to one live young at a time, after a comparatively long gestation period. This reflects the higher development of the brain.
Group bonding: There is a comparatively long period of parental care in primates, and the young remain with the mother for a long time. Primates live within groups with complex social structures. Often the group is subdivided into family or age groups, with each individual understanding their position within the group.