Evolution
Evolution
4th Edition
ISBN: 9781605356051
Author: Douglas Futuyma, Mark Kirkpatrick
Publisher: SINAUER
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Chapter 21, Problem 1PDT
Summary Introduction

To determine: The evidence that shows that the most recent common ancestor of chimpanzees and humans was much more arboreal than modern humans.

Introduction: Humans are believed to have evolved from the last universal common ancestor of all the living organisms. Chimpanzees and humans share a common ancestor from where hominins diverge to give rise to modern humans.

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Explanation of Solution

According to the fossil records, Chimpanzees and humans have evolved from the same common ancestor. Humans have evolved from apes and the most common relative of humans are chimpanzees. About 7 million years ago (mya), hominins diverged from chimpanzees to evolve into modern day humans. The members of the hominin clade include Sahelanthropus, Orrorin, and Ardipithecus. A 4.4 million year-old fossil deposit of Ardipithecus ramidus in Ethiopia suggested that they had many apelike features including opposable big toe which are adaptations for climbing.

About 3.5 Mya, the fossil of Australopithecus afarensis shows ancestral features common to the ancestors of humans and chimpanzees. These features include, lower face, long arms relative to the legs, and the limb structure shows that these species climb trees along with walking.

The first fossilized footprints have been found about 3.5 Mya in Tanzania. So, it can be assumed that before this, the common chimpanzees- human ancestor lived more arboreal life.

One of the early species of Homo was Homo habilis which resembled modern human had limbs which suggested that they had an ability to climb.

Summary Introduction

To explain: The change in the conditions of Africa, which selected for a less arboreal lifestyle.

Introduction: Humans are believed to have evolved from the last universal common ancestor of all the living organisms. Chimpanzees and humans share a common ancestor from where hominins diverge to give rise to modern humans.

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Explanation of Solution

The change in the climatic conditions leads to various drastic changes in the lifestyle of species. The earlier human ancestors were adapted to live an arboreal life because of the wet climate of Africa. The change in temperature and precipitation has caused the land to become dry. The hominins now started living on land instead of trees. This change favored walking instead of climbing.

The other theory which supports this is that the competition in arboreal life increased. This caused some of the species to leave trees and start living on land. Earlier evidence showed that the member of hominins such as Australopithecus afarensis was adapted to climb trees as well as walking. Now, natural selection comes into play and selects walking over climbing which is then passed on to next generation.

This can be explained on the basis of “survival of the fittest”, as the competition increased, the more fitted organ is favored and is selected by natural selection. In this case, walking was preferred over climbing as the climatic conditions of Africa were more suited for walking. This also helped the species to pluck fruits and also running away from prey. The drier environment also leads to loss of body hair to keep the body temperature low.

Summary Introduction

To explain: The cause of changes that did not evolve in chimpanzee’s lineage.

Introduction: Humans are believed to have evolved from the last universal common ancestor of all the living organisms. Chimpanzees and humans share a common ancestor from where hominins diverge to give rise to modern humans.

Expert Solution
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Explanation of Solution

Humans and chimpanzees are believed to have evolved from a common ancestor. They two belong in the same group called apes. After several evolutions, human ancestor diverged from chimpanzees to evolve into modern day human. Human and chimpanzees are related cousins; humans did not evolve from chimpanzees. This fact is the main reason for the evolution of human becoming less arboreal.

Evolution occurs differently in different species, some changes that were adapted by the diverged group of hominins were not adapted by chimpanzees and thus they did not develop the same characters as humans.

Hence, humans and chimpanzees share a common ancestor which was more arboreal as compared to the modern day human.

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Ardi (Ardipithecus ramidus) lived 4.4 million years ago, close to the time that our lineage diverged from chimpanzees suggesting that Ardi might be more similar to the last common ancestor than extant chimpanzees or humans. Ardi has small teeth like ours, indicative of a generalized diet. So small teeth are older than larger teeth of extant chimpanzees! Ardi also had limbs shaped more like ours than chimpanzees’. Ardi’s skull also shares other features with ours – for example, it is relatively narrow. The hypothesis we tested assumed that the hominin ancestor resembled chimpanzees, and the assumption was quite common among paleoanthropologists until recently (Lovejoy, 2009). Considering both these data about Ardi and the data that you took, revise your hypothesis. (1 point) Explain chimpanzee skull and/or skeletal development, in terms of regulatory genes (specifically, timing), in light of your new hypothesis. (0.5 points)   Explain Homo sapiens skull and/or skeletal…
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