Question

The defining trait of hominins is _________ a. tool use b. bipedalism c. a large brain d. endothermy

Short answer

The defining trait of hominins is bipedalism.

Step-by-step solution

Understand the Definition of Hominins

Hominins are a group of species that includes humans and their ancestors, who have a set of traits distinguishing them from other primates.

Identify Key Traits of Hominins

To identify the defining trait, we list key traits associated with hominins. These include bipedalism, increased brain size, use of tools, and other physiological adaptations.

Determine the Defining Trait

Out of the listed traits, bipedalism refers to the ability to walk upright on two legs. It is the most distinguishing feature of hominins that first emerged in early members of the group.

Eliminate Other Options

- Tool use (a) is a significant trait but not unique to hominins, as some non-hominin species also use tools. - A large brain (c) developed later in the evolutionary history of hominins. - Endothermy (d) is a characteristic of all mammals, not just hominins.

Key concepts

Bipedalism

Bipedalism is the ability to walk upright on two legs, and it is a hallmark of human evolution. This trait sets hominins apart from other primates. Bipedalism allowed our ancestors to move over long distances and freed their hands for other tasks.

The development of bipedalism brought several anatomical changes:

• The pelvis became shorter and broader, supporting an upright posture.
• The spine developed a distinct curvature to help balance the head above the body.
• The feet evolved with arches for shock absorption, assisting in walking efficiency.

These adaptations did not happen overnight but rather gradually over millions of years, contributing significantly to the survival and success of early hominins.

Primate evolution

Primate evolution is a comprehensive process that has led to the emergence of human beings. It involves the transformation of species over millions of years, from ancient primate-like animals to modern humans.

Early primates shared common traits such as large brains and forward-facing eyes, which are useful for depth perception. They lived in trees and had flexible limbs and hands suitable for grasping branches. Over time, environmental changes prompted some primate species to adapt to new habitats. This adaptation process eventually led to bipedalism, diverse diets, and the development of complex social structures.

The evolutionary tree of primates includes several branches; while some resulted in species like gorillas and chimpanzees, others led to human ancestors, highlighting the rich diversity and adaptability of primates throughout history.

Human ancestors

Human ancestors, also known as hominins, are species that have evolved on the lineage leading to humans after diverging from the common ancestor shared with chimpanzees. This group is characterized by bipedalism and a gradual increase in brain size over time.

Hominins include several extinct species, such as Australopithecus and Homo habilis. Each of these species has contributed uniquely to the path of human evolution:

• Australopithecus: Known for their remarkable adaptations to both climbing and walking, they exhibited a mix of tree-dwelling and bipedal behaviors.
• Homo habilis: Often credited with being one of the earliest users of stone tools, marking significant behavioral advancement.
• Homo erectus: Known for their dramatic increase in brain size and the use of fire, indicating a leap in cognitive abilities and survival strategies.

Understanding these ancestors helps us learn how humans have adapted physically and behaviorally to changing environments over millennia, showcasing the resilience and ingenuity inherent in the human lineage.