Introduction
A human being is a living member of the species Homo sapiens, distinguished by a unique mix of physical, cognitive, and social traits. This article explores how humans fit into the animal kingdom, the anatomical and neurological features that enable upright walking, language, and culture, and the measurable traits that help define modern humans. The primary keyword for this piece is “what makes a human,” which appears early to match search intent and guide readers.
Where humans fit in the animal kingdom
Humans are animals—mammals, primates, and members of the great ape family. Our species likely descended from Homo heidelbergensis and shares close ancestry with Neanderthals. Anatomically modern humans emerged in Africa about 300,000 years ago and later dispersed globally. Genetically, humans share roughly 98.7% of DNA with chimpanzees; the small genetic differences have outsized effects on brain development, skeletal form, and behavior, producing the distinct species we are today.
Anatomy adapted for upright walking
Bipedalism is a defining physical feature that shaped many aspects of human anatomy.
- Pelvis: Short, wide, bowl-shaped hip bones stabilize each step and support internal organs. A distinctive projection, the anterior inferior iliac spine, provides attachment for ligaments and muscles needed for upright hip flexion.
- Gluteal muscles: Shifted to prevent pelvic drop during single-leg stance, enabling efficient walking and running over long distances.
- Foot structure: A permanent arch functions like a spring, and an aligned big toe aids propulsion rather than grasping.
- Skeletal lightening: Compared with earlier hominins, modern humans have lighter bones suited for endurance and agility.
These adaptations underpin humans’ unique ability among great apes to travel long distances efficiently on two legs.
The human brain and cognition
The human brain is larger and organized differently than that of other primates.
- Size and development: The average human brain volume (~1,300 cubic centimeters) is about three times that of a chimpanzee. During fetal development, brain progenitor cells proliferate for longer and at a higher rate, delaying specialization and allowing more neurons to form.
- Genetic drivers: Genes such as ARHGAP11B promote production of brain progenitors; other human-specific gene sets increase neuronal output. These molecular differences contribute to an enlarged cerebral cortex with extensive neural circuitry.
- Functional consequences: The expanded cortex supports advanced reasoning, long-term planning, abstract thought, and the complex motor control needed for speech.
Together, these features form the biological basis for sophisticated cognition and problem solving.
Language and symbolic thought
Human language is recursive and symbolic, enabling communication of infinitely varied ideas.
- Recursion: Humans can embed clauses and ideas within other ideas, producing sentences of virtually unlimited complexity.
- Symbolism: Words are arbitrary symbols; speakers learn shared conventions that map sounds or signs to concepts (for example, the word “tree” represents the concept of a tree).
- Genetic and neural basis: Genes like FOXP2 affect circuits needed for coordinated speech, but language arises from interactions among many genes, brain structures, and social learning.
- Cultural accumulation: Language allows teaching, recording, and accumulating knowledge across generations—an essential mechanism for cumulative culture and technological progress.
Language is central to what makes humans capable of evolving culture and science.
Social life, culture, and cumulative innovation
Humans are intensely social and culturally inventive, distinguishing them from other animals.
- Social structures: Humans form bonds from small families to nations. Earlier estimates suggested meaningful relationships for about 150 people, but cultural tools—kinship systems, rituals, writing, and digital networks—extend our social reach well beyond brain-size limits.
- Cumulative culture: Humans build on previous innovations in a ratchet-like fashion. Small improvements can compound over generations—leading from stone tools to engines and airplanes.
- Cooperative institutions: Shared norms and institutions (legal systems, markets, educational systems) magnify cooperative capacity and coordinate large-scale projects.
These cultural capacities allow humans to transform environments and create complex societies.
Measurable human traits and variation
Several numeric metrics help describe human biology, while also highlighting variation.
- Genome size: About 3 billion nucleotide base pairs per haploid genome (roughly 6 billion in diploid cells).
- Body temperature: The classic 37.0°C (98.6°F) is outdated; large studies place the average nearer 36.1°C (97.0°F), with individual and daily variation.
- Life expectancy: Global life expectancy rose from 66.8 years in 2000 to 73.1 years in 2019, then dipped during the COVID-19 pandemic. Variation remains large between regions due to healthcare, sanitation, and nutrition.
- Physical differences: Modern humans have lighter, more gracile skeletons, smaller teeth, and reduced facial projection compared with archaic humans. Reduced jaw size correlates with dietary changes such as cooking, practiced for at least several hundred thousand years.
- Thermoregulation and body hair: Relative hairlessness and abundant sweat glands support efficient cooling, aiding endurance activities and heat tolerance.
These metrics show both shared human features and wide population-level diversity.
What makes humans physically distinct from other species
A combination of traits—rather than a single defining feature—makes humans distinct.
- Integrated anatomy for endurance bipedalism and tool use.
- Enlarged, highly plastic brain supporting abstraction, planning, and language.
- Capacity for complex symbolic communication and cumulative culture.
- Social systems and institutions that extend cooperation across large groups.
- Technological ability to reshape ecosystems and build external knowledge stores.
This constellation of anatomical, cognitive, and social traits creates the distinctive niche humans occupy.
Legal and social recognition
In law, a human being is typically defined as a “natural person,” a category that confers rights and responsibilities distinct from “artificial persons” like corporations. This legal distinction matters across constitutional law, contract law, and human rights frameworks.
Examples and implications
- Evolutionary example: Small genetic changes (for example, gene variants affecting brain progenitor proliferation) amplified over time lead to major cognitive and anatomical differences between humans and other apes.
- Cultural example: The invention of writing and record-keeping allowed societies to store knowledge externally, accelerating complex administration, law, and science.
- Public-health implication: Improvements in sanitation, vaccines, and nutrition—not changes in human biology—drove most of the 20th-century gains in life expectancy.
Understanding what makes humans helps explain both our biological limits and our extraordinary capacity for cultural and technological change.
References
- Stringer, C. (2016). The origin and evolution of Homo sapiens. Proceedings of the National Academy of Sciences.
- Hublin, J.-J., et al. (2017). New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature.
- Ardila, A., et al. (2020). The evolving human brain: Gene regulation and expansion. Trends in Neurosciences.
- Lieberman, D. E. (2015). The Story of the Human Body: Evolution, Health, and Disease. Pantheon.
- World Health Organization. Global health estimates and life expectancy data.
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