multiseluler

Multiseluler, or multicellular, describes organisms composed of two or more cells that adhere to one another, communicate, and depend on cell differentiation to perform specialized functions. In true multicellularity, cells rely on a coordinated development program and an extracellular matrix. This organization enables division of labor, increased body size, and complex life cycles, while requiring regulated growth, reproduction, and cell death.

Multicellularity arose independently in several lineages, including animals (metazoans), plants, and fungi, as well as some algae. The earliest multicellular forms appeared around 1.2-1.5 billion years ago in simple assemblies of identical cells; later lineages evolved differentiated tissues and organs. Key innovations include cell adhesion molecules, gap junctions or equivalent signaling pathways, and extracellular matrix components.

Most multicellular organisms display tissue-level organization: in animals, tissues such as epithelium, muscle, nerve; in plants, dermal, ground, and vascular tissues; in fungi, networks of hyphae. Some algae and many protists exemplify true, integrated tissues. A related concept is colonial life, where unicellular organisms form aggregates; but true multicellularity typically implies irreversible cell differentiation and developmental programs.

Advantages include increased organismal size, specialization, redundancy, and environmental adaptation; challenges include cellular cooperation, development, and vulnerability to systemic failure. Multicellularity remains a major topic in evolutionary biology and developmental biology, with ongoing debate about the steps and genetic innovations that enable it.