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Not all animals have neurons; Trichoplax and sponges lack nerve cells altogether. Neurons may be packed to form structures such as the brain of vertebrates or the neural ganglions of insects. The number of neurons and their relative abundance in different parts of the brain is a determinant of neural function and, consequently, of behavior.
Animal ability to process and respond to stimuli is correlated with brain size. Small-brain animals tend to show simple behaviors that are less dependent on learning than those of large-brained animals. Vertebrates, particularly mammals, have larger brains and complex behavior that changes with experience.
Yet their brains share several characteristics revealed by recent anatomical, molecular, and ontogenetic studies. [55] [56] [57] Vertebrates share the highest levels of similarities during embryological development, controlled by conserved transcription factors and signaling centers, including gene expression, morphological and cell type ...
Of course, animals that are not vertebrates also have brains, and their brains have undergone separate evolutionary histories. [ 6 ] The brainstem and limbic system are largely based on nuclei , which are essentially balled-up clusters of tightly packed neurons and the axon fibers that connect them to each other, as well as to neurons in other ...
Brains of an emu, a kiwi, a barn owl, and a pigeon, with visual processing areas labelled. The avian brain is the central organ of the nervous system in birds. Birds possess large, complex brains, which process, integrate, and coordinate information received from the environment and make decisions on how to respond with the rest of the body.
Orcas are social animals that live in family pods with up to 40 members, but Kiska has lived alone in a small tank since 2011. In decades of studying the brains of humans, African elephants ...
Cephalization is a characteristic feature of the bilaterians, a large group containing the majority of animal phyla. [3] These have the ability to move, using muscles, and a body plan with a front end that encounters stimuli first as the animal moves forwards, and accordingly has evolved to contain many of the body's sense organs, able to detect light, chemicals, and gravity.
The human brain has evolved around the metabolic, environmental, and social needs that the species has dealt with throughout its existence. As hominid species evolved with increased brain size and processing power, the overall metabolic need increased. Compared to chimpanzees, humans consume more calories from animals than from plants.