What do rats lack? - briefly
Rats cannot vomit because they lack a functional emetic reflex. They also lack sweat glands on most of their body, relying on panting and limited foot pads for thermoregulation.
What do rats lack? - in detail
Rats possess many traits common to mammals, yet several physiological, anatomical and cognitive capacities are absent or under‑developed.
Rats do not have a true vocal‑learning system. Their vocalizations are innate, lack the flexibility of human speech, and cannot be altered through imitation. Consequently, they are unable to acquire complex spoken language or produce phonetic variations beyond species‑specific calls.
The prefrontal cortex of rats is rudimentary compared to that of primates. This region shows limited expansion, resulting in reduced capacity for abstract reasoning, long‑term planning and self‑monitoring. Behavioral experiments reveal that rats can solve simple mazes but fail when tasks require multi‑step strategizing or reversal of learned rules.
Metabolic pathways for synthesizing vitamin C are missing. Rats, like most mammals, lack the functional gene for L‑gulonolactone oxidase, rendering them dependent on dietary intake for this antioxidant. Humans share this deficiency, but many other vertebrates retain endogenous production.
Certain immune components are not present. Rats lack the complement protein C5a receptor 2 (C5aR2) found in humans and some other mammals, influencing the regulation of inflammatory responses. This absence can alter susceptibility to specific pathogens and modulate the outcome of experimental disease models.
Rats are incapable of generating high‑density lipoprotein (HDL) particles with the same apolipoprotein composition as humans. Their HDL particles contain a predominance of apoA‑I and lack significant amounts of apoA‑II, affecting cholesterol transport efficiency and modeling of atherosclerosis.
The visual system exhibits limitations. Rats are dichromats, possessing only two types of cone photoreceptors, which restricts color discrimination to the blue‑green spectrum. Human trichromacy provides a broader color palette and finer visual acuity.
In summary, rats lack:
- Vocal learning and complex speech production
- An extensively developed prefrontal cortex for higher‑order cognition
- Endogenous synthesis of ascorbic acid (vitamin C)
- The complement receptor C5aR2 in the innate immune cascade
- Human‑like HDL apolipoprotein composition
- Trichromatic vision and high visual acuity
These deficiencies shape the suitability of rats as model organisms and define the boundaries of their physiological and behavioral capabilities.