Humans are unable to safely consume raw meat due to biological differences between humans and other meat-eating animals. Cooking meat before eating provides significant health benefits and protection against foodborne illnesses for humans. Below we will explore why humans evolved without the ability to eat raw meat, what dangers are presented by consuming raw meat, and how cooking meat allowed early humans to access more nutrients and progress as a species.
The Evolution of the Human Digestive System
Humans evolved as omnivores, consuming both plant and animal matter, rather than true carnivores which subsist primarily on meat. True carnivores such as lions have digestive systems optimized for consuming raw meat. Their stomachs are highly acidic, with a pH of 1-2, which kills any pathogens that may be present in raw meat. Saliva in carnivorous animals also contains antibacterial compounds. In addition, carnivores have short intestinal tracts, which allows meat to pass through the body rapidly before bacteria have time to proliferate.
Humans, on the other hand, evolved very differently. The human stomach has a pH between 4-5, which is not high enough to kill all meat-borne pathogens. Human saliva also does not contain compounds to inhibit bacterial growth. Finally, the human small intestine is over 23 feet long, which allows plenty of time for bacteria to multiply if infected meat is consumed. So while humans evolved the ability to digest cooked meat and access its nutrients, we lack the specialized digestive system of carnivores to consume it raw and safely.
Examples of Differences Between Human and Carnivore Digestive Systems
| Animal | Stomach pH | Saliva Antibacterial Compounds? | Small Intestine Length |
|---|---|---|---|
| Lions | 1-2 | Yes | Approx. 25 feet |
| Humans | 4-5 | No | Approx. 23 feet |
Dangers of Eating Raw Meat for Humans
Consuming raw or undercooked meat exposes humans to a number of pathogens that can cause severe food poisoning. These include:
- Salmonella – Salmonella infections cause diarrhea, fever, abdominal cramps that can last for days. May become life-threatening in individuals with weakened immune systems.
- E. coli – Can cause bloody diarrhea, severe stomach cramps, and vomiting. Potentially life-threatening complications include kidney failure.
- Campylobacter – Leads to diarrhea, cramping, abdominal pain, and fever within 2-5 days after infection. Typically lasts 1 week. Can spread to bloodstream and become life-threatening.
- Listeria – Causes fever, muscle aches, nausea. Can infect the bloodstream and brain. Particularly dangerous for pregnant women, newborns, elderly and immunocompromised.
- Trichinella – Parasitic roundworms that can infect muscle tissue after ingesting infected raw meat. Causes diarrhea, abdominal pain, nausea, fatigue.
These bacteria are present in the digestive systems of animals and contaminate meat during slaughter. Eating undercooked pork, chicken, and other meats thus exposes humans to these pathogens before our stomach acid has a chance to kill them. While animals like lions can safely ingest contaminated raw meat, humans lack the proper biological defenses.
Reported Cases of Food Poisoning in United States Each Year
| Pathogen | Estimated Cases |
|---|---|
| Salmonella | 1.35 million |
| E. coli | 265,000 |
| Campylobacter | 1.5 million |
| Listeria | 1,600 |
Consuming raw or undercooked meat is the leading cause of these foodborne illnesses, which sicken millions of Americans each year. Proper cooking is necessary to protect consumers against exposure to these bacteria.
The Protective Effects of Cooking Meat
Cooking meat before eating provides a number of health protections:
- Kills harmful bacteria – Heat above 160°F denatures proteins in pathogens and destroys them. This makes meat safer to eat.
- Parasite destruction – Freezing, cooking, or irradiation kills parasites like trichinella present in raw meat.
- Improves digestibility – Heat partially breaks down proteins like collagen in meat, making cooked meat easier to chew and digest for the human gastrointestinal system.
- Inactivates harmful compounds – Cooking meat reduces levels of heat-sensitive toxic compounds like hydrazine, making it safer for consumption.
The main purpose of cooking meat is to kill off pathogens that can accumulate during slaughter and processing. Humans lack the specialized biology to consume contaminated raw meat safely. Cooking provides a complete barrier against most disease-causing microbes that may be present.
Minimum Safe Cooking Temperatures for Meat
| Meat | Minimum Safe Temperature |
|---|---|
| Beef, Pork, Lamb, Veal | 145°F |
| Chicken, Turkey, Duck | 165°F |
| Fresh Ham | 160°F |
| Fish | 145°F |
Cooking meat to these minimum safe temperatures measured with a food thermometer kills pathogens and makes the meat safe for human consumption.
The Evolutionary Advantages of Cooking Meat for Early Humans
When early humans began controlling fire over 1 million years ago, cooking meat provided evolutionary advantages:
- Increased nutrient absorption – Cooking makes protein and carbohydrates more digestible, allowing more efficient nutrient absorption from meat.
- Killed foodborne illnesses – Allowed humans to access nutrient-dense meat more safely by killing pathogens.
- Supported brain growth – The higher calorie intake and better nutrient absorption from cooked meat may have supported the development of larger, more energetically-demanding human brains.
- Improved mastication – Cooking softened meat fibers, requiring less forceful chewing from flat human molars not well-suited to raw meat.
Access to cooked meat proteins and fats was likely a key factor in human evolution. The additional nutrients supported the metabolic needs of larger brains, while cooking killed the pathogens found in raw meat that human digestive systems were not adapted to handle.
Increase in Human Brain Size Over Evolutionary History
| Species | Estimated Brain Size |
|---|---|
| Australopithecus | 400-500 cc |
| Homo habilis | 500-800 cc |
| Homo erectus | 750-1250 cc |
| Modern Homo sapiens | 1200-1750 cc |
The increase in brain size as humans evolved likely depended on the consumption of nutrient-rich, cooked meat which could be safely digested and absorbed.
Conclusion
Humans cannot safely consume raw meat because we evolved very different digestive systems compared to pure carnivores. Our stomach acid and saliva is ill-equipped to kill off the bacteria that contaminate fresh meat during slaughter. Eating raw meat exposes humans to foodborne pathogens that can cause serious illnesses. Cooking meat at safe temperatures denatures these pathogens, making the meat safe for human consumption. It also increases digestibility and nutrient absorption. The advent of cooking meat was a key evolutionary development that likely supported the growth of larger human brains by allowing access to nutrients in meat that could not be safely consumed raw. So while cooking meat takes more time, it transformed human evolution and remains essential for avoiding foodborne illnesses.