Short intro: Cooking food is a unique human activity spanning across all cultures, and humans appear to be evolutionarily adapted to this crucial aspect of their diet (Wrangham and Conklin-Brittain2003). The value of cooking lies in its ability to widen the range of foods that are safe to eat (whether by making their digestion easier or neutralizing toxic compounds) as well as extract more energy from the foods ingested. Both human and animal studies illustrate that the more cooked food there is in a diet, the greater the net energy gain for the eater (Carmody and Wrangham2009), and a diet of raw foods is energetically inadequate even when various nonthermal processing methods are employed (Koebnick et al.1999). The effect of cooking on the energy gain from eating includes several mechanisms: increasing digestibility and thus caloric value of ingested foods, lowering the body’s energetic costs of digesting, and mounting an immune defense against food pathogens.
I went to a great talk at ASU’s Evolution & Medicine center, where Dr. Stearns from Yale University discussed tradeoffs 🙌🎓. I’d love to invest the rest of this day into summarizing what i’ve learned but i’ve got a dissertation to write, jobs to apply to, etc. etc… So a really short science communication bit is all i can manage!
Short version: Look at this chart.. It shows how mental illness is a result of a conflict between paternal and maternal genes. Notice how autism and szchisophrenia manifest most at the extremes of a newborn’s birth weight.
Long version: “Imprinted brain theory” argues that maternal & paternal set of genes might have antagonistic reproductive interests: father “turns off” genes that down-regulate fetal growth, resulting in enhanced growth. Mother turns on these genes, inhibiting growth.. Both actions result in normal range of weight of the newborn.
The mother is 50% related to each of her offspring.
The logic behind conflicting interests from the parents is such: since a father is uncertain that a woman’s other and future children will be his, it may be in the father’s reproductive interest for his child to use mother’s resources MORE, while the mother’s interest (considering she’ll be 50% related to all her current and future children equally) is to limit this and have resources for future kids. With polygamous mating, offspring’s genes from the father will be selected to extract MORE from the mother, and maternal genes will be selected to resist such increased extraction of bodily resources.
To simplify: father needs current baby to use up as much of mother’s resources to grow bigger/stronger/have higher chance of future reproductive success because he can’t be sure her other kids will actually be his.
A conflict arises when action of one parent is cancelled by disrupting imprinting- so disruption of maternal interests would result in an uninhibited expression of paternal interests. Such disruptions result in abnormally low or high birth weight (along with other factors such as behavioral aspects- the extremes of which are considered mental illnesses). Extreme genomic imprinting in favor of MATERAL genes will result in lower birth weight, and is argued to cause psychosis (schizophrenia spectrum) while the opposite causing autism spectrum disorders. The chart above shows how such abnormalities in weight are indeed associated with autism & schizophrenia.
It’s taking me awhile to “digest” all the information (hehe), but I found the seminar fascinating and wanted to summarize some main points. Lots of open questions remain, but John Pepper of National Cancer Institute really shows how examination of any health problem needs to focus not only on proximate causes, but the ultimate or evolutionary causes.
So.. Pepper asks- why is mammal meat bad for humans, specifically?
In humans, red meat (he refers to it just as mammal meat) is linked to inflammatory diseases (cardiovascular, alzheimer’s, arthritis). What’s the mechanism behind this?
The inflammation from mammal meat has to do with our antibodies attacking something coming from other species.. When we eat mammal meat, we in fact incorporate something non-human from the diet- sialic acid.
Both human and other mammals have sialic acid in their tissues, actually, but humans have a unique mutation that replaces the form found in other mammals (ancestral form- Neu5Gc) with a different one- uniquely human (Neu5Ac).
So.. if we eat meat we get the new aquired ancestral sialic acid, it becomes part of our cells, and the small structural differences in the two get recognized by the immune system.. which responds with a defense- inflammation!
Chimpanzees are humans’ closest evolutionary relatives, sharing a common ancestor 6–7 million years ago..
WHY does human sialic acid differ uniquely? The “Malaria hypothesis” (see Martin&Rayner, 2005) proposes that in Africa, early humans escaped from the ancestral pathogen they shared with chimpanzees. They managed to do so by replacing the pathogen’s binding target (ancestral sialic acid Neu5Gc) with novel Neu5Ac. With time, a population of that old evaded pathogen evolved to infect humans again by recognizing the new Neu5Ac..leading to the origin of malaria.
If the Malaria Hypothesis explains why the initial change in humans happened.. why has it remained the same to this day? I mean, it’s been some several million years now- has this mutation been advantageous this whole time? It’s an important question because this sialic acid mutation poses a COST on our health: this trait causes chronic inflammation in people who eat mammal-derived foods + it also now causes vulnerability to malaria.
The hypothesis for why the human sialic acid modification is still around is that it
provides benefits- specifically, protection from parasites and pathogens via increased inflammation. This is relevant because of what humans have been doing for the last ~15,000 years. Animal domestication!
Humans are more vulnerable to shared pathogens from other mammals (than from non-mammals). So being around cattle, for example, carries a risk of catching pathogens from which that cattle suffers. Such animal pathogens impose a strong selective pressures on humans.. Pepper suggests that the uniquely human sialic acid (Neu5Ac) allows our diet to adapt us to the issue of animal pathogens by adjusting our inflammatory tone (how much inflammation we are experiencing): “those human populations that are exposed to domesticated food-mammals and their pathogens are also eating mammal-derived foods that are pro-inflammatory (both meat and dairy).”
Inflammation is a great example of a trade-off. It both has benefits (protection from parasites & infections) and costs (chronic disease, metabolic expense of mounting an immune response). The optimal balance for this trade-off would depend on how strong of a pathogen pressure you’re experiencing.
This increases inflammatory PROTECTION only where it’s most needed (like around animals). So this auto-immune inflammation from mammal foods in the diet not only increases likelihood of chronic disease, but protects against shared mammalian pathogens.
….. …… ……
It got me thinking about human culture and our ability to modify our environment in all sorts of ways- an example of “maladaptation” to modern times! Living in cities, not exposed to higher pathogen load from being around domesticated animals..yet having access to all the mammal meat we can buy = all put you in a situation where the good old sialic acid mutation might do more harm than good. Should people go vegan? Should they simply cut down on red meat? There was no discussion on the effect size of mammal meat eating and chronic disease, so I wouldn’t necessarily jump onto any lifestyle changes based on this talk. Yet the process of understanding this health concern through the lens of evolutionary medicine is quite fascinating!
P.S. I’m not an expert on this topic. If you have something to correct or add, please comment 🙂
Got it- to FAST? 😀
The past week has been a treat in terms of great talks on campus. At ASU we are super-lucky to have the Center for Evolution & Medicine, which holds weekly talks by amazing speakers.
When I saw that the upcoming seminar was related to diet and eating..or more specifically NOT eating or “dietary restriction”, I of course RSVPd in a heartbeat.
“Eat breakfast yourself, share dinner with a friend, give the supper to your enemy”- Russian Proverb
I’ve been in fact fascinated with caloric restriction for years now (I wrote a whole research paper on it in the first year of my master’s degree). You might have heard of intermittent fasting (e.g. popular in the CrossFit world), or the CR Society ( http://www.crsociety.org/ )- all are related to the concept that restricting food intake results in health benefits (from extending life to preventing and reversing disease).
I’m sure you can Google caloric restriction and find a bunch of information on its reported benefits..you would see this chart at the CR society website- the lifespan of calorie-restricted (CR) mice vs non-CR mice. You can see that those whose food intake was restricted by more & more % lived longer. Why do many animals (and perhaps humans) appear to be so well-adapted to eating less? The traditional interpretation of this CR phenomenon is that the dietary restriction effect “has evolved as a way to enhance survival & preserve reproduction during periods of naturally occurring food shortage”. In other words- being adapted to do well on restricted food intake during rough times would have helped our ancestors survive them & stay healthy to have kids later when the food situation improves.
The traditional interpretation of this CR phenomenon is that the dietary restriction effect “has evolved as a way to enhance survival & preserve reproduction during periods of naturally occurring food shortage”.
Experimental evidence with animals, however…supports a different hypothesis- the one Dr. Austad (Professor & Chair of the Department of Biology at the University of Alabama) presented to us last week. Again, I wouldn’t be able to cover everything he discussed during the seminar, but I do want to highlight a couple of main points!
I. First, even though the first book on dietary restriction (DR) dates back to the late 16th century, we still do not know the mechanism behind why DR seems to extend life and vigor in animals + delay disease such as cancers. METABOLISM was the original suspect, as metabolic rate goes down with fasting.. however, metabolic rate drops initially yet gradually goes back UP (takes 6-8 weeks to happen).. Since DR changes an unbelievable amount of physiological parameters (see screenshot ->) it is very hard to determine its mechanism.
II. Second, while many sources cite mice experiments showing life extension with caloric restriction.. those experiments are done with lab mice. When DR studies are done with wild mice, DR has no effect on longevity. WHAAAT!! I’ve never heard this before- in fact i was under the impression that CR/DR extends life in animals, period. Well, NO STUDY has ever found that DR extends life or improves health in nature (or even “nature-like” conditions). Mice in the wild actually do not have enough fat stores to reduce feeding except very briefly (wild mice has about 4% fat while a regular lab mice has 15%; also lab mice do not reproduce). In fact, mice in nature simply do not live long enough for the survival benefits of DR to be important. Another challenge to the original hypothesis that adaptation to dietary restriction enhances survival, is that DR increases mortality from some infections. Lastly, DR increases cold sensitivity (and cold is a major source of death in wild mice) and slows down wound healing.
Sounds like animals in the wild would not benefit from adaptation to dietary restriction… yet why is the positive DR effect observed in so many studies so common?
III. Well, even though wild mice do not live longer with restricted diets, DR still results in cancer protection for them. But even more importantly, DR has been found to protect against acute effects of many many toxins! Dr. Austad talks about this discovery in the following way:
.. if animals can not afford to wait to reproduce..and they have to do it even when food conditions are poor, what they will do is broaden their diet. This means they might be ingesting a lot of toxins they are not normally exposed to (foods infected with fungi, new seed types that are well defended by the chemicals they wouldn’t normally encounter). So the hypothesis is that DR acutely induces broad defense mechanisms from a broad range of toxins
Toxicology studies have shown that mice that are calorically restricted survive a wide range of toxins. DR also acts as an acute (vs. chronic) protectant against other problems (see slide below). Renal ischaemia reperfusion injury (IRI) is a common cause of acute kidney injury and we can see that while ad libitum mice are dying steeply by day 7, those on DR of various proportions survive (30% DR is only 70% of normal food intake; ad libitum stands for eating as much as one wants). This is quite impressive!!!
These acute benefits of DR have very important implications. We can think about these effects actually protecting the body against the toxins it itself produces (like free radicals).. it also has clinically relevant advantages- e.g. patients on very strong drug cocktails fasting to avoid harsh side-effects. This suggests that the protective effects of DR could have clinical relevance unrelated to chronic benefits like life extension.
The new hypothesis explaining the evolutionary advantage of this paradoxical effect is that dietary restriction arose as a defense against novel exposure to toxins during food shortage.
So in conclusion.. we saw evidence suggesting that dietary restriction would NOT enhance survival in nature. Yet research has shown that DR increases health and life in a diversity of species. The new hypothesis explaining the evolutionary advantage of this paradoxical effect is that dietary restriction arose as a defense against novel exposure to toxins during food shortage.
My conclusion? I’m still excited about this topic- more than ever before!!! There is a lot of work done now on the timing of food intake as well (not just restricting the amount, but restricting the timing of eating and human health) and I can’t wait to post more about this (after I collect some necessary data though :). Watch out for early May as I’ll be sharing some more info!
This week on ASU campus I managed to attend a fascinating talk: Reconsidering the Role of Plant Foods in Hominin Diets by Dr. Chelsea Leonard.
It was a job talk for the Evolutionary Anthropology department here at ASU and Dr. Leonard is an evolutionary ecologist interested in “human foraging decisions & diet reconstruction”(so- her work would help to clarify what humans ate in the past!) working with Twe populations in Namibia (southwest Africa).
Why does Dr. Leonard study the role of plants? Since shifting towards more meat in diets of early humans has been suggested to be crucial for the unique adaptations in our genus (e.g. large brains), animal foods appear to be very important. There is indeed a strong case for meat in a human diet- in comparison to chimpanzees who are mostly herbivorous (eat plants), the human gut has opposite proportions- our small intestine is much longer, while the colon is a lot shorter. The colon is where fiber fermentation occurs- something crucial if you are eating lots of plant foods (and wild plant foods are very high fiber!). What Dr. Leonard suggests, though, is that meat’s importance in human diets may be quite overstated (especially in meat-heavy “paleo” diets popular now).
The people she studies- Twe- are “forager-horticulturalists”; while the Namibian government has been providing maize for them (this started very recently, in the last 7 yrs or so), they mostly forage for wild foods and have very low intake of animal products. Apparently, historically this population hunted large game and had a higher meat intake.. but the area is very poor in large animals now (and has been this way for ~200 yrs).
While I wont’ be able to describe everything Dr. Leonard discussed, I found the following fascinating.. Based on her observations and interviews with the Twe, she constructed and analyzed a hypothetical (yet realistic) diet for this region. Since Twe seem to be doing just fine health-wise with an extremely low animal food intake (there might be some birds, insects, rodents eaten from time to time), she wanted to test if their meatless diet truly meet basic nutritional requirements.
Based on the plants the Twe regularly eat, her analysis showed that such meatless diet can realistically provide enough protein (it can reach minimum levels of essential amino acids our body can not produce without foods that contain them), it can also provide enough fat (while most plant sources were extremely low in fat, the grass seeds often eaten are rather high in it). The main issue with this meatless diet was calories. Getting enough calories to survive would be improbable : while the hypothetical food intake reaches 1774 calories a day.. only 772 of them are metabolized. What this means is that a lot of these calories are not available to the human body- since humans can not ferment fibers very efficiently, a lot of this rough wild plant fiber is indigestible and does not provide our body with energy.
The main issue with this meatless diet was calories.
Since foraging for wild plants is very labor intensive (and this does not really mean standing around picking berries, but e.g. digging up roots that are about 1 meter (~40 inches) into the ground, or grinding grass seeds and cooking them into porridge), there isn’t enough time in a day to get enough digestible calories from foraging. So animal products are more efficient and provide a concentrated mix of not only essential nutrients, but fat, protein, and calories. While the speaker couldn’t quite estimate the % of calories coming from small game (the birds, insects, etc.), it was very small but still was a part of this population’s diet [note: any time honey was available, it was eaten in large amounts and rather adored, apparently!]. Thus, while a vegetarian diet can be maintained in our modern world with plentiful food supply (and supplementation), it was not possible for non-industrialized populations.
humans are highly adaptable as we span huge geographical areas, and thus no single “diet” “made us human”
We know humans are highly adaptable as we span huge geographical areas, and thus no single “diet” “made us human” (thus, there is no one Paleo Diet). Yet plants are extremely important in our history- we see that they can sustain populations in good health to a very large degree. One issue with studying the role of plants in human diets is that they do not last well archeologically (e.g. it’s much easier to find evidence of large game being consumed, because their remains last well).
while a vegetarian diet can be maintained in our modern world with plentiful food supply (and supplementation), it was not possible for non-industrialized populations.
Overall, this was a really great talk! It also reminded me of a paper I read on the significance of plant foods in human evolution, which I talked about HERE.
[note: if you are an evolutionary anthropologist sand have any edits/clarifications to my post, please comment! I am not an evolutionary anthropologist :)]
Note: This Fall I decided to attempt even more science communication! The Sci Files (imagine the x files theme playing) will be a collection of health & food-related research articles that I summarize in plain(er) language. I became quite passionate about breaking down hard-to-understand research for the public audience and I’ll try to do my best, considering I’m no expert! Yet 5 years of graduate courses- statistics, research methods, nutrition psychology, evolution & medicine- at least give me skills to understand a lot of the material that might be overwhelming to a lay reader. I will try to keep the summary to one page (~500 words), possibly followed by extra material that could be interesting 😉
For the first Sci File, i’m looking at a paper discussed yesterday during a lecture on the paleolithic diet. It’s published in 2015 in The Quarterly Review of Biology and the title intrigued me “The Importance of Dietary Carbohydrate in Human Evolution”. I’ve heard multiple talks on how the various “paleolithic” diets could have included starchy foods, but I didn’t think they were substantial parts of such diets. Original paper: Hardy, K., Brand-Miller, J., Brown, K. D., Thomas, M. G., & Copeland, L. (2015). The importance of dietary carbohydrate in human evolution. The Quarterly Review of Biology, 90(3), 251-268.
The authors propose that carbohydrates- particularly cooked high starch plant foods like tubers & roots- were essential in the evolution of our species- especially for the quick expansion of the human brain. They support this by showing that (1) critical development of this large glucozse-hungry organ required digestible carbohydrates, and eating cooked starch would really increase this energy availability to the brain (+ other glucose-hungry tissues such as red blood cells and the developing fetus).
They also show that the mutation in the enzyme for digesting carbs (salivary emylase, AMY1) co-evolved with both cooking and eating starchy carbs, giving an advantage to early humans. To put it in simpler terms: carbs were quite important, as shown in our increased ability to digest cooked starch (otherwise, why retain this mutation if we did not rely on cooked starches for a substantial amount of time?). A meat-heavy diet wouldn’t have provided sufficient glucose or energy to the growing brain + 1) large amounts of protein are in fact toxic and 2) providing sufficient amount of animal-based food would require too much effort:
“the energy expenditure required to obtain it may have been far greater than that used for collecting tubers from a reliable source”
There is no clear agreement on what constituted a “Paleolithic diet”, but it makes sense to assume that our current physiology should be optimized to the kind of diet we had during our evolutionary past. Some important features in our evolution are considered linked particularly to key changes in diet: smaller teeth, smaller digestive tract (1.8 mln years ago), larger brain size (began ~2 mln yrs ago; accelerated around 800,000 yrs ago), and better aerobic capacity (ability of the heart and lungs to get oxygen to the muscles) about 2 mln years ago.
Early hominins include modern humans, extinct human species, and all our immediate ancestors
Some have argued that these changes happened because humans transitioned from a diet based on fibrous plants to mostly meat-based diets.. But this paper offers evidence that both plant carbohydrates (carbs) and meat were crucial in human evolution. In their words:
“We contend that in terms of energy supplied to an increasing large brain, as well as to other glucose-dependent tissues, consumption of increased amounts of starch may have provided a substantial evolutionary advantage to Mid-to-Late Pleistocene omnivorous hominins“.
Actual physical remains of early hominins are quite rare, so there is a lot of uncertainty about their lives. As already mentioned, there were several important changes in hominin morphology (size,shape,andstructure of an organism) related to the appearance of Homo erectus (teeth, digestive length, brain). Anthropologists propose that they occurred with a change from a “high-volume, low-energy diet” (lots of fibrous plant material that’s not very calorie rich), to a low-volume, high-energy diet (so foods that are more packed with energy like meats and starchy roots & tubers).
It looks like climate fluctuated between moist and dry periods, which required flexibility in diet (omnivory).. Increased meat consumption has been suggested as an important buffer against such environmental change (and helped expend into new unfamiliar environments), but high starch plant foods might have also been a very common and important part of the diet- especially when cooked. The timing of widespread cooking is not known, but it is argued that it was long enough ago to allow for biological adaptations to take place.
Note: Secure evidence of the use of fire to cook dates to about 400,000 years ago, though some suggestive evidence for a relationship between humans and fire dates to at least 1.6 mln years ago.
The fact that early hominins ate starchy foods is supported by various evidence (the paper goes through rather wordy technical anthropological examples that I fail to summarize in a simpler way). But while meat-eating evidence usually survives (e.g. animal remains with cut marks suggesting being butchered), evidence for plant foods doesn’t, which makes it hard to reconstruct ancestral diets based on physical remains alone (and biases them towards exaggerating meat eating).
Co-evolution of cooking & carb-digesting genes
Humans have the ability to digest starches with the help of enzymes in saliva- salivary amylase! AND humans are quite unusual as we have high levels of these enzymes, suggesting an adaptation to diets rich in cooked carbohydrates. Also, people from populations with high-starch diets have generally more AMY1 copies than those that have traditionally low-starch diets (hey! adaptation!).
Amylase (salivary amylase or AMY1)- enzyme that begins digesting starches in the mouth as it’s present in the saliva. Authors hypothesize that cooking and variation in the salivary amylase gene copy number are correlated.
The variation in copy numbers of salivary amylase genes is an important point of the paper – these enzymes are pretty much ineffective on raw starch, but cooking substantially increases their potential to provide energy/calories. So multiplication of the salivary amylase (AMY1) would become selectively advantageousonly when cooking became widespread. (It’s been estimated that the three human AMY1 genes have been evolving separately for less than 1 million years). The authors theorize a gene-culture co-adaptation scenario here: cooking starch-rich plant foods (cultural evolution) coevolved with increased salivary amylase activity in the human lineage (gene evolution). Without cooking, eating starch-rich plant foods probably couldn’t meet the high demands for preformed glucose noted in modern humans.
Note: A mutation that is selectively advantageous means a change in DNA that gives a survival advantage to a particular genotype under certain environmental conditions. SO in an environment where starches are available (e.g. you can find a lot of roots and tubers) and humans have learned to cook, having more copies of the AMY1 gene that aids in digesting cooked starch would allow those folks to survive more (e.g. in times of food crisis when they can’t hunt or gather other sources of food, etc.) vs. folks who don’t have that mutation.
To further test the paper’s hypothesis, we need “a convergence of information from archeology, genetics, and human physiology”. So let’s stay tuned 🙂
Well, i’m at around 900 words, which is more than the summaries i hope to do in the future! In my defense, this paper was FULL of fantastic information, often rather technical and challenging to explain in less words. I do have some extra content below i found fascinating if you found this summary interesting!
One fascinating topic is why we humans are susceptible to disease. If natural selection*** shapes successful traits, then why do we catch and develop so many diseases??
Evolutionary medicine is the field that tries to figure out why natural selection has left us so susceptible to illness (physical and mental). Here are some ways to explain our vulnerability to getting sick:
Reproduction vs. Health
I feel it is a common misconception that evolution wants us to live longer healthier lives (e.g. when people say that we’ve evolved to eat a certain way that allows us to live long and be disease-free).. and it is disturbing and heartbreaking for some to find out that evolution pretty much doesn’t care about your happiness, health, or longevity. 😦 Natural selection does not shape organisms to increase all those things, it shapes them to improve our fitness (Fitness NOT meaning long healthy lives [and with a six pack, preferably], but having more healthy children). So a trait that actually harms health will still get inherited if it increases reproduction!
One example I have heard of is having attractive female proportions (waist to hip ratio and all): it increases the chances that you will have more children by making a female desirable by men, but it is associated with higher risk of some diseases in old age.Another interesting example is higher mortality of males in adulthood- natural selection can favor such traits as risk taking, (which is important in attracting females as males compete for female attention), though it can decrease the lifespan of people whose personalities allow for increased risk taking.
I’ve seen that some paleo diet followers discuss evolution as a benevolent force that has figured out a way for humans to live long and prosper, and while that’s not true on the level of the individual (it technically “cares” that the species prospers by spreading), it doesn’t mean that you can’t use evolutionary theory to personally get healthier.
Our genes don’t match the environment!
Humans have created quite amazing conditions for ourselves- sanitation, roads, safe desktop jobs, public transit, etc. Things that make life comfortable and pleasant. And technologically advanced societies see higher rates of various disorders- autoimmune disease, obesity, drug abuse and so on. Many versions of certain genes are only problematic in modern environments. Proponents of all sorts of paleo-related diets, for example, claim our evolved preference for sugar and salt is dangerous in the world where processed foods are cheap and omnipresent (though adaptive in the wild as sugary ripe fruit are nutrient & calorie-rich). Another example is nearsightedness– it’s a problem in societies where kids begin reading early and is not a problem in populations that hunt & gather.
Other explanations are:
Pathogens simply evolve faster than their hosts (ourselves) so we will never have an immune system that is not vulnerable to some disease.
There are also tradeoffs: a certain trait can have great benefit in one way, yet it may have negative effect in other respects (again- being a seductive mess on a motorcycle might make females go crazy over you & want to reproduce, but it also makes one susceptible to dying from unsafe choices).
Once again, here is a GREAT read on EVOLUTION AND THE ORIGINS OF DISEASEby Dr. Nesse (MY INSTRUCTOR!) and Dr. Williams with MUCH more comprehensive explanations AND more interesting examples than I have in this blog entry. 😉
Evolution: change in genetic makeup of a population over generations; it requires genetic variation. The variation in genes arises from mutations and recombination.
Natural selection favors traits that allow an organism to produce more offspring [that is healthy enough to produce its own]
Fitness does not mean personal health & longevity. Fitness means how good you are at leaving a successful offspring.
Inclusive Fitness: unlike previously thought, evolution doesn’t work on the level of groups/species but on the level of individuals (so traits that aren’t “good” for the whole species but are good for this individual having more kids are going to be selected for). E.g. genes that make one aggressive to others will still pass on if it leads to this individual reproducing successfully.
HOWEVER, nice helpful personality traits are successful & are passed on (humans are incredibly altruistic vs. other animals) as it makes one do nice things for close relatives. Since you share genetic material (50% with each parent and siblings, 25% with cousins), the individual’s reproductive success actually includes not only how many healthy kids you produce, but how many your closest relatives do also!
There are no traits/genes that are awesome universally. The benefit of a certain trait is always in the context of the environment. E.g. sodium retention is prevalent in people that evolved around the equator since it gave them a selective advantage (salt is necessary to your body but is lost via sweat and urine.. you’d sweat way more in the hot climates).
[***Natural selection: imagine a group of people/dolphins/bugs. If this group’s members differ in some way that influences the likelihood that they’ll be part of the group in the future, this group will end up changing with time. So if some members have a genetic variation that influences how many kids they’ll have, in time this group will change and have more of the genetic trait that resulted in more kids!
A popular example is trees that once had light barks but got covered in black soot. The group of moths that used to hang out by the tree had variation in color- some white, some black.. The white ones will end up being eaten up by birds simply because they are now super visible on the dark bark and, in time, majority of moths will be black (the group has changed!) . Thus, a genetic trait is only “successful” in a context of an environment. There is nothing beneficial to being a black moth other than you’re less visible on black bark and thus will end up having more offspring than the white moths in the group.]