“Nothing in biology makes sense except in the light of evolution.”
Dobhzhansky puts it so eloquently. Indeed, medicine, being founded in biology, can advance in great lengths if approached through the lens of evolution. Evolutionary biology elucidates how pathogenic virulence evolves, explains the relationship between pathogens and hosts, and answers questions as to why the human body is engineered in a certain way (flawed) that makes it vulnerable to diseases and disorders.
Discomforting conditions such as cough, pain, nausea and vomiting, and even reduced iron levels are adaptations that enable our bodies to fight off pathogens and are protective responses against infection. Chronic conditions such as diabetes can be explained as resulting from an evolutionary mismatch between our current diet and our early ancestors' needs. Our immune system provides ample opportunities for pathogens to evolve counter-defenses. Lastly, even behavioral choices such as safe sex or improved sanitation can alter a pathogen’s virulence. Such considerations are very important in the practice of medicine and even in public health policy because they inform us about better ways to approach disease and illness and tackle prevailing public health concerns. For example, If doctors and health care professionals understand the evolutionary theory behind virulence, they would best serve by advocating prevention as opposed to emphasizing treatment. Safe sex and using clean needles slow HIV transmission rates, and thus perpetuate low virulence and allow for the long term survival of hosts, saving more individuals from HIV infection.
Tuesday, December 1, 2009
Sunday, November 22, 2009
Ardi
How did bipedalism evolve?
Dr.Raichlen and colleagues asserted that, from their studies on walking energetics and biomechanics among adult chimpanzees and humans, bipedalism reduced the energy cost of walking compared to our ape-like ancestors. Bipedal walking is 75% less costly than qaudrupedal knucklewalking.
Furthermore, Dr. Lovejoy, in the article Reexamining Human Origins in Light of Ardipithecus Ramidus, explains how bipedalism permits many advantages in the lifestyle and survival of early hominids. It allowed for the transport of food across long distances, permitted the use of tools, facilitated female sexual selection on mates in exchange for valuable food, and might have played a pivotal role in male parental investment.
What forces led to the evolution of larger brain size in our early primate ancestors?
Certainly, bipedalism played a crucial role. Free hands allowed for multitasking and thus improved neural connections and signaling in the brain. Moreover, ovulatory crypsis and other reproductive characters(proliferation of sex-related traits for mate selection etc.) have often been believed to intensify social behaviors and also allowed the rapid development of the "unusually enegry-thirsty brain." Conversely, the invention/acquisition of fire, or any other simple physical capacity does not solely explain the enlargment of the brain because they are believed to have proceeded or occurred in relation to such unique reproductive and behavioral strategies.
Dr.Raichlen and colleagues asserted that, from their studies on walking energetics and biomechanics among adult chimpanzees and humans, bipedalism reduced the energy cost of walking compared to our ape-like ancestors. Bipedal walking is 75% less costly than qaudrupedal knucklewalking.
Furthermore, Dr. Lovejoy, in the article Reexamining Human Origins in Light of Ardipithecus Ramidus, explains how bipedalism permits many advantages in the lifestyle and survival of early hominids. It allowed for the transport of food across long distances, permitted the use of tools, facilitated female sexual selection on mates in exchange for valuable food, and might have played a pivotal role in male parental investment.
What forces led to the evolution of larger brain size in our early primate ancestors?
Certainly, bipedalism played a crucial role. Free hands allowed for multitasking and thus improved neural connections and signaling in the brain. Moreover, ovulatory crypsis and other reproductive characters(proliferation of sex-related traits for mate selection etc.) have often been believed to intensify social behaviors and also allowed the rapid development of the "unusually enegry-thirsty brain." Conversely, the invention/acquisition of fire, or any other simple physical capacity does not solely explain the enlargment of the brain because they are believed to have proceeded or occurred in relation to such unique reproductive and behavioral strategies.
Sunday, November 15, 2009
Genesis
In Conceit of Hindsight, Dawkins warns us against a pair of temptations. First, he briefly mentioned that we should not always seek for patterns when looking at evolutionary history, as if it aims to arrive at a certain destination or abide with certain rules. Albeit the fact that there are indeed some unifying theories, these concepts vary and we should still be cautious not to shrink it as such. Second, we should avoid seeing the past through the lens of our own existence. The laws of physics do not necessarily suggest that the universe was created so that we house in it; in fact Smolin theorized that our universe may have been a product of a random “mutation.” Also, all the different organisms throughout evolutionary history did not exist just to foreshadow us. We should avoid thinking that all species are “progressing” towards one main line of evolution, towards humans or any other modern species.
In Eve’s Tale, the Y-chromosome and mitochondrial DNA make tracing our ancestors easy. The non-recombining portion of the Y-chromosome always passes through the main line while the mitochondria exclusively passes along the female line, and thus these allow for studying a male or female line of ancestry plausible. However, these methods are limiting, because we could still trace ancestry lines without being confined to strict gender lines. Reliance on a single gene can be misleading. There are genes outside the Y-chromosome and the mitochondria that can still be passed from generation to generation.
Templeton was able to date back human migrations out of Africa through analyzing 13 haplotypes ( a long-lived recognizable chunk of DNA), coupled with fossil calibrations. He was able make inferences of our genetic history over the past 2M years and he found out that there were 3 major migrations out of the continent.
In Eve’s Tale, the Y-chromosome and mitochondrial DNA make tracing our ancestors easy. The non-recombining portion of the Y-chromosome always passes through the main line while the mitochondria exclusively passes along the female line, and thus these allow for studying a male or female line of ancestry plausible. However, these methods are limiting, because we could still trace ancestry lines without being confined to strict gender lines. Reliance on a single gene can be misleading. There are genes outside the Y-chromosome and the mitochondria that can still be passed from generation to generation.
Templeton was able to date back human migrations out of Africa through analyzing 13 haplotypes ( a long-lived recognizable chunk of DNA), coupled with fossil calibrations. He was able make inferences of our genetic history over the past 2M years and he found out that there were 3 major migrations out of the continent.
Tuesday, October 27, 2009
New Moon
Dawkins remarks that it is possible for mutual altruism to incur, and thereby solve the Prisoner’s Dilemma, if conditions such as iterated encounters, threat of retaliation, and “forgiveness” are met. He uses the example of the live-let-live strategy employed by British and German troops on WW1 and the strict alternation of sexes by hermaphrodite fishes. Such dynamics is also echoed in a special kind of mutual altruism among vampire bats.
The work of G.S. Wilkinson explains how non-kin individuals engage in altruistic behaviors. Albeit a significant amount of blood-sharing cases involve close relatives, he found that vampire bats sometimes donate blood to their unrelated counterparts to save them from starving. Such behavior is within the tenets of a Prisoner’s Dilemma. A Donate-Donate strategy is a win-win strategy because the cost of donating trumps the huge benefit of saving a comrade's life; in addition, when the unfortunate time comes of an unlucky forage, a vampire bat would greatly benefit from the prospect of a reciprocal donation. Interestingly, this is evidenced by repeating experiments from Wilkinson wherein a bat was removed and starved for a night and returned to the roost. In thirteen cases, twelve involved donation from a previous benefactor/friend, proving the condition for reciprocation.
The work of G.S. Wilkinson explains how non-kin individuals engage in altruistic behaviors. Albeit a significant amount of blood-sharing cases involve close relatives, he found that vampire bats sometimes donate blood to their unrelated counterparts to save them from starving. Such behavior is within the tenets of a Prisoner’s Dilemma. A Donate-Donate strategy is a win-win strategy because the cost of donating trumps the huge benefit of saving a comrade's life; in addition, when the unfortunate time comes of an unlucky forage, a vampire bat would greatly benefit from the prospect of a reciprocal donation. Interestingly, this is evidenced by repeating experiments from Wilkinson wherein a bat was removed and starved for a night and returned to the roost. In thirteen cases, twelve involved donation from a previous benefactor/friend, proving the condition for reciprocation.
Friday, October 23, 2009
Mothers and Daughters
The conflict boils down to whose preference of sex ratio will be maintained--- the Queen’s 1:1 or the female workers’ 3:1 female to male ratio.
Why does the Queen invest in a 1:1 sex ratio?
Her genes can benefit best if she invests equally in both sexes. This is supported by Fischer calculations on optimal sex ratios done by Trivers and Hare.
Why do female workers favor a 3:1 ratio, or more sisters?
Since sisters share the same father, they share his genes 100% of the time. On the other hand, males, which are unfertilized eggs and do not require a father, only carry the queen’s genes. Thus, sisters are more related to one another than to their brothers, whose genes they share only 25% of the time. It is best for a female worker to refrain from rearing and let the queen be a sister-making machine.
Who wins?
Using 20 species of ants, Triver and Hare estimated sex ratios in terms of investment in reproductives and found a 3:1 female to male ratio. “Workers are running the show for their own benefit.”
What are the exceptions?
Some species of ants use slaves (workers from other colonies) to perform the chores. Long story short, the power now lies on the slaves, which are unrelated to the rest of the brood, rather than on the true-born workers. The queen can thus get away with the slaves countermeasures because their countermeasures won’t work on her, being totally unrelated to them.
In some species, a queen mates with several males, which makes the average relatedness of sisters to be as low as 25%.
My head is spinning.....
Why does the Queen invest in a 1:1 sex ratio?
Her genes can benefit best if she invests equally in both sexes. This is supported by Fischer calculations on optimal sex ratios done by Trivers and Hare.
Why do female workers favor a 3:1 ratio, or more sisters?
Since sisters share the same father, they share his genes 100% of the time. On the other hand, males, which are unfertilized eggs and do not require a father, only carry the queen’s genes. Thus, sisters are more related to one another than to their brothers, whose genes they share only 25% of the time. It is best for a female worker to refrain from rearing and let the queen be a sister-making machine.
Who wins?
Using 20 species of ants, Triver and Hare estimated sex ratios in terms of investment in reproductives and found a 3:1 female to male ratio. “Workers are running the show for their own benefit.”
What are the exceptions?
Some species of ants use slaves (workers from other colonies) to perform the chores. Long story short, the power now lies on the slaves, which are unrelated to the rest of the brood, rather than on the true-born workers. The queen can thus get away with the slaves countermeasures because their countermeasures won’t work on her, being totally unrelated to them.
In some species, a queen mates with several males, which makes the average relatedness of sisters to be as low as 25%.
My head is spinning.....
Monday, October 12, 2009
Natural Selection and Sexual Selection
Darwin personifies nature as “an active power” that affords better chances of occurrences for profitable variations. Changes in the conditions of life yield individuals with a wide array of variability. In this connection, the slightest differences in structure can turn the scale for the struggle of existence; individuals carrying desirable traits will survive and reproduce more. Thus, natural selection is a tool for “scrutinizing the traits”, rejecting the bad ones and preserving the good ones for subsequent generations. As one example, he states how natural selection “gives” grouse their particular color for preserving them from prey hawks, who are guided by eyesight. On a different note, he distinguishes this from sexual selection, which he calls something that depends not on the struggle for existence but on the struggle between individuals of one sex for the possession of the other sex. E.g., the male Guiana birds display their plumage to females whose primary criteria for the fittest mate is attractiveness.
Dawkins, on the other hand, is saying the same thing but blurs the line between the two. He asserts that natural selection operates in conjunction with sexual selection so as to enable “selfish machines” have as many surviving offspring as possible. The challenge comes when the asymmetry arises between the sexes as to who will invest more in producing the offspring, and that’s when sexual selection comes in handy. Females start off with the disadvantage of investing more in the form of a large egg and stands to lose more if the offspring dies than the male who can at anytime abandon without any cost; hence there must be some sort of evolutionary counter pressure against males. An example is the domestic-bliss strategy wherein females choose their males carefully, looking for fidelity and domesticity traits.
Dawkins, on the other hand, is saying the same thing but blurs the line between the two. He asserts that natural selection operates in conjunction with sexual selection so as to enable “selfish machines” have as many surviving offspring as possible. The challenge comes when the asymmetry arises between the sexes as to who will invest more in producing the offspring, and that’s when sexual selection comes in handy. Females start off with the disadvantage of investing more in the form of a large egg and stands to lose more if the offspring dies than the male who can at anytime abandon without any cost; hence there must be some sort of evolutionary counter pressure against males. An example is the domestic-bliss strategy wherein females choose their males carefully, looking for fidelity and domesticity traits.
Tuesday, September 29, 2009
Battle of the Sexes
According to Dawkins, an evolutionary stable strategy (ESS) is a strategy that the majority of the population employs. In a population of individuals maximizing their own successes, the only strategy that persists will be the one that cannot be bettered by any deviant individual. An example of an ESS is Fisher’s sex ratio of 50:50 males to females. If a population suddenly began to shift its preference on one sex over the other, in succeeding generations, that sex will on average have lower mating successes, and thus, offspring-production is reduced. In time, selection will favor genes that biases towards the opposite sex, until the 50:50 ratio is reached. The strategy of a 50:50 sex ratio is an ESS in the sense that any deviation from it leads to a net loss (Dawkins, 145).
Autosomal chromosomes, being equal in number and having homologs in both males and females, will likely favor the 50:50 sex ratio. Sex chromosomes will be biased towards one sex over the other since the sexes differ on a single chromosome- the Y chromosome. It is probable that the X chromosome can select repressors on the Y-chromosome, and thus favor the production of females (Werren, 1998). Cytoplasmic elements, usually obtained from the female, can also distort the 50:50 sex ratio. Indeed , the majority of sex distorters are cytoplasmic and they favor the sex through which they will be transmitted (Hardy, 2002).
Image: www.sciencedaily.com
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