behavioral biology
gregladen | February 24, 2009
Why did the evolution of a large brain happen only once (among mammals, and in particular, primates?)
Larger brains have evolved a number of times. It seems that there has been a trend over several tens of millions of years of evolution of larger brains in various clades, such as carnivores and primates. There is probably a kind of arms race going on among various species in which a larger brain is an asset.
However, as you imply, a really large brain (like the extraordinarily large human brain) seems to be very rare. One of the reasons for this is that there are at least two major kinds…
gregladen | February 23, 2009My student, Marta, exploded the other day.
She was sitting there in class two weeks ago and exploded. She does not know that I know this, but I noticed it happen. Since she was sitting, as usual, in the front row, and it was all in her face, the other students did not see it but I definitely did.
By "exploding" in this case I mean that her brain suddenly filled with unanswered questions, which she then started sending me in frantic emails. Many of these questions are about things we will eventually get to in class, but some are on issues that we won't touch on at all. I decided, and I…
gregladen | February 12, 2009Or not.
Much is made of the early use of stone tools by human ancestors. Darwin saw the freeing of the hands ad co-evolving with the use of the hands to make and use tools which co-evolved with the big brain. And that would make the initial appearance of stone tools in the archaeological record a great and momentous thing. However, things did not work out that way.
It turns out that up-rightedness (bipedalism), which would free the hands, evolved in our ancestors a very long time (millions of years) prior to our first record of stone tools. The earliest upright hominids that are…
gregladen | December 31, 2008Naturalism is a potential source of guidance for our behavior, morals, ethics, and other more mundane decisions such as how to build an airplane and what to eat for breakfast.1 When it comes to airplanes, you'd better be a servant to the rules of nature or the airplane will go splat. When it comes to breakfast, it has been shown that knowing about our evolutionary history can be a more efficacious guide to good nutrition than the research employed by the FDA, but you can live without this approach. Naturalism works when it comes to behavior too, but there are consequences. You probably…
gregladen | December 23, 2008It has long been known that incest is not as bad as you think. Anti-cousin marriage laws are like prohibition laws and blue laws. They arise from a Christian conservative movement that swept Western Civilization from the late 18th century through the 19th century, up to about the time of the repeal of Prohibition.
Sure, marrying, or just plain having sex with, your sibling is disgusting. I mean, think about it. No, wait, don't even think about it. But cousin marriage? That depends. Your cousin may be kinda cute, you never know.
But seriously, anthropologists have long known of ... and…
gregladen | December 23, 2008This is from a news report of a paper I've not yet seen:
More than two-thirds of volunteers in the research study had to be stopped from administering 150 volt shocks of electricity, despite hearing a person's cries of pain, professor Jerry M. Burger concluded in a study published in the January issue of the journal American Psychologist.
"In a dramatic way, it illustrates that under certain circumstances people will act in very surprising and disturbing ways," said Burger.
The study, using paid volunteers from the southern San Francisco Bay area, is similar to the famous 1974 "obedience…
gregladen | December 6, 2008Individual animals that live and and forage in groups may not always benefit from a particular move (to or from a foraging site) in the same way as other individuals in the group. Therefore, there must be some kind of negotiation among the critters. Theoretical work almost always seem to show that consensus based group decisions will prevail because this minimizes individual costs. The altnernative, despotic decision (where a dominant individual decides where the group goes) should rarely happen. But the theory is apparently weak because despotic decision making seems to occur in nature.…
gregladen | October 27, 2008Go to any bar and you'll see a lot of males standing and sitting around not mating. I'll bet you would have guessed that the reason they are not mating is that no females will mate with them for one reason or another. But there is the distinct possibility that they are very inconspicuously resisting mating opportunities. It turns out that males can do this .... avoid mating without conspicuous resistance ... more easily than females. For obvious reasons.
This could be why what has become (inappropriately) known as "reversed sexual aggression" often goes unnoticed, and a recent study of the…
gregladen | October 17, 2008The Trivers Willard Hypothesis predicts that under certain conditions, individuals will bias their investment in offspring differently depending on the sex of the offspring. It is believed that this can be as extreme as infanticide or as subtle as providing different amounts of breast milk.
A new study by Katherine Hinde finds that macaques may do this. However, I think this may be counterintuitive.
Hinde uses data from 106 rhesus macaques (Macaca mulatta) to show that first time mothers produce richer milk when they have sons compared to when they have daughters. She suggests that "[t]…
gregladen | October 13, 2008 A very good day of grunting worms. Credit: Ken Catania So-called Gene-Culture Co-Evolution can be very obvious and direct or it can be very subtle and complex. In almost all cases, the details defy the usual presumptions people make about the utility of culture, the nature of human-managed knowledge, race, and technology. I would like to examine two cases of gene-culture interaction: One of the earliest post-Darwinian Synthesis examples addressing malaria and sickle-cell disease, and the most recently published example, the worm-grunters of Florida, which it turns out is best explained…
gregladen | September 29, 2008Human societies tend to be at least a little polygynous. This finding, recently reported in PLoS genetics, does not surprise us but is nonetheless important. This important in two ways: 1) This study uncovers numerical details of human genetic variation that are necessary to understand change across populations and over time; and 2) the variation across populations are interesting and, in fact, seem to conform to expectations (in a "we don't' really care about statistical significance" sort of way, for now) regarding human social organization.
Before examining the paper, we should…
gregladen | August 20, 2008A typical adult human recognizes that the image one sees in a mirror is oneself. We do not know how much training a mirror-naive adult requires to do this, but we think very little.
When a typical adult macaque (a species of monkey) looks in the mirror, it sees another monkey. Typical adult male macaques stuck in a cage with a mirror will treat the image as a fellow adult male macaque until you take the mirror out of the cage.
(Experiments that attempt to determine if an individual can recognize themselves in the mirror ultimately derive from what is known as the Gallup Test, after Gordon…
gregladen | August 17, 2008Why do we crave love so much, even to the point that we would die for it? To learn more about our very real, very physical need for romantic love, Helen Fisher and her research team took MRIs of people in love -- and people who had just been dumped.
Anthropologist Helen Fisher studies gender differences and the evolution of human emotions. She's best known as an expert on romantic love, and her beautifully penned books -- including Anatomy of.. ...
gregladen | July 23, 2008The phrase "genomic imprinting" has come to refer the turning off of a gene (a particular instance of a gene on a particular chromosome duplicated across the cells in a body) so that the gene is not expressed at all, with the turning off of the gene not caused in the body in question, but rather, during the previous generation by a process happening in the soma of one of the parents. A maternally imprinted gene is passed on to junior, but will not be expressed in junior. a paternally imprinted gene is passed on to junior, but will not be expressed in junior. Typically (as far as we know) a…
gregladen | June 30, 2008A study just out in PLoS Medicine suggests that an increasing trend of delaying childbirth is associated wiht a rising rate of the use of cesarean delivery. The explanation appears to be impared uterine function.
From the editor's summary:
Though it was not studied here, the researchers hypothesize that impaired uterine contractility may be a consequence of prolonged stimulation of the uterus by estrogen and progesterone, resulting from a prolonged interval between menarche and first birth. Further research is needed to understand the determinants and management of dysfunctional labor in…
gregladen | June 28, 2008There is new information from an older idea (from about 2000) by Paul Sherman and colleagues. The idea underlying this research is simple: Symptoms of illnesses may be adaptive. Indeed, this may be true to the extent that we should not call certain things illnesses. Like "morning sickness."
Broadly speaking, there are two different kinds of reasons that a woman may experience nausea in association with pregnancy. 1) This pregnancy thing is a complicated mess with all kinds of hormonal (and other) things going on, so you puke; or 2) a woman who is pregnant feels nauseous for good…
gregladen | June 24, 2008Sometimes boys are worth more, sometimes girls are worth more. In an evolutionary sense. Or, more correctly, the value of a certain sex ... as an offspring ... can be measured in fitness terms. Fisher noted this and hypothesized this was the explanation for the 50-50 sex ratio we usually see. As one sex becomes more rare, it becomes more valuable, and thus parents (mothers, perhaps, usually) bias towards that sex. Then the disparity goes away and thus the differential value goes away.
Of course, the truth is that we don't actually see the 50-50 sex ratio all the time ... many species…
gregladen | May 17, 2008MIT researchers found that phalaropes depend on a surface interaction known as contact angle hysteresis to propel drops of water containing prey upward to their throats. Photo by Robert Lewis The Phalarope starts out as an interesting bird because of its "reversed" sex-role mating behavior. For at least some species of Phalarope, females dominate males, forcing them to build nests and to care for the eggs that the females place there after mating. If a female suspects that a male is caring for eggs of another female, she may destroy the eggs and force the male to copulate with her a few…
gregladen | April 9, 2008Recently published research shows that individual humans will be nicer (more altruistic) when there is the possibility that the recipient of an act can respond verbally. The paper, "Anticipated verbal feedback induces altruistic behavior" is published in Evolution and Human Behavior for March.
These results are not particularly surprising, but it is important to confirm these things through experimental work. From the abstract:
[Humans may be...] motivated by concerns for praise and blame. ... we experimentally investigate the impact of anticipated verbal feedback on altruistic behavior…