A Chain of Ancestors

One of the better examples I’ve yet found that conveys the concept of evolution comes from the 2002 NOVA documentary “Search for the First Human.” The main focus of the video is the species Orrorin tugenensis and it’s possible place in our family tree six million years ago. However, two particular segments stand out to me, and I think do a pretty good job of conveying the idea of evolution to students.

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Darwin, Oversimplified

ChuckDCharles Darwin recognized early on the potential for people to oversimplify his writing. In particular, he was adamant that not everything in evolution was the result of adaptation by natural selection, though he worried that others would caricature his work in that way. In other words, Darwin was not as Darwinian as he is sometimes portrayed. The following passage comes from the sixth edition of On the Origin of Species (1872: 421):

 

 

“I have now recapitulated the facts and considerations which have thoroughly convinced me that species have been modified, during a long course of descent. This has been effected chiefly through the natural selection of numerous successive, slight, favourable variations; aided in an important manner by the inherited effects of the use and disuse of parts; and in an unimportant manner, that is in relation to adaptive structures, whether past or present, by the direct action of external conditions, and by variations which seem to us in our ignorance to arise spontaneously. It appears that I formerly underrated the frequency and value of these latter forms of variation, as leading to permanent modifications of structure independently of natural selection. But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position—namely, at the close of the Introduction—the following words: “I am convinced that natural selection has been the main but not the exclusive means of modification.” This has been of no avail. Great is the power of steady misrepresentation; but the history of science shows that fortunately this power does not long endure.”

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Developmental Plasticity and the “Hard-Wired” Problem

“Development is the missing link between genotype and phenotype, a place too often occupied by metaphors in the past … But a strong emphasis on the genome means that environmental influence is systematically ignored. If you begin with DNA and view development as “hard-wired,” you overlook the flexible phenotype and the causes of its variation that are the mainsprings of adaptive evolution.” (Mary Jane West-Eberhard, 2003: 89-90)

“Genes, unlike gods, are conditional. They are exquisitely good at simple if-then logic: if in a certain environment, then develop in a certain way… So here is the first moral of the tale: Don’t be frightened of genes. They are not gods; they are cogs. (Matt Ridley, 2003: 250)

 

Plasticity: actor Christian Bale at two points in time. Same genes, different phenotypes.

Plasticity: actor Christian Bale at two points in time. Same genes, different phenotypes.

In his book The Triple Helix, Richard Lewontin told the story of the molecular biologist and Nobel laureate Sydney Brenner, who – while speaking at a conference – predicted that one day we would be able to “compute” an organism (2002). All we would need are two things: the organism’s full genome and powerful enough computers that were up to the task.

The idea is seductive. Genes are sometimes seen as self-sufficient molecules, almost existing in a vacuum, that contain all the information necessary to code for proteins. From there, it’s not a very big logical leap to think that if you had the genome, you could enter the code in some database, hit “run,” and then watch some digitized version of the organism unfold.

In fact, scientists are doing something much like this for the tiny roundworm C. elegans with the project OpenWorm. Yet even for a relatively simple organism such as this, with only about a thousand cells in total, there are reasons to be cautious. As The Economist warned in its write-up of OpenWorm: “Attempting to simulate everything faithfully would bring even a supercomputer to its knees.” However, this isn’t due solely to the limits of computing power (what if we had a super-duper computer!?). Rather, it’s a matter of how the question is framed.

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Our Essential, Fragile Bonds

Today would have been my brother’s birthday, and I’ve been saving this passage from Boris Pasternik’s Doctor Zhivago to mark it. Here the title character, Yura Zhivago, is speaking to Anna Ivanovna who feared she was terminally ill. He offers what he thinks happens to us when we die, and the primacy of our social connections:

“So what will happen to your consciousness? Your consciousness, yours, not anyone else’s. Well, what are you? There’s the point. Let’s try to find out. What is it about you that you have always known as yourself? What are you conscious of in yourself? Your kidneys? Your liver? Your blood vessels? No. However far back you go in your memory, it is always in some external, active manifestation of yourself that you come across your identity–in the work of your hands, in your family, in other people. And now listen carefully. You in others–this is your soul. This is what you are. This is what your consciousness has breathed and lived on and enjoyed throughout your life–your soul, your immortality, your life in others. And what now? You have always been in others and you will remain in others. And what does it matter to you if later on that is called your memory? This will be you–the you that enters the future and becomes part of it.” (Boris Pasternak, Doctor Zhivago, p. 68)

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I still haven’t mastered the ability to completely separate the academic and the personal, and I’m not sure I completely want to. Instead of an impenetrable wall between them, perhaps, for me, there is a wrought-iron fence with an open gate. What I mean is that I often go between the two, allowing them to inform each other. The passage from Zhivago is from literature, and is not a scientific statement. But it runs parallel to some aspects of science, which seems poetic to me, particularly on a day I’m thinking of my brother. 

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Did Pairbonds Evolve to Be Asymmetrical?

“I know you belong to somebody new, but tonight you belong to me.” Rose and David 

“I wanted love, I needed love. Most of all, most of all.” Auerbach and Carney (1)

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Several researchers have attempted to reconstruct the very difficult problem of why pairbonding may have evolved in humans (I wrote about this here, but a decent guess is that this began around 2 million years ago. Maybe). Those reconstructions often come with an addendum, which predict that pair-bonds would not be completely symmetrical. Instead, either males or females would have more of an incentive to initiate or maintain a long-term bond, and this would depend on the reasons that pairbonding evolved in the first place.

For example, here is David Buss, explaining why males are more likely to fall in love first:

“Because love is an emotion tethered to long-term mating; because fecundity and reproductive value is so critical to men in selecting a long-term mate; and because physical appearance provides an abundance of cues to a woman’s fecundity and reproductive value, we can predict that men will experience “love at first sight” more often than women. The empirical evidence supports this prediction.” (Buss, 2006: 69)

Australopithecus afarensis ("Lucy"), out with her date. Source.

Australopithecus afarensis (“Lucy”), out with her date around 3.6 mya. This portrayal of an early pairbond is speculative, but it ‘s probably not accurate. Source: AMNH.

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Human Evolution, an Ongoing Story

Over at Scientific American, Kate Wong compiled a list of some of the most compelling discoveries in human evolution from 2013. I won’t rehash her entire list here, but the ones that will stick with me for a while include the variation found among the Dmanisi hominins, probably all within the same species. The other is the genetic evidence for interbreeding between Neanderthals, Denisovans, and other extinct humans. Fascinating.

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Flexible Love, at Any Age

The New York Times runs a series of short videos titled “Modern Love” (does David Bowie know about this?). The latest installation is narrated by a 71 year-old woman who describes the experience of falling in love at her age, comparing it to her younger days. She talks about differences in preparing for dates, perceptions of the concept of ‘soulmates,’ the sense of urgency, jealousy, ephemerality of life and relationships, and the pain of loss. Pretty thorough for a 2 minute video.   

To me, the most interesting part is that love really can strike at any age, illustrating the gap between proximate and evolutionary levels. Evolutionary hypotheses for the origin of pair-bonding (and love) often highlight some function related to reproduction. Robin Dunbar  summarized four possibilities: 

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Part 13: Humans are (Blank)-ogamous: Is Monogamy ‘Natural?’

This is part of a series on the evolution of human mating behavior, comparing evidence for promiscuity and pair-bonding in our species. Please see the Introduction here.

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(Left) My paternal grandparents with my father as a toddler. (Right) Their 50th anniversary.

Left: My paternal grandparents with my father as a toddler. Right: their 50th wedding anniversary (it’s the best picture I could find).

Are humans naturally monogamous? Oprah Winfrey says ‘no.’That settles it, then. Maybe.

Oprah (she needs no last name) was a guest on a morning talk show, and the topic of discussion was two recent articles on the origins of monogamy in mammals (Lukas & Clutton-Brock, 2013) and another specifically on primates (Opie et al, 2013). Both articles are impressive for their large databases and attention to detail. The first looked at 2545 species of mammals while the Opie article examined 230 primate species.[1]

Both studies focused specifically on social, rather than sexual, monogamy. This distinction is important because sexual exclusivity was not what was being measured here. Rather, social monogamy was defined by both studies as simply living in breeding pairs. The Lukas & Clutton-Brock paper added that in social monogamy the pair shared a common territory, and “associate with each other for more than one breeding season” (p. 526).

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The Zen Master and the Infanticidal Primates

A recent paper has concluded that prevention of infanticide was the most likely precursor to monogamous mating systems in some primate species. Another paper suggested a different possibility in mammals more generally, namely that under certain ecological conditions females are so dispersed that the best strategy for a male is to remain close to a rare female when he finds her. This prevents other males from mating with her, and increases the chances of successfully passing on his genes. 

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Langur mother with dead infant. (From http://www.brown.edu/Research/Primate/LPN50-1.html)

I’m still sorting through what all this means, and wonder if the search for broad patterns oversimplifies things too much. As Peter Gray put it: “It’s all so confusing, if lead researchers can’t seem to find similar evolutionary grounds behind social monogamy.” Anyway, if prevention of infanticide really was the key to jump-starting monogamy (at least in some primate species), it makes me think of its downstream consequences. This reminds me of the parable of the Zen Master and the Little Boy.

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Check Your Ego

Neil de Grasse Tyson on the cosmic perspective:

“I assert that if you are depressed after being exposed to the cosmic perspective, you started your day with an unjustifiably large ego.”

Existence itself is awe-inspiring enough.

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