Tag Archives: biology

lobsters are not immortal, or at least only sort of

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From McGill University:

So why do we stop growing, while lobsters don’t? The cells that make up our body are constantly making new cells by dividing. A biological technicality causes us to lose a bit of DNA at the ends of our chromosomes (structures made up of DNA and proteins) after each replication. DNA contains the blueprint for our lives, so in order to make sure we aren’t losing crucial information during these divisions, the long molecules of DNA are protected by shorter segments of DNA at their ends called “telomeres.” An analogy would be the plastic tips on a shoelace that prevent it from unraveling. When a cell multiplies, the only part of the chromosome that is lost is a piece of the telomeres. But as we age, our telomeres get shorter, until they reach a critical point where the cell can no longer replicate without damage to its essential DNA. When this occurs, the cell becomes inactive or dies. Shortening of telomeres is linked to senescence and increased risk of disease. Other contributors to aging include oxidative stress (hence the appeal of antioxidants).

Lobsters have a perpetual supply of telomerase – the enzyme that can restore telomeres, helping cells avoid that fateful end. Humans also have telomerase, just not enough to overcome the constant shortening of telomeres. In fact, telomerase is often found in cancer cells, giving tumours a survival advantage.

Unfortunately for our pal Larry, a large supply of telomerase can be a double-edged sword. Lobsters are still more likely to die with age because their hard-shell exoskeleton moults and has to be regrown. This requires reams of energy, eventually too much. As a result, common causes of death for lobsters are exhaustion, immobility, and shell disease, although the leading cause is still predation.

McGill

The article goes on to say that there are actually some jellyfish that are biologically immortal, meaning they do not age or ever die of old age, although they can be killed.

Given an infinite span of time, the odds of a “biologically immortal” organism being killed would seem to be 100%. So this does not sound like immortality to me in a colloquial sense, But figure out this mystery and come up with a drug to restore our telomeres without causing cancer, and we could live for a long, long time if we are careful. Would our brains hold up more than a century or so?

Interestingly, and this is a frequent point of conversation my son likes to bring up, the Norse gods are “biologically immortal” because they do not age but they can be killed (sorry, Thor fans). But the Greek/Roman gods are truly indestructible. I recall one story where Zeus was cut up into little pieces and put into a bag by another one of the gods. Eventually, somebody let him out and the pieces just assembled themselves together again and he continued being Zeus.

Red Queens and Black Queens

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It sounds like a fantasy novel, but the Red Queen hypothesis is about species competing and co-evolving with one another over long periods of time. It is named after the Red Queen in Through the Looking Glass, who said “it takes all the running you can do, to keep in the same place.” In other words, species have to constantly evolve and adapt, or they go extinct. 

The Black Queen hypothesis is hard for me to understand, but it refers to

the queen of spades in the game Hearts, where the usual strategy is to avoid taking this card. Gene loss can provide a selective advantage by conserving an organism’s limiting resources, provided the gene’s function is dispensable. Many vital genetic functions are leaky, thereby unavoidably producing public goods that are available to the entire community. Such leaky functions are thus dispensable for individuals, provided they are not lost entirely from the community. The BQH predicts that the loss of a costly, leaky function is selectively favored at the individual level and will proceed until the production of public goods is just sufficient to support the equilibrium community; at that point, the benefit of any further loss would be offset by the cost. Evolution in accordance with the BQH thus generates “beneficiaries” of reduced genomic content that are dependent on leaky “helpers,” and it may explain the observed nonuniversality of prototrophy, stress resistance, and other cellular functions in the microbial world.

In other words, organisms can sort of help their rivals, and there can be some survival advantage to this over long periods of evolutionary time. I’m not sure I quite get it, but there it is.

on leadership…

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It seems to be out of fashion, but I always find it interesting when people try to draw social parallels between people and animals. This reminds me of E.O. Wilson’s Sociobiology, which spends hundreds of pages on ants and termites, and after I worked my way through it I actually feel more of an affinity for these creatures and the complex mini-civilizations they have built.

Leadership in Mammalian Societies: Emergence, Distribution, Power, and Payoff

Leadership is an active area of research in both the biological and social sciences. This review provides a transdisciplinary synthesis of biological and social-science views of leadership from an evolutionary perspective, and examines patterns of leadership in a set of small-scale human and non-human mammalian societies. We review empirical and theoretical work on leadership in four domains: movement, food acquisition, within-group conflict mediation, and between-group interactions. We categorize patterns of variation in leadership in five dimensions: distribution (across individuals), emergence (achieved versus inherited), power, relative payoff to leadership, and generality (across domains). We find that human leadership exhibits commonalities with and differences from the broader mammalian pattern, raising interesting theoretical and empirical issues.

 

Freeman Dyson on the origin of life

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Recently I remembered that Freeman Dyson has this dissenting view on the origin if life. It’s a little hard to follow, but the basic idea is that life preceded DNA/RNA. It started as simple molecules that were able to metabolize, grow and evolve, but not able to replicate themselves efficiently. In other words, life without DNA. If I understand it correctly, this means DNA/RNA would have had to arise separately, perhaps as a virus that then infected the larger molecules and gave rise to modern cells. The most interesting implication, to me, is that this means life arose more than once. So life arising is not as rare an event as we might think. Maybe it happens relatively frequently under a range of conditions, and maybe Earth is not the only place it happens. Maybe it arises frequently, but it rarely gets off the ground. Dyson admits his theory is rejected or ignored by most biologists, but he insists it fits the facts. I was reading this abstract in Trends in Ecology and Evolution, which was a little over my head but reminded me of Dyson’s theory.

Despite recent progress, the origin of the eukaryotic cell remains enigmatic. It is now known that the last eukaryotic common ancestor was complex and that endosymbiosis played a crucial role in eukaryogenesis at least via the acquisition of the alphaproteobacterial ancestor of mitochondria. However, the nature of the mitochondrial host is controversial, although the recent discovery of an archaeal lineage phylogenetically close to eukaryotes reinforces models proposing archaea-derived hosts. We argue that, in addition to improved phylogenomic analyses with more comprehensive taxon sampling to pinpoint the closest prokaryotic relatives of eukaryotes, determining plausible mechanisms and selective forces at the origin of key eukaryotic features, such as the nucleus or the bacterial-like eukaryotic membrane system, is essential to constrain existing models.