116

This is a interesting question and for a long time it was thought that they do not age. In the meantime there are some new papers which say that bacteria do indeed age. Aging can be defined as the accumulation of non-genetic damages (for example oxidative damage to proteins) over time. If too much of these damages are accumulated, the cell will eventually ...


72

Why do we age is a classical question in Evolutionary Biology. There are several things to consider when we think of how genes that cause disease, aging, and death to evolve. One explanation for the evolution of aging is the mutation accumulation (MA) hypothesis. This hypothesis by P. Medawar states that mutations causing late life deleterious (damaging) ...


68

Crystallin proteins are found in the eye lens (where their main job is probably to define the refractive index of the medium); they are commonly considered to be non-regenerated. So, your crystallins are as old as you are! Because of this absence of regeneration, the accumulate damage over time, including proteolysis, cross-linkings etc., which is one of ...


25

The 'wear and tear' argument is most likely true but it is also interesting to reason about ageing as inevitable from the evolutionary point of view. To set up the argument, we need two things: First, each individual has got a 'reproductive potential' which is realised throughout life. This means a deleterious mutation which has an effect in early life, ...


22

I've been doing some reading, and have come up with the following interesting information. Telomeres During cell division the DNA is replicated, but the mechanism is imperfect and in each round of cell division a small section is lost from the end of each chromosome. To compensate and protect the genetic information there are caps – regions of excess ...


22

This is a very good question. There is a big ongoing field of research called "evolution of aging/senescence" that tackles this question. I won't give you a complete overview of the different hypothesis the could explain why we age but here is a fundamental concept that is to know. We'll assume that there is some extrinsic mortality, mortality against ...


22

I like Mowgli's answer, because it is a non-obvious example. However I would also point out that there are many, many protein-based structural components in the body that we know do not regenerate due to associated pathologies; so presumably these structural proteins are as old as from when they first arose in developemnt. Take the stereocilia on hair cells ...


20

The immortal jellyfish can revert back to its immature polyp stage after reaching maturity, then mature again, over and over. You can read more on the wikipedia page, but this ability means it can potentially avoid senescence altogether.


18

From a certain point of view you could argue that our bodies have an inherently limited lifespan; Telomeres are extensions to the end of chromosomes that prevent damage or loss of genetic information during cell division. Telomeres are not replaced (in normal cells), which gives rise to a replicative lifespan; the number of times a cell can divide before ...


17

Each individuals hair colour is determined by the particular pigment they produce (called melanin - the same stuff in your skin that makes you tan). As the body ages this pigment (produced by the melanonocytes - cells that reside in the hair follicle) is produced less and less, until the hair is no longer coloured, and appears grey. This is unique to each ...


17

The answer(s) to this question can fill libraries. But I can give a few pointers here, as the question is relevant and timely, giving the tendency to an ever increasing life expectancy of the general populace in developed countries (notable exception: US). I think your question can broadly be answered by the fact that degenerative processes in the brain ...


16

Hydra are just one of the many organisms which are immortal. That is to say all their cells divide forever - there is no senescence (planned cell death) in any of their cells. Interestingly Hydrae that reproduce sexually age and die, but asexual reproduction appear to be immortal. Animals that are immortal more often reproduce asexually... this may only be ...


15

Well, this needs to be broken down into two parts. Do Crocodilians age (undergo senescence), and are Crocodilians immortal (will only die of external causes)? Are Crocodilians immortal? - No. They appear to live about as long as humans before they die. Measuring crocodile age is unreliable, although several techniques are used to derive a reasonable ...


15

I now found this Wikipedia article on biological immortality. It's pretty much what I was looking for. Wikipedia describes the phenomenon as follows: Biological immortality refers to a stable or decreasing rate of mortality from cellular senescence as a function of chronological age. Various unicellular and multicellular species may achieve this ...


15

The HeLa cell line is undoubtedly the most used and investigated human immortal tumor cell line. Extracted from a cervical tumor from Henrietta Lacks in 1951 at Johns Hopkins hospital, Baltimore, MD these cells proved immortal and are still used in many, many labs worldwide today. It is the oldest human cell line in use and, therefore, the oldest human ...


14

Because evolution isn't about individuals: it's about species. What matters to natural selection isn't how long you live, but how many grandchildren you have. A long lifespan can be an evolutionary advantage, but like any trait, it's only an advantage to the extent that allows you to reproduce more. It would seem that a longer lifespan would be advantageous ...


13

Yes. The Bristlecone Pine, Pinus longaeva, is one example. This species boasts the oldest individual living organisms, and also has been convincingly argued by Lanner and Connor (2001) to show no evidence of senescence. While the Wikipedia page on Biological Immortality (as of June 2013) unfortunately ignores plants, the pages on Negligible Senescence and ...


13

Actually, genetically, there is no reason for animals to continue to exist after they have procreated. If you look at salmon, they die immediately after procreating, which is probably the most efficient way to carry the best genes to the next generation. In the case of mammals, they need to teach their offspring where to find food, where to find water and ...


12

It's worth noting that earlier this month a large body of resveratrol research was retracted: The University of Connecticut, in what clearly seems like an attempt to get ahead of damaging news, has announced an “extensive” investigation into research misconduct involving one of its scientists, Dipak K. Das. According to a press release, the ...


12

Short answer Large animals do get cancer. They may contract cancer with an incidence less than that estimated by absolute cell numbers, but there seems to be a lack of data on cancer rates in large animals to support this hypothesis conclusively. Background Whales contract cancer (Martineau et al, 2002). There does, however, seem to be a lack of correlation ...


11

This isn't so precisely focused on tortoises, but a general theory in evolutionary biology for why some animals live longer is K vs r selection theory. The idea here is that animals will make a sort of evolutionary 'choice' and configure themselves to breed as numerously and quickly as they can. This is called 'r' selection, named after the constant that ...


10

Free radicals are damaging because their unpaired electrons (or not fully filled valence shell) makes them highly reactive species. They are often considered together with highly oxidizing "reactive oxygen species" (ROS) such as peroxides. They are especially problematic for cell membranes and DNA. In the latter they can react with (oxidize) heterocyclic ...


10

Caspase do not directly kill the cell, but rather activate a process known as apoptosis, or programmed cell death. The programmed part is there to distinguish it from other types of cell death, such as necrosis, which are more aspecific death processes. Coming back to caspases, they are a series of proteasis, that can activate in cascade in response to a ...


10

Well, Erickson et al (2011) attribute the increase in brain volume in the aerobic exercise group to brain-derived neurotrophic factor (BDNF). Specifically (p. 3020): In fact, we found here that changes in serum BDNF levels were associated with changes in anterior hippocampal volume; an important link because the hippocampus is rich in BDNF, and BDNF ...


10

I think it is the wrong question. You assume that eukaryotes developed from a single-cell organism with circular DNA. Then, clearly, there must have been an advantage of (newly) developing a linear genome. But eukaryotes could have developed from an organism with linear DNA, too. There are still a few bacterial species with linear chromosomes, so this is not ...


10

Gametes (sperm and ovum), which fuse to form a zygote, arise from germ cells (spermatogonia and oogonia). Germ cells, like stem cells, are maintained carefully i.e the genome is preserved and transposition/recombination events are tightly controlled via different mechanisms. So these germ cells don't have shortened telomeres. Also, during early embryonic ...


9

If you search clinicaltrials.gov (maintained by the NIH) for "resveratrol", you'll find 44 clinical trials, many of them ongoing or not yet started. A recent review by Smoliga JM et al states in the abstract: "Although the supporting research in laboratory models is quite substantial, only recently data has emerged to describe the effects of resveratrol ...


9

First of all, in eukaryotes (as far as I'm aware), older cells can be distinguished from younger cells due to telomere shortening, so there is an ageing process. HeLa cells mentioned by @Gary Chou have a more active telomerase which mitigates telomere shortening, allowing cells to continue to divide indefinitely. I think it's a very interesting question ...


9

Interesting question. My answer is no, but it requires a rather science-fiction style answer - at least it's beyond current technology, but here goes: My Assumptions I make the simplifying assumption that ageing is only related to telomere length. Thus by "avoid ageing" I assume you mean "avoid telomere shortening". Also to clarify things for others, I'll ...


9

A very interesting example are the cohesin molecules holding sister chromatids together in the oocytes (so only applicable to females, sorry!). Cohesion is established in utero, and these molecules are not recycled throughout life (AFAIK only shown directly for mice, not humans - https://www.ncbi.nlm.nih.gov/pubmed/20971813, https://www.ncbi.nlm.nih.gov/...


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