5

and there is not much evolutionary pressure to loose it The energetic cost of replicating antibiotic resistance genes in the absence of antibiotic selection is not trivial, and varies depending on the environment and genetic background of the strain. A good review can be found here. Beyond simple metabolic costs, there is some recent research that ...


4

Secondary ectothermy has been suggested in living crocodylians by Seymour et al. (2004). Their rationale is based on: Presence of a 4 chambered heart (otherwise only found in endotherms) Post-cardiac shunting via the foramen of Panizza and "cog-tooth" valve, which develop secondarily in crocodylians Lung structure and ventilation during locomotion Thus ...


3

In the paper you cite, we see KA and KS defined by the authors. The direct comparison between a pair of known nucleotide sequences in coding regions permits us to evaluate both the nucleotide differences per site caused by nucleotide substitutions leading to amino acid changes, KA, and those leading to synonymous changes, KS, simultaneously. The ...


3

I am curious, is there any known disease/infection that is very severe normally, but ends up having little to no effect on the lives of asymptomatic carriers? HIV is an obvious example, where so-called "long-term nonprogressors" successfully suppress HIV replication sufficiently that they do not develop AIDS but are unable to clear the infection entirely [1]...


2

Properly speaking, you should not use the word "design" when talking about evolution. All you can describe are more or less fit variations. A variation that is advantageous in one context can be detrimental in another. That being said, I assume what you are asking is whether the eyes could be better, as if an engineer would design them from scratch. The ...


2

"Natural selection" is a somewhat misleading term. Evolution does not need "natural" selection to occur; it only needs selection. Even the term "selection" is a bit misleading because it's often thought of as referring to the death of individuals or, somewhat more accurately, as reduced likelihood of producing offspring, due to lower fitness. In fact, any ...


2

There is no evolutionary "ratchet" that prevents a life form from evolving "backwards". However, it is statistically unlikely because it would pretty much require all of the environmental factors that changed during the transition from "cold blooded" to "warm-blooded" to change back in the reverse order, because all of those factors contributed to the ...


1

As mentioned, antibiotic resistance is actually quite expensive. Bacteria that fail to discard it when antibiotics are not present will be wiped out by competition from other bacteria that devote more resources to reproduction. One major source of antibiotic resistance is the 'multidrug efflux pump' which transports harmful chemicals outside the cell. You ...


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