In a study in which people played tug-of-war while blindfolded, it was found that a person pulled harder if the person thought he or she was competing alone, while pulling less hard when the person thought others were pulling as a team. This study illustrates:

Answerboth technicians (a) and (b);

How is it possible that phylogenies based on sequences from nuclear genomes and organellar genomes (i.e., chloroplasts and mitochondria) from the same group of species yield phylogenetic trees with different branching orders?   answer :   the genome of the endosymbiont is more closely related to members of the group in which it originally evolved, while the nuclear genome of the engulfing organism has its own evolutionary trajectory.

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