Final answer:
Group selection is not considered likely because selfish individuals within a group can gain a fitness advantage, undermining group benefit, while natural selection acts primarily at the individual level to enhance evolutionary fitness through reproduction.
Step-by-step explanation:
Group selection is not considered to be a likely evolutionary pressure because within a group of cooperators, selfish individuals may gain a fitness advantage over others. These individuals can spread their alleles through the population at the expense of the group's overall benefit. Although groups that perform well may grow and be more successful in some aspects, individual-level selection tends to be a stronger force. This is because natural selection acts at the level of the individual, selecting for those with greater contributions to the gene pool of the next generation. With the concept of evolutionary fitness, we understand that traits or behaviors that increase an individual's chance of survival and reproduction will become more common in a population over time, as those individuals pass their genes on to more offspring. This is part of the process of evolution by natural selection, which ultimately challenges the idea of group selection being a dominant evolutionary strategy.